Jack T. O'Malley-James, Jane S. Greaves, John A. Raven et al.

International Journal of Astrobiology • 2013

<jats:title>Abstract</jats:title><jats:p>The future biosphere on Earth (as with its past) will be made up predominantly of unicellular micro-organisms. Unicellular life was probably present for at least 2.5 Gyr before multicellular life appeared and will likely be the only form of life capable of surviving on the planet in the far future, when the ageing Sun causes environmental conditions to become more hostile to more complex forms of life. Therefore, it is statistically more likely that habitable Earth-like exoplanets we discover will be at a stage in their habitable lifetime more conducive to supporting unicellular, rather than multicellular life. The end stage of habitability on Earth is the focus of this work. A simple, latitude-based climate model incorporating eccentricity and obliquity variations is used as a guide to the temperature evolution of the Earth over the next 3 Gyr. This allows inferences to be made about potential refuges for life, particularly in mountains and cold-trap (ice) caves and what forms of life could live in these environments. Results suggest that in high latitude regions, unicellular life could persist for up to 2.8 Gyr from present. This begins to answer the question of how the habitability of Earth will evolve at local scales alongside the Sun's main sequence evolution and, by extension, how the habitability of Earth-like planets would evolve over time with their own host stars.</jats:p>

Frank T. Robb, Stephen M. Techtmann

F1000Research • 0

<ns4:p>Microbial adaptation to extreme conditions takes many forms, including specialized metabolism which may be crucial to survival in adverse conditions. Here, we analyze the diversity and environmental importance of systems allowing microbial carbon monoxide (CO) metabolism. CO is a toxic gas that can poison most organisms because of its tight binding to metalloproteins. Microbial CO uptake was first noted by Kluyver and Schnellen in 1947, and since then many microbes using CO via oxidation have emerged. Many strains use molecular oxygen as the electron acceptor for aerobic oxidation of CO using Mo-containing CO oxidoreductase enzymes named CO dehydrogenase. Anaerobic carboxydotrophs oxidize CO using CooS enzymes that contain Ni/Fe catalytic centers and are unrelated to CO dehydrogenase. Though rare on Earth in free form, CO is an important intermediate compound in anaerobic carbon cycling, as it can be coupled to acetogenesis, methanogenesis, hydrogenogenesis, and metal reduction. Many microbial species—both bacteria and archaea—have been shown to use CO to conserve energy or fix cell carbon or both. Microbial CO formation is also very common. Carboxydotrophs thus glean energy and fix carbon from a “metabolic leftover” that is not consumed by, and is toxic to, most microorganisms. Surprisingly, many species are able to thrive under culture headspaces sometimes exceeding 1 atmosphere of CO. It appears that carboxydotrophs are adapted to provide a metabolic “currency exchange” system in microbial communities in which CO arising either abiotically or biogenically is converted to CO<ns4:sub>2</ns4:sub>and H<ns4:sub>2</ns4:sub>that feed major metabolic pathways for energy conservation or carbon fixation. Solventogenic CO metabolism has been exploited to construct very large gas fermentation plants converting CO-rich industrial flue emissions into biofuels and chemical feedstocks, creating renewable energy while mitigating global warming. The use of thermostable CO dehydrogenase enzymes to construct sensitive CO gas sensors is also in progress.</ns4:p>

Jeffrey C. Way, Pamela A. Silver, Russell J. Howard

International Journal of Astrobiology • 2011

<jats:title>Abstract</jats:title><jats:p>Long space flights and planetary settlement will require sources of nutrition and chemicals that must be generated in space. This will include not only amino acids and vitamins but also oxygen, all of which can be generated by means of biosynthesis. Synthetic biology has the potential to generate organisms designed for supplying human nutritional needs in space. Photosynthetic microbes may be ideal for this purpose, as they are more efficient per volume cultivated than green plants at conversion of light to chemical energy, biomass and nutritional molecules. In addition, microbes are easier and faster to genetically engineer, facilitating not only design and terrestrial manufacture of organisms optimized for growth and nutrient production in the artificial conditions of space, but superior ability in space to develop organisms suited to newly discovered environments. The rapid ability to adapt and create new microbes to suit new circumstances when in space offers significant potential for risk reduction. Development of sun-driven microbial production of nutritional chemicals would also have terrestrial benefits in commerce and sustainability. A synthetic biology approach to chemical production would not be based on fossil fuels as such fuels do not exist on other planets. This approach would highlight a synergistic relationship between outer space and ‘spaceship earth’, illustrating NASA's role in stimulating technology development with terrestrial application. Two specific approaches deserve consideration: production by traditional photosynthetic microbes, or by the newly appreciated capacity of some bacteria to absorb electric current (e.g. solar panels) to drive metabolism. Palatability and sensory stimulation are a key part of food consumption and could be engineered into microbes. As a first step, NASA should test a bioreactor in which genetically engineered, nutrient-producing photosynthetic bacteria are grown and harvested in space.</jats:p>

Laura C. Kelly, Charles S. Cockell, Stephen Summers

International Journal of Astrobiology • 2012

<jats:title>Abstract</jats:title><jats:p>Planetary protection regulations are in place to control the contamination of planets and moons with terrestrial micro-organisms in order to avoid jeopardizing future scientific investigations relating to the search for life. One environmental chemical factor of relevance in extraterrestrial environments, specifically in the moons of the outer solar system, is ammonia (NH<jats:sub>3</jats:sub>). Ammonia is known to be highly toxic to micro-organisms and may disrupt proton motive force, interfere with cellular redox reactions or cause an increase of cell pH. To test the survival potential of terrestrial micro-organisms exposed to such cold, ammonia-rich environments, and to judge whether current planetary protection regulations are sufficient, soil samples were exposed to concentrations of NH<jats:sub>3</jats:sub>from 5 to 35% (v/v) at −80°C and room temperature for periods up to 11 months. Following exposure to 35% NH<jats:sub>3</jats:sub>, diverse spore-forming taxa survived, including representatives of the<jats:italic>Firmicutes</jats:italic>(<jats:italic>Bacillus, Sporosarcina, Viridibacillus, Paenibacillus, Staphylococcus</jats:italic>and<jats:italic>Brevibacillus</jats:italic>) and<jats:italic>Actinobacteria</jats:italic>(<jats:italic>Streptomyces</jats:italic>). Non-spore forming organisms also survived, including<jats:italic>Proteobacteria</jats:italic>(<jats:italic>Pseudomonas</jats:italic>) and<jats:italic>Actinobacteria</jats:italic>(<jats:italic>Arthrobacter</jats:italic>) that are known to have environmentally resistant resting states.<jats:italic>Clostridium</jats:italic>spp. were isolated from the exposed soil under anaerobic culture. High NH<jats:sub>3</jats:sub>was shown to cause a reduction in viability of spores over time, but spore morphology was not visibly altered. In addition to its implications for planetary protection, these data show that a large number of bacteria, potentially including spore-forming pathogens, but also environmentally resistant non-spore-formers, can survive high ammonia concentrations.</jats:p>

D. Mao, Lu Lu, A. Revil et al.

Environmental Science &amp; Technology • 2016

Efficient noninvasive techniques are desired for monitoring the remediation process of contaminated soils. We applied the direct current resistivity technique to image conductivity changes in sandbox experiments where two sandy and clayey soils were initially contaminated with diesel hydrocarbon. The experiments were conducted over a 230 day period. The removal of hydrocarbon was enhanced by a bioelectrochemical system (BES) and the electrical potentials of the BES reactors were also monitored during the course of the experiment. We found that the variation in electrical conductivity shown in the tomograms correlate well with diesel removal from the sandy soil, but this is not the case with the clayey soil. The clayey soil is characterized by a larger specific surface area and therefore a larger surface conductivity. In sandy soil, the removal of the diesel and products from degradation leads to an increase in electrical conductivity during the first 69 days. This is expected since diesel is electrically insulating. For both soils, the activity of BES reactors is moderately imaged by the inverted conductivity tomogram of the reactor. An increase in current production by electrochemically active bacteria activity corresponds to an increase in conductivity of the reactor.

Dandan Liu, Tianye Zheng, C. Buisman et al.

ACS Sustainable Chemistry &amp; Engineering • 2017

Methane-producing bioelectrochemical systems (BESs) are a promising technology to convert renewable surplus electricity into the form of storable methane. One of the key challenges for this technology is the search for suitable cathode materials with improved biocompatibility and low cost. Here, we study heat-treated stainless steel felt (HSSF) for its performance as biocathode. The HSSF had superior electrocatalytic properties for hydrogen evolution compared to untreated stainless steel felt (SSF) and graphite felt (GF), leading to a faster start-up of the biocathodes. At cathode potentials of −1.3 and −1.1 V, the methane production rates for HSSF biocathodes were higher than the SSF, while its performance was similar to GF biocathodes at −1.1 V and lower than GF at −1.3 V. The HSSF biocathodes had a current-to-methane efficiency of 60.8% and energy efficiency of 21.9% at −1.3 V. HSSF is an alternative cathode material with similar performance compared to graphite felt, suited for application in methane-producing BESs.

Yuan Pan, T. Zhu, Zhen He

Industrial &amp; Engineering Chemistry Research • 2018

Azo dyes and their decolorized products are toxic and persistent to biodegradation, but must be properly removed before dye wastewater being discharged to a water body. In this study, a bioelectrochemical system (BES) combined with a membrane biofilm reactor (MBfR) has been investigated for removing azo dye and its reduction products. Acid orange 7 (AO7) as a model azo dye was efficiently removed (96.5 ± 0.6%) in the BES cathode, and its reduction product - sulfanilic acid was further degraded by the MBfR (64.7 ± 2.7%) at a lumen pressure of 30 psi. Loop operation eliminated the anode substrate addition by taking advantages of residue substrate from the MBfR. The energy consumption by this integrated system was estimated between 1.31 ± 0.01 and 2.33 ± 0.05 kWh kg AO7–1. It was demonstrated by cyclic voltammetry that decolorization products of the AO7 contained in the MBfR effluent could serve as redox mediators for enhancing current generation in the BES.

D. A. Moreno-Jimenez, Kyoung-Yeol Kim

SSRN Electronic Journal • 2022

A nickel-functionalized activated carbon (AC/Ni) was recently developed for microbial electrolysis cells (MECs) and showed a great potential for large-scale applications. In this study, the electroactivity of the AC/Ni cathode was significantly improved by increasing the oxygen (16.9%) and nitrogen (124%) containing species on the AC using nitric acid oxidation. The acid-treated AC (t-AC) showed 21% enhanced wettability that consequently reduced the ohmic resistance (6.7%) and the charge transfer resistance (33.3%). As a result, t-AC/Ni achieved peak values of hydrogen production rate (0.35±0.02 L-H2/L-d), energy yield (129±8%), and cathodic hydrogen recovery (93±6%) in MECs. The hydrogen production rate was 84% higher using t-AC/Ni cathode than the control, likely due to the enhanced wettability and a higher fraction of N on the t-AC. Also, the increases in polyvinylidene fluoride (PVDF) binder loadings (from 4.6 mg-PVDF/cm2 to 7.3 mg-PVDF/cm2) demonstrated 47% higher hydrogen productions rates in MECs.

Irina Amar Dubrovin, Lea Ouaknin Hirsch, Shmuel Rozenfeld et al.

Microorganisms • 2022

Microbial electrolysis cells (MECs) are an emerging technology capable of harvesting part of the potential chemical energy in organic compounds while producing hydrogen. One of the main obstacles in MECs is the bacterial anode, which usually contains mixed cultures. Non-exoelectrogens can act as a physical barrier by settling on the anode surface and displacing the exoelectrogenic microorganisms. Those non-exoelectrogens can also compete with the exoelectrogenic microorganisms for nutrients and reduce hydrogen production. In addition, the bacterial anode needs to withstand the shear and friction forces existing in domestic wastewater plants. In this study, a bacterial anode was encapsulated by a microfiltration membrane. The novel encapsulation technology is based on a small bioreactor platform (SBP) recently developed for achieving successful bioaugmentation in wastewater treatment plants. The 3D capsule (2.5 cm in length, 0.8 cm in diameter) physically separates the exoelectrogenic biofilm on the carbon cloth anode material from the natural microorganisms in the wastewater, while enabling the diffusion of nutrients through the capsule membrane. MECs based on the SBP anode (MEC-SBPs) and the MECs based on a nonencapsulated anode (MEC control) were fed with Geobacter medium supplied with acetate for 32 days, and then with artificial wastewater for another 46 days. The electrochemical activity, chemical oxygen demand (COD), bacterial anode viability and relative distribution on the MEC-SBP anode were compared with the MEC control. When the MECs were fed with artificial wastewater, the MEC-SBP produced (at −0.6 V) 1.70 ± 0.22 A m−2, twice that of the MEC control. The hydrogen evolution rates were 0.017 and 0.005 m3 m−3 day−1, respectively. The COD consumption rate for both was about the same at 650 ± 70 mg L−1. We assume that developing the encapsulated bacterial anode using the SBP technology will help overcome the problem of contamination by non-exoelectrogenic bacteria, as well as the shear and friction forces in wastewater plants.

N. Madondo, E. Kweinor Tetteh, S. Rathilal et al.

Molecules • 2022

This study examined the application of an electromagnetic field to anaerobic digestion by using an electromagnetic system (ES), a microbial electrolysis cell (MEC), and a control with no external force. The experimental work was performed by carrying out biochemical methane potential (BMP) tests using 1 L biodigesters. The bioelectrochemical digesters were supplied with 0.4 V for 30 days at 40 °C. The electromagnetic field of the ES was generated by coiling copper wire to form a solenoid in the BMP system, whereas the MEC consisted of zinc and copper electrodes inside the BMP system. The best performing system was the MEC, with a yield of 292.6 mL CH4/g chemical oxygen demand removed (CODremoved), methane content of 86%, a maximum current density of 23.3 mA/m2, a coulombic efficiency of 110.4%, and an electrical conductivity of 180 µS/cm. Above 75% removal of total suspended solids (TSS), total organic carbon (TOC), phosphate, and ammonia nitrogen (NH3-N) was also recorded. However, a longer exposure (>8 days) to higher magnetic intensity (6.24 mT) on the ES reduced its overall performance. In terms of energy, the MEC produced the greatest annual energy profit (327.0 ZAR/kWh or 23.36 USD/kWh). The application of an electromagnetic field in anaerobic digestion, especially a MEC, has the potential to maximize the methane production and the degradability of the wastewater organic content.

M. Rebezov, K. Saeed, A. Khaliq et al.

Applied Sciences • 2022

Electrolyzed water is a novel disinfectant and cleaner that has been widely utilized in the food sector for several years to ensure that surfaces are sterilized, and that food is safe. It is produced by the electrolysis of a dilute salt solution, and the reaction products include sodium hydroxide (NaOH) and hypochlorous acid. In comparison to conventional cleaning agents, electrolyzed water is economical and eco-friendly, easy to use, and strongly effective. Electrolyzed water is also used in its acidic form, but it is non-corrosive to the human epithelium and other organic matter. The electrolyzed water can be utilized in a diverse range of foods; thus, it is an appropriate choice for synergistic microbial control in the food industry to ensure food safety and quality without damaging the organoleptic parameters of the food. The present review article highlights the latest information on the factors responsible for food spoilage and the antimicrobial potential of electrolyzed water in fresh or processed plant and animal products.

Joseph Hartvigsen, S Elangovan, Jessica Elwell et al.

ECS Meeting Abstracts • 2017

<jats:p> Space exploration poses some of the highest risk humans encounter in the course of scientific investigation. It requires a logistics supply not only of food, fuel and tools, but also sophisticated environmental control with atmosphere revitalization and oxidizer for propulsion during the return to Earth. The cost of lifting initial mass into low earth orbit (IM-LEO) is significant. For a mission to Mars, the additional delivery costs associated with transit, entry, decent and landing (EDL) on Mars will multiply the mass specific value of supplies needed on the surface of Mars. For decades, the concept of exploiting local resources, (in situ resource utilization or ISRU) has been accepted as a foundational mission design basis in manned space mission planning, but no such system has been flown to date. In 2014, NASA announced an experiment suite for the Mars 2020 mission, a Curiosity-class Mars rover, that would include MOXIE, the Mars Oxygen ISRU Experiment. This first non-terrestrial ISRU experiment will demonstrate the initial feasibility of solid oxide electrolysis of Martian atmosphere CO<jats:sub>2</jats:sub> as a means of producing oxygen for propellant oxidant in a Mars Ascent Vehicle (MAV). </jats:p> <jats:p>Ceramatec is developing the solid oxide electrolysis cell (SOEC, aka SOXE) stack for MOXIE. The rover host platform for the MOXIE project imposes severe constraints on mass, volume, peak power and total cycle energy, but it offers an early opportunity to demonstrate non-terrestrial ISRU with only the incremental cost of developing and delivering the 15kg MOXIE system on a 1050kg rover. Additional challenges arise in an unmanned operational environment, with once daily uplink and downlink schedules making man in the loop operation infeasible. Therefore, care must be taken to define a safe operating envelope in such a way that the system can be reliably operated without damaging itself as there is no option for a service call as was done for Hubble. </jats:p> <jats:p>Mars atmosphere, which is about 96% CO<jats:sub>2</jats:sub>, is supplied to the solid oxide electrolysis stack by means of a scroll compressor. The scroll pump is a fixed displacement device, so the delivered flow rate of CO<jats:sub>2</jats:sub> will depend on pump rpm and the atmospheric density, which varies as a function of landing site elevation as well as seasonal and diurnal atmosphere cycles. The landing site has not yet been selected, but even after determining the landing site, the atmospheric density still varies over a wide range. Therefore, MOXIE must be able to operate over a wide range of feeds rates. </jats:p> <jats:p>Other than electric power, limited thermal stability and telemetry, the rover provides no process utilities such as air, hydrogen, nitrogen, or water to MOXIE. MOXIE can only take in filtered Mars atmosphere, and in an unattended operation, produce oxygen from the CO<jats:sub>2</jats:sub> in the atmosphere. </jats:p> <jats:p>A nickel cermet cathode is oxidized by pure CO<jats:sub>2</jats:sub> at 800°C which results in a loss of conductivity and a disruption of the microstructure due to volume expansion on oxidation. A combination of high cell operating voltage and CO<jats:sub>2</jats:sub> utilization will lead to carbon deposition which can irreversibly destroy the cathode and plug the cathode flow channels. These thermodynamic and resulting electrochemical boundaries have been mapped analytically and have been used to develop system configurations and operating strategies to protect against cathode oxidation and CO reduction to solid carbon. These approaches have been and continue to be validated experimentally with increasing degrees of system integration. The MOXIE stack process integration and operational development path and results will be presented. </jats:p> <jats:p>Acknowledgment: This material is based upon work supported by NASA through JPL’s prime contract under JPL subcontract number 1515459. </jats:p>

F. Figueredo, E. Cortón, X. Abrevaya

Astrobiology • 2015

Microbial fuel cells (MFCs) are bioelectrochemical systems (BES) capable of harvesting electrons from redox reactions involved in metabolism. In a previous work, we used chemoorganoheterotrophic microorganisms from the three domains of life-Bacteria, Archaea, and Eukarya-to demonstrate that these BES could be applied to the in situ detection of extraterrestrial life. Since metabolism can be considered a common signature of life "as we know it," we extended in this study the ability to use MFCs as sensors for photolithoautotrophic metabolisms. To achieve this goal, two different photosynthetic microorganisms were used: the microalgae Parachlorella kessleri and the cyanobacterium Nostoc sp. MFCs were loaded with nonsterilized samples, sterilized samples, or sterilized culture medium of both microorganisms. Electric potential measurements were recorded for each group in single experiments or in continuum during light-dark cycles, and power and current densities were calculated. Our results indicate that the highest power and current density values were achieved when metabolically active microorganisms were present in the anode of the MFC. Moreover, when continuous measurements were performed during light-dark cycles, it was possible to see a positive response to light. Therefore, these BES could be used not only to detect chemoorganoheterotrophic metabolisms but also photolithoautotrophic metabolisms, in particular those involving oxygenic photosynthesis. Additionally, the positive response to light when using these BES could be employed to distinguish photosynthetic from nonphotosynthetic microorganisms in a sample.

Leila Chebbo, Hasnain Nisar, Ali Bazzi

AIAA Journal • 2025

<jats:p> This research investigates the possible failures caused by aging and other environmental and external factors that could significantly impact the performance of extraterrestrial power systems. Additionally, it presents a reliability assessment model for the space microgrid based on fault tree analysis (FTA). The reliability assessment model developed in this paper represents a tool that can be used by engineers to harden the system design for operational and economic benefits. To improve the reliability of the system, this work provides a broad review of the different fault detection and diagnosis (FDD) algorithms used for power microgrids and space applications. Using data sets from the Habitat Simulator developed through the NASA-funded Resilient Extraterrestrial Habitat Institute, this paper compares the applicability and accuracy of the different FDD methods. The primary FDD approach proposed and assessed in this work is based on the Markov reliability model. It predicts and detects future faults in the space microgrids by using past data samples and categorizing them into different classes. Data-driven-based models such as artificial neural networks are also investigated, tested, and evaluated using simulation data sets. According to the simulation results and the broad FDD algorithm comparison, this study provides the crew or maintenance engineers with a clear methodology to detect and localize power system failures. </jats:p>

Bin Lai, Shiqin Yu, P. Bernhardt et al.

Biotechnology for Biofuels • 2016

BackgroundPseudomonas putida is a promising host for the bioproduction of chemicals, but its industrial applications are significantly limited by its obligate aerobic character. The aim of this paper is to empower the anoxic metabolism of wild-type Pseudomonas putida to enable bioproduction anaerobically, with the redox power from a bioelectrochemical system (BES).ResultsThe obligate aerobe Pseudomonas putida F1 was able to survive and produce almost exclusively 2–Keto-gluconate from glucose under anoxic conditions due to redox balancing with electron mediators in a BES. 2-Keto-gluconate, a precursor for industrial anti-oxidant production, was produced at an overall carbon yield of over 90 % based on glucose. Seven different mediator compounds were tested, and only those with redox potential above 0.207 V (vs standard hydrogen electrode) showed interaction with the cells. The productivity increased with the increasing redox potential of the mediator, indicating this was a key factor affecting the anoxic production process. P. putida cells survived under anaerobic conditions, and limited biofilm formation could be observed on the anode’s surface. Analysis of the intracellular pools of ATP, ADP and AMP showed that cells had an increased adenylate energy charge suggesting that cells were able to generate energy using the anode as terminal electron acceptor. The analysis of NAD(H) and NADP(H) showed that in the presence of specific extracellular electron acceptors, the NADP(H) pool was more oxidised, while the NAD(H) pool was unchanged. This implies a growth limitation under anaerobic conditions due to a shortage of NADPH and provides a way to limit biomass formation, while allowing cell maintenance and catalysis at high purity and yield.ConclusionsFor the first time, this study proved the principle that a BES-driven bioconversion of glucose can be achieved for a wild-type obligate aerobe. This non-growth bioconversion was in high yields, high purity and also could deliver the necessary metabolic energy for cell maintenance. By combining this approach with metabolic engineering strategies, this could prove to be a powerful new way to produce bio-chemicals and fuels from renewables in both high yield and high purity.

N. Triroj, R. Saensak, S. Porntheeraphat et al.

Analytical Chemistry • 2020

This work aims to utilize diamond-like carbon (DLC) thin films for bioreceptor immobilization and amperometric biosensing in a microfluidic platform. A specific RF-PECVD method was employed to prepare DLC thin film electrodes with desirable surface and bulk properties. The films possessed a relatively high sp2 fraction, a moderate electrical conductivity (7.75 × 10-3 S·cm-1), and an optical band gap of 1.67 eV. X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed a presence of oxygen-containing functional groups on the DLC surface. The DLC electrodes were integrated into polydimethylsiloxane (PDMS) microfluidic electrochemical cells with the channel volume of 2.24 µL. Glucose oxidase (GOx) was chosen as a model bioreceptor to validate the employment of DLC electrodes for bioelectrochemical sensing. In-channel immobilization of glucose oxidase (GOx) at the DLC surface was realized through carbodiimide covalent linkages. Enzyme bound DLC electrode was confirmed with the redox potential at around -79 mV vs. NHE in 0.1 M phosphate buffer pH 7.4. Amperometric flow-injection glucose sensing at a potential of -0.45 V vs. Ag in the absence of standard redox mediators showed the increase of current response upon increasing of glucose concentration. The sensing mechanism is based on the reduction process of H2O2 liberated from the enzymatic activity. The proposed model for the catalytic H2O2 reduction to H2O on DLC electrodes was attributed to the dissociation of C-O bonds at the DLC surface.

Guoda Vecelytė, Vygailė Dudkaitė, O. Šedo et al.

Materials Horizons • 2025

The potential of bioconjugated glucose oxidase enzymes for bioelectronic applications has been revealed in this research. By selectively modifying the enzyme with redox-active groups, we aimed to enhance the electrochemical properties of the enzyme while maintaining its biocatalytic activity. The phenothiazin-5-oxide and phenoxazine groups were selectively bioconjugated to the tyrosine residues on the enzyme surface. This bioconjugation was confirmed by mass spectrometry after enzymatic digestion of the protein. The self-assembly monolayer of modified enzyme exhibited improved bioelectrochemical behaviour, with enhanced anodic currents compared to the native enzyme. Marcus theory-based theoretical calculations revealed that hole hopping through the internal residues and from the electrode to the bioconjugated residues of the enzyme is thermodynamically favourable. The rate-limiting step for the bioelectrocatalytic process was identified as hole injection from the electrode to the bioconjugated enzyme surface. These findings demonstrate the potential of bioconjugated glucose oxidase for single molecule-based biosensing and bioelectronics.

Dong Sup Kim, Xiaoguang Yang, Ja Hyun Lee et al.

Biosensors • 2022

Electrochemical nano-biosensor systems are popular in the industrial field, along with evaluations of medical, agricultural, environmental and sports analysis, because they can simultaneously perform qualitative and quantitative analyses with high sensitivity. However, real-time detection using an electrochemical nano-biosensor is greatly affected by the surrounding environment with the performance of the electron transport materials. Therefore, many researchers are trying to find good factors for real-time detection. In this work, it was found that a composite composed of graphite oxide/cobalt/chitosan had strong stability and electron transfer capability and was applied to a bioelectrochemical nano-biosensor with high sensitivity and stability. As a mediator-modified electrode, the GO/Co/chitosan composite was electrically deposited onto an Au film electrode by covalent boding, while glucose oxidase as a receptor was immobilized on the end of the GO/Co/chitosan composite. It was confirmed that the electron transfer ability of the GO/Co/chitosan composite was excellent, as shown with power density analysis. In addition, the real-time detection of D-glucose could be successfully performed by the developed nano-biosensor with a high range of detected concentrations from 1.0 to 15.0 mM. Furthermore, the slope value composed of the current, per the concentration of D-glucose as a detection response, was significantly maintained even after 14 days.

P. Cristiani, Laura Malavola, S. Franz et al.

E3S Web of Conferences • 2022

Thermotoga neapolitana is a hyperthermophilic bacterium that can metabolize glucose and several organic wastes in hydrogen and lactate at a temperature of 80°C. Their high performance in producing hydrogen at so high a temperature as 80°C suggests a potential energy application of them where hydrogen is an important element of the process. In this view, experimentation of a T.neapolitana strain is carried out in double-chamber electrochemical systems. The aim is to explore the interaction of these bacteria with the anode and the cathode, stressing their capability to survive in presence of a polarized electrode which can drastically change the pH of the media. A culture enriched of 5 g/L of glucose, under CO2 pressure (80 °C) was used to fill both the anodic and cathodic compartments of the electrochemical system, applying a voltage of 1.5 V between the anode and the cathode. The test lasted ten days. Results clearly indicate that bacteria colonize both electrodes, but the glucose metabolism is completely inhibited in the anodic compartments. On the contrary, metabolism is stimulated in the cathodic compartment. Bacteria are alive on the electrodes in the pH interval of 3 - 9.

Elžbieta Ragauskaitė, Samuelis Marčiukaitis, Ingrida Radveikienė et al.

Nanoscale • 2024

Polyaniline (PANI), a nanostructured conducting polymer, has shown significant potential in optical and bioelectrochemical devices. However, its performance and stability on various substrates are hindered by weak adhesion to the surface. In this study, a strongly adherent polyaniline conducting polymer layer with a thickness of five nanometers was electrografted onto an initiating monolayer on gold and tin-doped indium oxide substrates. These electrografted monolayers consist of vertically oriented fully oxidized-protonated (pernigraniline salt) and deprotonated (pernigraniline base) forms of polyaniline. The monolayer exhibits pH-dependent colour changes and it is suitable for enzyme compatibility. In light of these findings, we have developed and characterized an electrochemical glucose biosensor based on the monolayer of polyaniline on a gold electrode. The biosensor utilizes glucose oxidase as the biorecognition element for the selective detection of glucose concentrations in real blood plasma samples.

Xinyu Wang, D. Xing, Xiaoxue Mei et al.

Frontiers in Microbiology • 2018

p-Nitrophenol (PNP) is common in the wastewater from many chemical industries. In this study, we investigated the effect of initial concentrations of PNP and glucose and applied voltage on PNP reduction in biocathode BESs and open-circuit biocathode BESs (OC-BES). The PNP degradation efficiency of a biocathode BES with 0.5 V (Bioc-0.5) reached 99.5 ± 0.8%, which was higher than the degradation efficiency of the BES with 0 V (Bioc-0) (62.4 ± 4.5%) and the OC-BES (59.2 ± 12.5%). The PNP degradation rate constant (kPNP) of Bioc-0.5 was 0.13 ± 0.01 h-1, which was higher than the kPNP of Bioc-0 (0.024 ± 0.002 h-1) and OC-BES (0.013 ± 0.0005 h-1). PNP degradation depended on the initial concentrations of glucose and PNP. A glucose concentration of 0.5 g L-1 was best for PNP degradation. The initial PNP increased from 50 to 130 mg L-1 and the kPNP decreased from 0.093 ± 0.008 to 0.027 ± 0.001 h-1. High-throughput sequencing of 16S rRNA gene amplicons indicated differences in microbial community structure between BESs with different voltages and the OC-BES. The predominant populations were affiliated with Streptococcus (42.7%) and Citrobacter (54.1%) in biocathode biofilms of BESs, and Dysgonomonas were the predominant microorganisms in biocathode biofilms of OC-BESs. The predominant populations were different among the cathode biofilms and the suspensions. These results demonstrated that applied voltage and biocathode biofilms play important roles in PNP degradation.

Laura Pause, Anna Weimer, Nicolas T. Wirth et al.

Microbial Biotechnology • 2024

<jats:title>Abstract</jats:title><jats:p>Providing an anodic potential in a bio‐electrochemical system to the obligate aerobe <jats:italic>Pseudomonas putida</jats:italic> enables anaerobic survival and allows the cells to overcome redox imbalances. In this setup, the bacteria could be exploited to produce chemicals via oxidative pathways at high yield. However, the absence of anaerobic growth and low carbon turnover rates remain as obstacles for the application of such an electro‐fermentation technology. Growth and carbon turnover start with carbon uptake into the periplasm and cytosol. <jats:italic>P. putida</jats:italic> KT2440 has three native transporting systems for glucose, each differing in energy and redox demand. This architecture previously led to the hypothesis that internal redox and energy constraints ultimately limit cytoplasmic carbon utilization in a bio‐electrochemical system. However, it remains largely unclear which uptake route is predominantly used by <jats:italic>P. putida</jats:italic> under electro‐fermentative conditions. To elucidate this, we created three gene deletion mutants of <jats:italic>P. putida</jats:italic> KT2440, forcing the cells to exclusively utilize one of the routes. When grown in a bio‐electrochemical system, the pathway mutants were heavily affected in terms of sugar consumption, current output and product formation. Surprisingly, however, we found that about half of the acetate formed in the cytoplasm originated from carbon that was put into the system via the inoculation biomass, while the other half came from the consumption of substrate. The deletion of individual sugar uptake routes did not alter significantly the secreted acetate concentrations among different strains even with different carbon sources. This means that the stoichiometry of the sugar uptake routes is not a limiting factor during electro‐fermentation and that the low rates might be caused by other reasons, for example energy limitations or a yet‐to‐be‐identified oxygen‐dependent regulatory mechanism.</jats:p>

Shiqin Yu, Bin Lai, Manuel R. Plan et al.

Biotechnology and Bioengineering • 2018

<jats:title>Abstract</jats:title><jats:sec><jats:label/><jats:p>It was recently demonstrated that a bioelectrochemical system (BES) with a redox mediator allowed <jats:italic>Pseudomonas putida</jats:italic> to perform anoxic metabolism, converting sugar to sugar acids with high yield. However, the low productivity currently limits the application of this technology. To improve productivity, the strain was optimized through improved expression of glucose dehydrogenase (GCD) and gluconate dehydrogenase (GAD). In addition, quantitative real‐time RT‐PCR analysis revealed the intrinsic self‐regulation of GCD and GAD. Utilizing this self‐regulation system, the single overexpression strain (GCD) gave an outstanding performance in the electron transfer rate and 2‐ketogluconic acid (2KGA) productivity. The peak anodic current density, specific glucose uptake rate and 2KGA producing rate were 0.12 mA/cm<jats:sup>2</jats:sup>, 0.27 ± 0.02 mmol/g<jats:sub>CDW</jats:sub>/hr and 0.25 ± 0.02 mmol/g<jats:sub>CDW</jats:sub>/hr, which were 327%, 477%, and 644% of the values of wild‐type <jats:italic>P. putida</jats:italic> KT2440, respectively. This work demonstrates that expression of periplasmic dehydrogenases involved in electron transfer can significantly improve productivity in the BES.</jats:p></jats:sec>

D. Nosek, Tomasz Mikołajczyk, A. Cydzik‐Kwiatkowska

International Journal of Environmental Research and Public Health • 2023

This study investigated how anode electrode modification with iron affects the microbiome and electricity generation of microbial fuel cells (MFCs) fed with municipal wastewater. Doses of 0.0 (control), 0.05, 0.1, 0.2, and 0.4 g Fe2O3 per the total anode electrode area were tested. Fe2O3 doses from 0.05 to 0.2 g improved electricity generation; with a dose of 0.10 g Fe2O3, the cell power was highest (1.39 mW/m2), and the internal resistance was lowest (184.9 Ω). Although acetate was the main source of organics in the municipal wastewater, propionic and valeric acids predominated in the outflows from all MFCs. In addition, Fe-modification stimulated the growth of the extracellular polymer producers Zoogloea sp. and Acidovorax sp., which favored biofilm formation. Electrogenic Geobacter sp. had the highest percent abundance in the anode of the control MFC, which generated the least electricity. However, with 0.05 and 0.10 g Fe2O3 doses, Pseudomonas sp., Oscillochloris sp., and Rhizobium sp. predominated in the anode microbiomes, and with 0.2 and 0.4 g doses, the electrogens Dechloromonas sp. and Desulfobacter sp. predominated. This is the first study to holistically examine how different amounts of Fe on the anode affect electricity generation, the microbiome, and metabolic products in the outflow of MFCs fed with synthetic municipal wastewater.

Kamran Ayaz, Ewa Zabłocka-Godlewska, Chao Li

Energies • 2024

This study explores the efficient decolorization and complete mineralization of the diazo dye Evans blue, using an integrated aerobic bioreactor system coupled with a double-chamber microbial fuel cell (DCMFC) including a bio-cathode and acetate as a cosubstrate. The research addresses the environmental challenges posed by dye-laden industrial effluents, focusing on achieving high decolorization efficiency and understanding the microbial communities involved. The study utilized mixed strains of actinomycetes, isolated from garden compost, to treat initial dye concentrations of 100 mg/L and 200 mg/L. Decolorization efficiency and microbial community composition were evaluated using 16S rRNA sequencing, and electrochemical impedance spectroscopy (EIS) was used to assess anode and DCMFC resistance. The results demonstrated decolorization efficiencies ranging from 90 ± 2% to 98 ± 1.9% for 100 mg/L and from 79 ± 2% to 87% ± 1% for 200 mg/L. An anode resistance of 12.48 Ω indicated a well-developed biofilm and enhanced electron transfer. The microbial community analysis revealed a significant presence of Pseudomonadota (45.5% in dye-acclimated cultures and 32% in inoculum cultures), with key genera including Actinomarinicola (13.75%), Thermochromatium (4.82%), and Geobacter (4.52%). This study highlights the potential of the integrated DCMFC–aerobic system, utilizing mixed actinomycetes strains, for the effective treatment of industrial dye effluents, offering both environmental and bioenergy benefits.

Bibhabasu Mohanty, Meet Dhamsaniya

SPU Journal of Science, Technology and Management Research • 2024

Currently, microbial fuel cells (MFC) provide viable options for both generating power and treating wastewater. A microbial fuel cell (MFC) is a cutting-edge technology that offers an efficient solution to the problems presented by costly and ecologically damaging energy generation systems reliant on fossil fuels. This study involved the creation of a dual-phase microbial fuel cell (MFC) and the subsequent conduction of experiments in two distinct stages. The initial stage of the experiment was the use of home sewage and dairy effluent, without the addition of any substrate. The second part of the experiment involved the use of residential sewage and dairy effluent, with sodium acetate serving as the substrate. An analysis was conducted on the physiochemical parameters of wastewater in both stages, including color, odour, pH, COD, BOD, TDS, and TSS. The experimental run yielded removal efficiencies of 83.4% for COD and 64.8% for BOD in dairy effluent, 78.4% for COD and 60.4% for BOD in domestic sewage with substrate addition, 75.5% for COD and 53.6% for BOD in dairy effluent, and 63.1% for COD and 58.1% for BOD in domestic wastewater without substrate addition. The voltage produced in the initial phase, in the absence of substrate, during the treatment of household and dairy wastewater was 702.2 mV and 738.5 mV, respectively. During the second phase, the voltage created for treating household wastewater was 725.4 mV, whereas for dairy wastewater it was 753.2 mV. The voltage produced during the treatment of dairy effluent is higher in both stages of the experimental trial. The study showed that organic matter in dairy wastewater degraded more efficiently and produced a higher quantity of electrons compared to household wastewater organic matter.

J. R. González-Paz, A. Ordaz, J. Jan-Roblero et al.

Revista Mexicana de Ingeniería Química • 2020

The aim of the present work was to btain a sulfidogenic sludge capable of th iving with acetate and evaluate its potential application as a source of microorganisms in a microbial fuel cell (MFC). The results showed that sulfate (SO−2 4 ) to sulfide (HS−) conversion increased from 74 ± 0.39% with a fed consisting of a mixture acetate:butyrate, to 85 ± 0.34% with a fed containing only acetate. The sulfate removal rate (SRR) was of 1755.30 ± 50 mg SO−2 4 gVSS −1 L−1 d−1 and sulfate reducing activity (SRA) 155.21 ± 30 mg COD-H2S gVSS−1 d−1 with the mixture and SRR 1692.31 ± 39 mg SO−2 4 gVSS −1 L−1 d−1 ; SRA 184.25 ± 24 mg COD-H2S gVSS−1 d−1 with acetate. The COD removal increased from 66 ± 0.8% with the mixture to 81 ± 0.39%, with acetate. The open circuit voltage increased from 0.668 to 0.788 V with acetate. The results suggested that this sludge could be utilized to recover energy that could be eventually susceptible to storage for further utilization while reducing sulfate and avoiding accumulation of acetate.

Yoshino Inohana, Shohei Katsuya, R. Koga et al.

Microbes and Environments • 2020

To identify exoelectrogens involved in the generation of electricity from complex organic matter in coastal sediment (CS) microbial fuel cells (MFCs), MFCs were inoculated with CS obtained from tidal flats and estuaries in the Tokyo bay and supplemented with starch, peptone, and fish extract as substrates. Power output was dependent on the CS used as inocula and ranged between 100 and 600 mW m–2 (based on the projected area of the anode). Analyses of anode microbiomes using 16S rRNA gene amplicons revealed that the read abundance of some bacteria, including those related to Shewanella algae, positively correlated with power outputs from MFCs. Some fermentative bacteria were also detected as major populations in anode microbiomes. A bacterial strain related to S. algae was isolated from MFC using an electrode plate-culture device, and pure-culture experiments demonstrated that this strain exhibited the ability to generate electricity from organic acids, including acetate. These results suggest that acetate-oxidizing S. algae relatives generate electricity from fermentation products in CS-MFCs that decompose complex organic matter.

Kha Lil Dinh, Chin‐Tsan Wang, H. Dai et al.

International Journal of Energy Research • 2021

For about 20 years, microbial fuel cells (MFCs) are an emerging technology that has gained attention for its new wastewater treatment and energy generation, especially its ability to convert chemical energy from a broad range of substances into electricity. However, MFC has not been widely commercialized due to low efficiency. Studies have shown that substrate loading is an important factor in scaling up. Therefore, this study investigates the effect of substrate type and concentration on honeycomb MFCs (HCMFCs). The effect of different concentrations ranging from 10 to 40 mM of lactate and acetate (1:1 ratio) substrates was investigated. Power efficiency was analyzed using polarization and power density curves. Results showed that the performance of MFCs and biofilm formation is affected by the substrates. Scanning electron microscopy showed some changes in biofilm formation. Mixing lactate and acetate at 30 mM gave the best performance with a power density of 956.75 mW m−2 and chemical oxygen demand removal of 87.8%. Furthermore, effective substrate degradation, having COD removal of 91.4%, was observed with acetate.

Burak Kilinç, T. Catal

Polish Journal of Environmental Studies • 2023

In this study, a new soil-based microbial fuel cell was developed that can be used for biological remediation in areas with soil pollution. Electricity generation was studied with the developed soil-based microbial fuel cell. Voltage values were measured depending on time and the effects of sodium acetate at different concentrations (20, 40, 60, 80, 100 mM) were investigated. Our results showed that up to 396 mV electricity generation is possible with the new soil-based microbial fuel cell. The voltage values gradually increased with increasing sodium acetate concentration. The half-saturation constant was found to be 75.99 (R 2 = 0.97). In conclusion, the developed soil-based microbial fuel cell has shown that it has biosensor potential and can be used in the detection of various environmental pollutants.

Ludovic Jourdin, Yang Lu, Victoria Flexer et al.

ChemElectroChem • 2016

<jats:title>Abstract</jats:title><jats:p>Electron‐transfer pathways occurring in biocathodes are still unknown. We demonstrate here that high rates of acetate production by microbial electrosynthesis are mainly driven by an electron flux from the electrode to carbon dioxide, occurring via biologically induced hydrogen, with (99±1) % electron recovery into acetate. Nevertheless, acetate production is shown to occur exclusively within the biofilm. The acetate producers, putatively <jats:italic>Acetoanaerobium</jats:italic>, showed the remarkable ability to consume a high H<jats:sub>2</jats:sub> flux before it could escape from the biofilm. At zero wastage of H<jats:sub>2</jats:sub> gas, it allows superior production rates and lesser technical bottlenecks over technologies that rely on mass transfer of H<jats:sub>2</jats:sub> to microorganisms suspended in aqueous solution. This study suggests that bacterial modification of the electrode surface (possibly via synthesis of Cu nanoparticles) is directly involved in the significant enhancement of the hydrogen production.</jats:p>

Gowthami Palanisamy, Yeong Min Im, Ajmal P. Muhammed et al.

Membranes • 0

<jats:p>Developing a hybrid composite polymer membrane with desired functional and intrinsic properties has gained significant consideration in the fabrication of proton exchange membranes for microbial fuel cell applications. Among the different polymers, a naturally derived cellulose biopolymer has excellent benefits over synthetic polymers derived from petrochemical byproducts. However, the inferior physicochemical, thermal, and mechanical properties of biopolymers limit their benefits. In this study, we developed a new hybrid polymer composite of a semi-synthetic cellulose acetate (CA) polymer derivate incorporated with inorganic silica (SiO2) nanoparticles, with or without a sulfonation (–SO3H) functional group (sSiO2). The excellent composite membrane formation was further improved by adding a plasticizer (glycerol (G)) and optimized by varying the SiO2 concentration in the polymer membrane matrix. The composite membrane’s effectively improved physicochemical properties (water uptake, swelling ratio, proton conductivity, and ion exchange capacity) were identified because of the intramolecular bonding between the cellulose acetate, SiO2, and plasticizer. The proton (H+) transfer properties were exhibited in the composite membrane by incorporating sSiO2. The composite CAG–2% sSiO2 membrane exhibited a higher proton conductivity (6.4 mS/cm) than the pristine CA membrane. The homogeneous incorporation of SiO2 inorganic additives in the polymer matrix provided excellent mechanical properties. Due to the enhancement of the physicochemical, thermal, and mechanical properties, CAG–sSiO2 can effectively be considered an eco-friendly, low-cost, and efficient proton exchange membrane for enhancing MFC performance.</jats:p>

P. Arbter, W. Sabra, T. Utesch et al.

Engineering in Life Sciences • 2020

In this contribution, we studied the effect of electro‐fermentation on the butanol production of Clostridium pasteurianum strains by a targeted metabolomics approach. Two strains were examined: an electrocompetent wild type strain (R525) and a mutant strain (dhaB mutant) lacking formation of 1,3‐propanediol (PDO). The dhaB‐negative strain was able to grow on glycerol without formation of PDO, but displayed a high initial intracellular NADH/NAD ratio which was lowered subsequently by upregulation of the butanol production pathway. Both strains showed a 3–5 fold increase of the intracellular NADH/NAD ratio when exposed to cathodic current in a bioelectrochemical system (BES). This drove an activation of the butanol pathway and resulted in a higher molar butanol to PDO ratio for the R525 strain. Nonetheless, macroscopic electron balances suggest that no significant amount of electrons derived from the BES was harvested by the cells. Overall, this work points out that electro‐fermentation can be used to trigger metabolic pathways and improve product formation, even when the used microbe cannot be considered electroactive. Accordingly, further studies are required to unveil the underlying (regulatory) mechanisms.

A. Poladyan, S. Blbulyan, T. Semashko et al.

FEMS Microbiology Letters • 2020

Glycerol is an organic waste material, which can be used for production of microbial biomass and consequently serving valuable biocatalysts promoting generation of electric current in microbial fuel cell (MFC). [NiFe]-Hydrogenases (Hyd) of Escherichia coli and Ralstonia eutropha may be applied as potential anode biocatalysts in MFC. In this study, E. coli K12 whole cells or crude extracts and R. eutropha HF649 synthesizing Strep-tagged membrane-bound Hyd (MBH) were evaluated, as anode enzymes in the bioelectrochemical system. The samples were immobilized on the sensors with polyvinyl acetate support. Mediators like ferrocene and its derivatives (ferrocene-carboxy-aldehyde, ferrocene-carboxylic acid, methyl-ferrocene-methanol) were engaged. The maximal level of bioelectrocatalytic activity of Hyds was demonstrated at 500 mV voltage. Depending on the mediator and biocatalyst current strength varied from 5 μA to 42 μA. Introduction of ferrocene-carboxylic acid enhanced current strength: moreover, the current flow was directly correlated with H2 concentration. The maximal value (up to 150 μA) of current strength was achieved with a two-fold hydrogen supply. It may be inferred that Hyds are efficiently produced by E. coli and R. eutropha grown on glycerol, while ferrocene derivatives act as agents mediating electrochemical activity of Hyds.

T. Utesch, W. Sabra, Christin Prescher et al.

Biotechnology and Bioengineering • 2019

Microbial electrosynthesis or electro‐fermentation in bioelectrochemical systems (BES) have recently received much attention. Here, we demonstrate with the glycerol metabolism by Clostridium pasteurianum that H 2 from in situ water electrolysis, especially in combination with a redox mediator, provides a simple and flexible way for shifting product selectivity and enhancing product yield in the fermentation process. In particular, we report and quantify for the first time strictly different effects of Neutral Red (NR) and the barely studied redox mediator Brilliant Blue (BB) on the growth and product formation of C. pasteurianum grown on glycerol in a newly developed BES. We were able to switch the product formation pattern of C. pasteurianum with a concentration‐dependent addition of NR and BB under varied iron availability. Interestingly, NR and BB influenced the glycerol metabolism in a strictly opposite manner concerning the formation of the major products 1,3‐propanediol (1,3‐PDO) and n‐butanol (BuOH). Whereas, NR and iron generally enhance the formation of BuOH, BB favors the formation of 1,3‐PDO. In BES the metabolic shifts were enhanced, leading to a further increased yield by as high as 33% for BuOH in NR fermentations and 21% for 1,3‐PDO in BB fermentations compared with the respective controls. For the first time, the electron transfer mediated by these mediators and their recycle (recharge) were unambiguously quantified by excluding the overlapping effect of iron. BB has a higher capacity than NR and iron. The extra electron transfer by BB can account for as high as 30–75% of the total NAD + regeneration under certain conditions, contributing significantly to the product formation.

Jiahao Luo, Qianqian Yuan, Yufeng Mao et al.

Frontiers in Bioengineering and Biotechnology • 2022

Bioelectrochemical systems (BESs) based on Shewanella oneidensis MR-1 offer great promise for sustainable energy/chemical production, but the low rate of electron generation remains a crucial bottleneck preventing their industrial application. Here, we reconstructed a genome-scale metabolic model of MR-1 to provide a strong theoretical basis for novel BES applications. The model iLJ1162, comprising 1,162 genes, 1,818 metabolites and 2,084 reactions, accurately predicted cellular growth using a variety of substrates with 86.9% agreement with experimental results, which is significantly higher than the previously published models iMR1_799 and iSO783. The simulation of microbial fuel cells indicated that expanding the substrate spectrum of MR-1 to highly reduced feedstocks, such as glucose and glycerol, would be beneficial for electron generation. In addition, 31 metabolic engineering targets were predicted to improve electricity production, three of which have been experimentally demonstrated, while the remainder are potential targets for modification. Two potential electron transfer pathways were identified, which could be new engineering targets for increasing the electricity production capacity of MR-1. Finally, the iLJ1162 model was used to simulate the optimal biosynthetic pathways for six platform chemicals based on the MR-1 chassis in microbial electrosynthesis systems. These results offer guidance for rational design of novel BESs.

H. Roume, J. Arends, Camar Ameril et al.

Frontiers in Bioengineering and Biotechnology • 2016

Given the large amount of crude glycerol formed as a by-product in the biodiesel industries and the concomitant decrease in its overall market price, there is a need to add extra value to this biorefinery side stream. Upgrading can be achieved by new biotechnologies dealing with recovery and conversion of glycerol present in wastewaters into value-added products, aiming at a zero-waste policy and developing an economically viable process. In microbial bioelectrochemical systems (BESs), the mixed microbial community growing on the cathode can convert glycerol reductively to 1,3-propanediol (1,3-PDO). However, the product yield is rather limited in BESs compared with classic fermentation processes, and the synthesis of side-products, resulting from oxidation of glycerol, such as organic acids, represents a major burden for recovery of 1,3-PDO. Here, we show that the use of an enriched mixed-microbial community of glycerol degraders and in situ extraction of organic acids positively impacts 1,3-PDO yield and allows additional recovery of propionate from glycerol. We report the highest production yield achieved (0.72 mol1,3-PDO mol−1glycerol) in electricity-driven 1,3-PDO biosynthesis from raw glycerol, which is very close to the 1,3-PDO yield reported thus far for a mixed-microbial culture-based glycerol fermentation process. We also present a combined approach for 1,3-PDO production and propionate extraction in a single three chamber reactor system, which leads to recovery of additional 3-carbon compounds in BESs. This opens up further opportunities for an economical upgrading of biodiesel refinery side or waste streams.

F. Kubannek, Christopher Moß, Katharina J. Huber et al.

Frontiers in Energy Research • 2018

We investigated transformation pathways and determined rate constants in a continuously operated glycerol-fed bioelectrochemical system under chemostatic conditions by applying concentration pulses of various intermediates. Our methodology does not require the interruption of the continuous operation and is thus in principle suitable for elucidating processes in continuously operated bioreactors in industry as well as in laboratory studies. Specifically for the example of glycerol electrooxidation, pulse responses of current density and effluent concentrations reveal that glycerol is first fermented to acetate, which is then oxidized electrochemically by the anode respiring bacteria. Microbial community analysis confirms this division of labour with a bioanode dominated by Geobacter species 92.8 %) and a much more diverse fermenting community in the planktonic phase, containing mainly Desulfovibrio sp. (45.2 %) and Spiroaetales (18.1 %). Desulfovibrio and Geobacter species are identified as promising candidates for tailored communities for glycerol electro-oxidation. From an acetate concentration pulse experiment, growth rates and half saturation rate constants for the biofilm of K_S = 1.4 mol m^-3 and d(q_{max,Ac} X_{bf})/dt = 933 mmol m^-2 d^-2 are obtained. Furthermore, 1,3-propanediol and glycerol concentration pulse experiments show that the reaction from glycerol to 1,3-propanediol is reversed at high 1,3-propanediol concentrations. The presented methodology allows one to study pathways and extract rate constants through simple experiments in a running system without irreversibly altering the microbial community or destroying the biofilm.

Changman Kim, M. Y. Kim, I. Michie et al.

Biotechnology for Biofuels • 2017

Background3-Hydroxypropionic acid (3-HP) is an important platform chemical which can be produced biologically from glycerol. Klebsiella pneumoniae is an ideal biocatalyst for 3-HP because it can grow well on glycerol and naturally synthesize the essential coenzyme B12. On the other hand, if higher yields and titers of 3-HP are to be achieved, the sustained regeneration of NAD+ under anaerobic conditions, where coenzyme B12 is synthesized sustainably, is required.ResultsIn this study, recombinant K. pneumoniae L17 overexpressing aldehyde dehydrogenase (AldH) was developed and cultured in a bioelectrochemical system (BES) with the application of an electrical potential to the anode using a chronoamperometric method (+0.5 V vs. Ag/AgCl). The BES operation resulted in 1.7-fold enhancement of 3-HP production compared to the control without the applied potential. The intracellular NADH/NAD+ ratio was significantly lower when the L17 cells were grown under an electric potential. The interaction between the electrode and overexpressed AldH was enhanced by electron shuttling mediated by HNQ (2-hydroxy-1,4-naphthoquinone).ConclusionsEnhanced 3-HP production by the BES was achieved using recombinant K. pneumoniae L17. The quinone-based electron transference between the electrode and L17 was investigated by respiratory uncoupler experiments. This study provides a novel strategy to control the intracellular redox states to enhance the yield and titer of 3-HP production as well as other bioconversion processes.

Julia Pereira Narcizo, Lucca Bonjy Kikuti Mancilio, Matheus Pedrino et al.

Catalysts • 0

<jats:p>The ability of some bacteria to perform Extracellular Electron Transfer (EET) has been explored in bioelectrochemical systems (BES) to obtain energy or chemicals from pure substances or residual substrates. Here, a new pyoverdine-producing Pseudomonas aeruginosa strain was isolated from an MFC biofilm oxidizing glycerol, a by-product of biodiesel production. Strain EL14 was investigated to assess its electrogenic ability and products. In an open circuit system (fermentation system), EL14 was able to consume glycerol and produce 1,3-propanediol, an unusual product from glycerol oxidation in P. aeruginosa. The microbial fuel cell (MFC) EL14 reached a current density of 82.4 mA m−2 during the first feeding cycle, then dropped sharply as the biofilm fell off. Cyclic voltammetry suggests that electron transfer to the anode occurs indirectly, i.e., through a redox substance, with redox peak at 0.22 V (vs Ag/AgCl), and directly probably by membrane redox proteins, with redox peak at 0.05 V (vs Ag/AgCl). EL14 produced added-value bioproducts, acetic and butyric acids, as well as 1,3 propanediol, in both fermentative and anodic conditions. However, the yield of 1,3-PDO from glycerol was enhanced from 0.57 to 0.89 (mol of 1,3-PDO mol−1 of glycerol) under MFC conditions compared to fermentation. This result was unexpected, since successful 1,3-PDO production is not usually associated with P. aeruginosa glycerol metabolism. By comparing EL14 genomic sequences related to the 1,3-PDO biosynthesis with P. aeruginosa reference strains, we observed that strain EL14 has three copies of the dhaT gene (1,3-propanediol dehydrogenase a different arrangement compared to other Pseudomonas isolates). Thus, this work functionally characterizes a bacterium never before associated with 1,3-PDO biosynthesis, indicating its potential for converting a by-product of the biodiesel industry into an emerging chemical product.</jats:p>