Microbial Reactions Research Articles

Genomic fingerprints of the world's soil ecosystems.

Despite the explosion of soil metagenomic data, we lack a synthesized understanding of patterns in the distribution and functions of soil microorganisms. These patterns are critical to predictions of soil microbiome responses to climate change and resulting feedbacks that regulate greenhouse gas release from soils. To address this gap, we assay 1,512 manually curated soil metagenomes using complementary annotation databases, read-based taxonomy, and machine learning to extract multidimensional genomic fingerprints of global soil microbiomes. Our objective is to uncover novel biogeographical patterns of soil microbiomes across environmental factors and ecological biomes with high molecular resolution. We reveal shifts in the potential for (i) microbial nutrient acquisition across pH gradients; (ii) stress-, transport-, and redox-based processes across changes in soil bulk density; and (iii) greenhouse gas emissions across biomes. We also use an unsupervised approach to reveal a collection of soils with distinct genomic signatures, characterized by coordinated changes in soil organic carbon, nitrogen, and cation exchange capacity and in bulk density and clay content that may ultimately reflect soil environments with high microbial activity. Genomic fingerprints for these soils highlight the importance of resource scavenging, plant-microbe interactions, fungi, and heterotrophic metabolisms. Across all analyses, we observed phylogenetic coherence in soil microbiomes-more closely related microorganisms tended to move congruently in response to soil factors. Collectively, the genomic fingerprints uncovered here present a basis for global patterns in the microbial mechanisms underlying soil biogeochemistry and help beget tractable microbial reaction networks for incorporation into process-based models of soil carbon and nutrient cycling.IMPORTANCEWe address a critical gap in our understanding of soil microorganisms and their functions, which have a profound impact on our environment. We analyzed 1,512 global soils with advanced analytics to create detailed genetic profiles (fingerprints) of soil microbiomes. Our work reveals novel patterns in how microorganisms are distributed across different soil environments. For instance, we discovered shifts in microbial potential to acquire nutrients in relation to soil acidity, as well as changes in stress responses and potential greenhouse gas emissions linked to soil structure. We also identified soils with putative high activity that had unique genomic characteristics surrounding resource acquisition, plant-microbe interactions, and fungal activity. Finally, we observed that closely related microorganisms tend to respond in similar ways to changes in their surroundings. Our work is a significant step toward comprehending the intricate world of soil microorganisms and its role in the global climate.

Simulation of microbial transport and petroleum hydrocarbon compound biodegradation in a fracture–matrix coupled system

In-situ bioremediation technology is considered an ideal and environment-friendly approach for the largescale treatment of petroleum-contaminated soil. Most earlier studies on bioremediation have focused on the biostimulation techniques, which can enhance the biodegradation capabilities of indigenous bacteria, rather than on bioaugmentation involving the introduction of exogenous microorganisms. Additionally, contaminated soil sites typically contain both natural and artificial fractures. These fractures serve as preferential transport pathways, complicating the transport of bacteria and related solutes. This study proposes a mathematical model to simulate the transport of exogenous bacteria and electron acceptors during the degradation of petroleum hydrocarbon pollutants in a fractured aquifer system. The model incorporates the processes such as microbial convection, diffusion, adsorption, chemotaxis, growth, death, and microbial metabolic reactions. Simulation results demonstrate that considering microbial transport significantly affects the prediction of contaminant degradation, particularly with regard to the transport of electron acceptors. The growth rate of bacteria has an evident effect on the efficiency of contaminant remediation, and microbial chemotaxis can significantly enhance the degradation efficiency. The proposed mathematical model serves as a valuable tool for assessing the effectiveness of bioaugmentation strategies and can aid in the design and optimization of remediation efforts for contaminated and fractured aquifers.

Exploring the role of domesticated resistors in batch-mode microbial desalination cell

Microbial Desalination Cells (MDCs) are an electrochemical process that harnesses microbial reactions to simultaneously treat wastewater, generate power, and desalinate water. By utilizing microbial decomposition of organic pollutants in wastewater, MDCs offer a sustainable and energy-efficient alternative to conventional desalination technologies. The technical framework of MDCs emphasizes the integration of water-electricity principles, making them promising for future applications in seawater desalination, wastewater treatment, resource recovery, and water softening. This study investigates the impact of acclimation resistance, represented by four different domesticated resistors values of 1 kΩ, 100Ω, 51Ω, and 10Ω, on the performance of MDCs. Larger acclimation resistors exhibit higher power performance, with the case of 100Ω achieving a power density of 0.33 mA/m2 and the case of 1 kΩ achieving the highest current density of 1.90 mA/m2. Furthermore, the case with an acclimation resistance of 1 kΩ exhibits superior performance in terms of chemical oxygen demand (COD) removal, achieving a removal rate of 76.3% on day 1. Conversely, the case with an acclimation resistance of 10Ω demonstrates the best desalination performance, achieving a desalination rate of 9.0%. It should be noted that the optimal performance in terms of COD removal and desalination capacity varies due to the various operational mechanisms involved. . The findings of this study provide valuable insights for enhancing the performance of MDCs in future applications, enabling further improvements in their efficiency and effectiveness.

Overlapping Grid-Based Spectral Collocation Technique for Bioconvective Flow of MHD Williamson Nanofluid over a Radiative Circular Cylindrical Body with Activation Energy

The amalgamation of motile microbes in nanofluid (NF) is important in upsurging the thermal conductivity of various systems, including micro-fluid devices, chip-shaped micro-devices, and enzyme biosensors. The current scrutiny focuses on the bioconvective flow of magneto-Williamson NFs containing motile microbes through a horizontal circular cylinder placed in a porous medium with nonlinear mixed convection and thermal radiation, heat sink/source, variable fluid properties, activation energy with chemical and microbial reactions, and Brownian motion for both nanoparticles and microbes. The flow analysis has also been considered subject to velocity slips, suction/injection, and heat convective and zero mass flux constraints at the boundary. The governing equations have been converted to a non-dimensional form using similarity variables, and the overlapping grid-based spectral collocation technique has been executed to procure solutions numerically. The graphical interpretation of various pertinent variables in the flow profiles and physical quantities of engineering attentiveness is provided and discussed. The results reveal that NF flow is accelerated by nonlinear thermal convection, velocity slip, magnetic fields, and variable viscosity parameters but decelerated by the Williamson fluid and suction parameters. The inclusion of nonlinear thermal radiation and variable thermal conductivity helps to enhance the fluid temperature and heat transfer rate. The concentration of both nanoparticles and motile microbes is promoted by the incorporation of activation energy in the flow system. The contribution of microbial Brownian motion along with microbial reactions on flow quantities justifies the importance of these features in the dynamics of motile microbes.

Effect of Harvesting Time, Drying Method and Packaging of Cowpea Leaves on Microbial Contamination

After harvesting, cowpea leaves have high moisture content which exposes them to microbial growth. Drying is used to reduce the moisture and extend the shelf life. However, dried foods are susceptible to spoilage resulting from many microbial, biological, chemicals and physical reactions. After drying packaging materials used by farmers also expose the dried product to a range of microorganisms due to their different moisture retention capacity. This study aimed at prolonging the keeping quality of the dried cowpea leaves for use during off- season and coming up with information on the best and affordable packaging material that would ensure safety of dried leaves. Data was collected on fungal, bacteria and coliforms. The data was subjected to variance using Statistical Analysis System 9.2 edition and significantly different means separated using LSD at 5%. The combination of harvesting stage, drying method and packaging material significantly (p<0.05) influenced microbial load (bacterial and fungal), however no coliforms were observed. Open sun-dried cowpea leaves at 21 DAS, packaged in woven and aluminium foil reported a high number of bacterial and fungal counts compared to the kraft packaging. Oven dried cowpea leaves, harvested at 49 days after sowing (DAS), and in kraft paper resulted in the least bacterial and fungal contamination compared to those packaged in woven and aluminium foil. Sun drying and harvesting time after at 21, 35 and 49 DAS contained the highest bacterial and fungal contamination followed by solar drying and the least was recorded in oven drying method. This research shows that correct harvest stage, adoption of oven and solar drying methods and use of correct packaging material will prolong the shelf life of dried cowpea leaves therefore enhancing food security and food safety.

Dinickel enzyme evolved to metabolize the pharmaceutical metformin and its implications for wastewater and human microbiomes

Metformin is the first-line treatment for type II diabetes patients and a pervasive pollutant with more than 180 million kg ingested globally and entering wastewater. The drug's direct mode of action is currently unknown but is linked to effects on gut microbiomes and may involve specific gut microbial reactions to the drug. In wastewater treatment plants, metformin is known to be transformed by microbes to guanylurea, although genes encoding this metabolism had not been elucidated. In the present study, we revealed the function of two genes responsible for metformin decomposition (mfmA and mfmB) found in isolated bacteria from activated sludge. MfmA and MfmB form an active heterocomplex (MfmAB) and are members of the ureohydrolase protein superfamily with binuclear metal-dependent activity. MfmAB is nickel-dependent and catalyzes the hydrolysis of metformin to dimethylamine and guanylurea with a catalytic efficiency (kcat/KM) of 9.6 × 103 M-1s-1 and KM for metformin of 0.82 mM. MfmAB shows preferential activity for metformin, being able to discriminate other close substrates by several orders of magnitude. Crystal structures of MfmAB show coordination of binuclear nickel bound in the active site of the MfmA subunit but not MfmB subunits, indicating that MfmA is the active site for the MfmAB complex. Mutagenesis of residues conserved in the MfmA active site revealed those critical to metformin hydrolase activity and its small substrate binding pocket allowed for modeling of bound metformin. This study characterizes the products of the mfmAB genes identified in wastewater treatment plants on three continents, suggesting that metformin hydrolase is widespread globally in wastewater.

Surface crack treatment of concrete via nano-modified microbial carbonate precipitation

As a new concrete crack patching technology, microbial self-healing slurries offer favourable characteristics including non-pollution, ecological sustainability and good compatibility with concrete. In this paper, a nano-sio2-modified microbial bacteria liquid, combined with sodium alginate and polyvinyl alcohol, was used to prepare a nano-modified microbial self-healing slurry. This slurry was used to coat concrete under negative pressure in order to verify its restoration effect, and the micromorphology of the resulting microbial mineralization products was observed. The results revealed that patching the concrete using the nano-modified microbial slurry significantly improved its permeability, and increased its carbonization resistance by three times in comparison with the control group. Through a combination of Scanning electron microscopy (SEM) and X-ray diffraction (XRD) observation, it was determined that the microbial mineralization reaction products were mainly calcite crystals, which, integrated with the nano-sio2, sodium alginate and polyvinyl alcohol at the microscopic level, filled the internal pores of concrete, thus improving its durability.

Entropy optimization on magnetized radiative bioconvective flow of Carreau-Yasuda hybrid CNTs through a spherical surface in a non-Darcian porous medium with activation energy

This work inspects entropy generation and heat transfer induced by a bioconvection slip flow of nonlinear radiative Carreau-Yasuda hybrid nanofluid (NF) over a convectively heated sphere. Activation energy for microbes is contemplated in order to comprehend its contribution toward flow features. The original partial differential equations (PDEs) are rendered non-dimensional through appropriate conversions, and the resulting PDEs are solved using the overlapping grid spectral collocation algorithm. The impact of diverse flow factors on flow profiles, entropy generation, skin friction, heat, mass, and motile microbes transport rates is analyzed. Key outcomes reveal that hybrid NF flow demonstrates a supplementary indispensable feature in the operation of heat transport compared to mono NF flow. More entropy is generated in the system by using the hybrid NF model along with magnetic field, heat source, convective heating, nonlinear radiation, and viscous dissipation. Thermal fields and rate of heat transport are improved by including nonlinear radiative heat flux in the system. Mass and motile microbes transport rates are respectively enhanced by chemical and microbial reactions, but both quantities are reduced by activation energy. The effects of microbial reactions on flow quantities substantiate the significance of these features for the dynamics of microorganisms. The findings of this study can be useful in the upsurge of thermal performance of the working fluid and contribute toward the improvement of microbial fuel cell performance.

A novel mechanism for dissimilatory nitrate reduction to ammonium in Acididesulfobacillus acetoxydans.

The biological route of nitrate reduction has important implications for the bioavailability of nitrogen within ecosystems. Nitrate reduction via nitrite, either to ammonium (ammonification) or to nitrous oxide or dinitrogen (denitrification), determines whether nitrogen is retained within the system or lost as a gas. The acidophilic sulfate-reducing bacterium (aSRB) Acididesulfobacillus acetoxydans can perform dissimilatory nitrate reduction to ammonium (DNRA). While encoding a Nar-type nitrate reductase, A. acetoxydans lacks recognized nitrite reductase genes. In this study, A. acetoxydans was cultivated under conditions conducive to DNRA. During cultivations, we monitored the production of potential nitrogen intermediates (nitrate, nitrite, nitric oxide, hydroxylamine, and ammonium). Resting cell experiments were performed with nitrate, nitrite, and hydroxylamine to confirm their reduction to ammonium, and formed intermediates were tracked. To identify the enzymes involved in DNRA, comparative transcriptomics and proteomics were performed with A. acetoxydans growing under nitrate- and sulfate-reducing conditions. Nitrite is likely reduced to ammonia by the previously undescribed nitrite reductase activity of the NADH-linked sulfite reductase AsrABC, or by a putatively ferredoxin-dependent homolog of the nitrite reductase NirA (DEACI_1836), or both. We identified enzymes and intermediates not previously associated with DNRA and nitrosative stress in aSRB. This increases our knowledge about the metabolism of this type of bacteria and helps the interpretation of (meta)genome data from various ecosystems on their DNRA potential and the nitrogen cycle.IMPORTANCENitrogen is crucial to any ecosystem, and its bioavailability depends on microbial nitrogen-transforming reactions. Over the recent years, various new nitrogen-transforming reactions and pathways have been identified, expanding our view on the nitrogen cycle and metabolic versatility. In this study, we elucidate a novel mechanism employed by Acididesulfobacillus acetoxydans, an acidophilic sulfate-reducing bacterium, to reduce nitrate to ammonium. This finding underscores the diverse physiological nature of dissimilatory reduction to ammonium (DNRA). A. acetoxydans was isolated from acid mine drainage, an extremely acidic environment where nitrogen metabolism is poorly studied. Our findings will contribute to understanding DNRA potential and variations in extremely acidic environments.

Looking Back on My Life in Research over more than 40 Years

After graduating with a master's degree from Faculty of Pharmaceutical Sciences, Hokkaido University in 1983, I worked in medicinal chemistry for 37 years at a pharmaceutical company and 4 years at a university. On this occasion of my retirement, I would like to summarize the memorable reactions from my life in research over more than 40 years. This includes an overview of my drug discovery research at pharmaceutical companies covering practical and effective synthetic methods of key intermediates for renin inhibitors, 1β-methylcarbapenem, neurokinin receptor antagonists and sphingosine-1-phosphate receptor agonists. I have also described microbial transformation reactions for phosphorylation and glucuronidation, as well as antibacterial cyclic peptide and ogipeptins. During this time, two years of studying at the Scripps Research Institute and three years of working in India were also very valuable experiences. Finally, I have summarized the results of synthetic research on indole and azaindole derivatives conducted at the Health Sciences University of Hokkaido over a period of four years.

Effects of different thawing methods on the physicochemical properties and myofibrillar protein characteristics of Litopenaeus vannamei

Litopenaeus vannamei is a highly sought-after seafood, but its short shelf life makes it highly perishable due to microbial and chemical reactions. Freezing is a common technology used for extending the shelf life of shrimp. However, it is essential to undergo a thawing process before consuming or further processing frozen shrimp. In this study, the effects of different thawing methods, including immersion (IT), ultrasonic (UT), microwave (MT), refrigerator (RT), and air thawing (AT) on the qualitative parameters and protein denaturation of shrimp were investigated. The results showed that UT reduced fat oxidation and color degradation and was more effective than other thawing treatments like AT, IT, MT, and RT at retaining water. Based on the results of surface hydrophobicity, turbidity, particle size, and Zeta potential, UT reduced the aggregation and oxidation of myofibrillar proteins (MP) during the thawing process compared to other thawing methods. Utilizing UT also minimized the amount of harm that was done to MP secondary and tertiary structures during the thawing process. In conclusion, UT is a novel thawing technique to maintain the quality of shrimp meat quickly and effectively compared with other thawing methods, which is important for the quality of subsequent processing of frozen shrimp.

Temperature-dependent microbial reactions by indigenous microbes in bentonite under Fe(III)- and sulfate-reducing conditions

Bentonite is a promising buffer material for constructing spent nuclear fuel (SNF) repositories. However, indigenous microbes in bentonite can be introduced to the repository and subsequent sealing of the repository develops anoxic conditions over time which may stimulate fermentation and anaerobic respiration, possibly affecting bentonite structure and SNF repository stability. Moreover, the microbial activity in the bentonite can be impacted by the heat generated from radionuclides decay. Therefore, to investigate the temperature effect on microbial activities in bentonite, we created microcosms with WRK bentonil (a commercial bentonite) using lactate as the electron donor, and sulfate and/or ferrihydrite (Fe(III)) as electron acceptors with incubation at 18 ℃ and 50 ℃. Indigenous WRK microbes reduced sulfate and Fe(III) at both temperatures but with different rates and extents. Lactate was metabolized to acetate at both temperatures, but only to propionate at 18 ℃ during early-stage microbial fermentation. More Fe(III)-reduction at 18 ℃ but more sulfate-reduction at 50 ℃ was observed. Thermophilic and/or metabolically flexible microbes were involved in both fermentation and Fe(III)/sulfate reduction. Our findings illustrate the necessity of considering the influence of temperature on microbial activities when employing bentonite as an engineered buffer material in construction of SNF repository barriers.

Altering environmental conditions induce shifts in simulated deep terrestrial subsurface bacterial communities-Secretion of primary and secondary metabolites.

The deep terrestrial subsurface (DTS) harbours a striking diversity of microorganisms. However, systematic research on microbial metabolism, and how varying groundwater composition affects the bacterial communities and metabolites in these environments is lacking. In this study, DTS groundwater bacterial consortia from two Fennoscandian Shield sites were enriched and studied. We found that the enriched communities from the two sites consisted of distinct bacterial taxa, and alterations in the growth medium composition induced changes in cell counts. The lack of an exogenous organic carbon source (ECS) caused a notable increase in lipid metabolism in one community, while in the other, carbon starvation resulted in low overall metabolism, suggesting a dormant state. ECS supplementation increased CO2 production and SO4 2- utilisation, suggesting activation of a dissimilatory sulphate reduction pathway and sulphate-reducer-dominated total metabolism. However, both communities shared common universal metabolic features, most probably involving pathways needed for the maintenance of cell homeostasis (e.g., mevalonic acid pathway). Collectively, our findings indicate that the most important metabolites related to microbial reactions under varying growth conditions in enriched DTS communities include, but are not limited to, those linked to cell homeostasis, osmoregulation, lipid biosynthesis and degradation, dissimilatory sulphate reduction and isoprenoid production.

Comparing the response of the indigenous microbial community to crude oil amendment in oxic versus hypoxic conditions

IntroductionThe Caspian Sea is the world’s largest landlocked saline lake which lies between Europe and Asia. This region is particularly known for its large-scale oil reserves, pipelines, and drilling activities, which have contributed to the environmental decline of this lake. In addition to pollution from the petroleum industry, drainage from various river basins brings an influx of residential, industrial, and agricultural effluents that induce eutrophication and hypoxic conditions in deeper, colder waters, creating an oxygen gradient. The temperature and oxygen stratification in this environment has presented a unique opportunity to investigate the potential of the biodegradative processes carried out by the indigenous microbial community. We believe these indigenous microbes possess different metabolic capabilities to degrade oil as they adapted to declining oxygen concentrations and temperatures with increasing depths over a prolonged period. Hence, community structure and composition will vary with depth.MethodsMicrocosms were set up to observe the indigenous microbial reaction after a 60 ppm native crude oil amendment over 115 days. Surface water microcosms were incubated at 28ºC and aerated while deep water microcosms were incubated at 8ºC under anaerobic conditions. These two environmental conditions represent the temperature and oxygen extremes along the gradient and were selected as we try to simulate the indigenous community’s response to this oil contamination. DNA was extracted and amplified from these microcosms and sequenced. Bioinformatic analysis was performed to track changes in the abundance of taxa present and biodiversity over different time points to show the progression of community structure.ResultsAll microcosms showed the presence of hydrocarbon-degrading phyla, whose presence is consistent with other reports from oil-enriched environments. However, distinct communities were observed in oxic versus hypoxic microcosms.ConclusionOrders of Bacteria related to sulfate and nitrogen cycling were found in hypoxic microcosms, indicating a possible mechanism for the anaerobic biodegradation of crude oil. GC-MS analysis of initial and final microcosms also provided evidence of degradation of hydrocarbon fractions in both warm, oxic and cold, hypoxic conditions.

Microbiological insight into various underground gas storages in Vienna Basin focusing on methanogenic Archaea.

In recent years, there has been a growing interest in extending the potential of underground gas storage (UGS) facilities to hydrogen and carbon dioxide storage. However, this transition to hydrogen storage raises concerns regarding potential microbial reactions, which could convert hydrogen into methane. It is crucial to gain a comprehensive understanding of the microbial communities within any UGS facilities designated for hydrogen storage. In this study, underground water samples and water samples from surface technologies from 7 different UGS objects located in the Vienna Basin were studied using both molecular biology methods and cultivation methods. Results from 16S rRNA sequencing revealed that the proportion of archaea in the groundwater samples ranged from 20 to 58%, with methanogens being the predominant. Some water samples collected from surface technologies contained up to 87% of methanogens. Various species of methanogens were isolated from individual wells, including Methanobacterium sp., Methanocalculus sp., Methanolobus sp. or Methanosarcina sp. We also examined water samples for the presence of sulfate-reducing bacteria known to be involved in microbially induced corrosion and identified species of the genus Desulfovibrio in the samples. In the second part of our study, we contextualized our data by comparing it to available sequencing data from terrestrial subsurface environments worldwide. This allowed us to discern patterns and correlations between different types of underground samples based on environmental conditions. Our findings reveal presence of methanogens in all analyzed groups of underground samples, which suggests the possibility of unintended microbial hydrogen-to-methane conversion and the associated financial losses. Nevertheless, the prevalence of methanogens in our results also highlights the potential of the UGS environment, which can be effectively leveraged as a bioreactor for the conversion of hydrogen into methane, particularly in the context of Power-to-Methane technology.

Boosting power output in microbial fuel cells with microwave-assisted synthesis of hierarchical bimetallic anodes for enhanced extracellular electron transport

Microbial fuel cells (MFCs) are a promising technology that can generate electricity from various organic waste sources using bacteria as catalysts. However, the low power density of MFCs due to the inefficient extracellular electron transport (EET) remains a major challenge for MFCs. To address this challenge, researchers have been developing new anodes that can enhance the EET efficiency of MFCs. In this study, we report the fabrication of an efficient anode by embedding FeCo bimetallic nanoparticles on carbon cloth (FexCoy@CC) using a microwave-assisted synthesis and calcination process. We find that the Fe1Co1@CC anode demonstrates excellent electrocatalytic activity for electron transfer between bacteria and the anode. Furthermore, in mixed bacterial culture-based MFCs, the Fe1Co1@CC anode shows exceptional electrochemical performances, achieving a high-power density of 3220 mW m−2, a current density of 6.98 A m−2, and a Coulombic efficiency of 16.74 %. The remarkable performance is attributed to the high electronic conductivity provided, the enrichment of electrochemically active Geobacter species, and the EET efficiency enhancement of microbial redox reactions through FeCo bimetallic nanoparticles. This facile and cost-effective method demonstrates great potential for improving the performance of MFCs, which could lead to more efficient and sustainable wastewater treatment and green energy production.

Interplay between microbial activity and geochemical reactions during underground hydrogen storage in a seawater-rich formation

Subsurface hydrogen storage would be one of the main possible solutions for a successful energy transition in the future of world energy. However, hydrogen gas is an electron donor which may lead to microbial activity when storing hydrogen in the subsurface. Methanogenesis, acetogenesis, and sulfate reduction are the primary biological reactions that can lead to hydrogen loss through biochemical processes. This paper presents a novel bio-geochemical modelling approach which considers the kinetics of microbial reactions as well as the equilibrated geochemical reactions in the context of underground hydrogen storage. The findings demonstrate that the type of mineralogy and formation water composition may greatly influence biochemical reactions and thus potentially the storage/recovery performance of hydrogen. This study provides a detailed comparison and analysis of the behaviour occurring in calcite, dolomite, and quartz systems assuming the North Sea seawater composition as the in-situ brine. It is found that dolomite is the least favourable mineralogy in terms of hydrogen loss and hydrogen sulfide production, while calcite and quartz are better suited in a seawater-rich environment.

Effects of municipal waste compost on microbial biodiversity and energy production in terrestrial microbial fuel cells

Microbial Fuel Cells (MFCs) transform organic matter into electricity through microbial electrochemical reactions catalysed on anodic and cathodic half-cells. Terrestrial MFCs (TMFCs) are a bioelectrochemical system for bioelectricity production as well as soil remediation. In TMFCs, the soil is the ion-exchange electrolyte, whereas a biofilm on the anode oxidises organic matter through electroactive bacteria. Little is known of the overall microbial community composition in a TMFC, which impedes complete exploitation of the potential to generate energy in different soil types. In this context, an experiment was performed to reveal the prokaryotic community structure in single chamber TMFCs with soil in the presence and absence of a municipal waste compost (3% w/v). The microbial community was assessed on the anode and cathode and in bulk soil at the end of the experiment (54 days). Moreover, TMFC electrical performance (voltage and power) was also evaluated over the experimental period, varying the external resistance to improve performance. Compost stimulated soil microbial activity, in line with a general increase in voltage and power. Significant differences were observed in the microbial communities between initial soil conditions and TMFCs, and between the anode, cathode and bulk soil in the presence of the compost. Several electroactive genera (Bacillus, Fulvivirga, Burkholdeira and Geobacter) were found at the anode in the presence of compost. Overall, the use of municipal waste compost significantly increased the performance of the MFCs in terms of electrical power and voltage generated, not least thanks to the selective pressure towards electroactive bacteria on the anode.

The Effects of Aniline-Promoted Electron Shuttle-Mediated Goethite Reduction by Shewanella oneidensis MR-1 and theDegradation of Aniline

The biological reduction of Fe (III) is common in underground environments. This process not only affects the biogeochemical cycle of iron but also influences the migration and transformation of pollutants. Humic substances are considered effective strategies for improving the migration and transformation of toxic substances and enhancing the bioavailability of Fe (III). In this study, the electron shuttle anthraquinone-2-sulfonate (AQS) significantly promoted the bio-reduction of Fe (III). On this basis, different concentrations of aniline were added. The research results indicate that at an aniline concentration of 3 μM, the production of Fe (II) in the reaction system was 2.51 times higher compared to the microbial reaction group alone. Furthermore, the degradation of aniline was most effective in this group. The increased consumption of sodium lactate suggests that aniline, under the mediation of AQS, promoted the metabolism of Shewanella oneidensis MR-1 cells and facilitated the involvement of more electrons in the reduction process. After the reaction, the solid mineral Fe (II)-O content increased to 41.32%. This study provides insights into the reduction mechanism of Fe (III) in the complex environment of microorganisms, iron minerals, electron shuttles, and pollutants. It aims to offer a theoretical basis for the biodegradation of aromatic hydrocarbon pollutants.

Hydrogen-Driven Microbial Redox Reactions in Deep Geosystems

In the subsurface, biotic and abiotic processes can generate and consume hydrogen. Hydrogen has a low reduction potential and is thus a highly energetic electron donor when involved in sulfate, carbon dioxide or ferric iron reduction. Although known as important drivers for the deep biosphere, the contributions of different processes to hydrogen turnover in different geosystems still are not well understood. In context with the ongoing transformation to renewable energy resources, underground H2 storage (UHS) in deep porous or salt cavern systems came into focus. In situ microbial and geochemical reactions that consume H2 are highly relevant topics in deep biosphere research, and also are still a major uncertainty during UHS. Consequently, we studied the potential microbial hydrogen oxidation rates – combined with the possible production of metabolic products like H2S, acetic acid or CH4 - in formation fluids from natural gas fields and salt caverns, thereby considering the importance of in situ pressure and temperature conditions, fluid chemistry and mineral composition. In addition, more defined experiments were conducted with selected pure cultures representing important metabolic groups of deep biosphere microorganisms. Several original formation fluids showed immediate H2 consumption. Microorganisms oxidized hydrogen at relevant in situ pressure conditions (up to 100 bar) and tolerated dynamically changing pressure and temperature conditions. The microbial hydrogen oxidation rate was strongly dependent on H2 partial pressures and the availability of e.g., sulfate as a terminal electron acceptor. High-throughput sequencing of 16S rRNA gene amplicons indicated hydrogen oxidation by sulfate reducing bacteria to be the presumed process in the studied porous rock reservoir fluids. In addition, hydrogen turnover by methanogenic and acetogenic as well as iron-reducing microorganisms was investigated. Also, the importance of biotic reactions in relation to abiotic hydrogen turnover processes at mineral surfaces will be discussed.