Hydrogenotrophic Microorganisms Research Articles

Riboflavin-meditated interspecies electron transfer in a H2-based denitrifying biofilm

H2-based membrane biofilm reactors (MBfR) are effective for nitrogen removal, yet the interactions of microorganisms within the MBfR biofilms have received limited attention. In this study, we explored a flavin-mediated electron transport mechanism occurring between hydrogenotrophic microorganisms and non‑hydrogenotrophic denitrifying microorganisms in H2-based MBfR biofilms. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and electrochemical analysis confirmed riboflavin act as the sole potential redox mediator present in the system. Batch experiments demonstrated that riboflavin accelerates the denitrification process and that microorganisms can use reduced flavins as the sole electron donor to reduce nitrate. Metagenomic and metatranscriptomic analyses revealed increased expression of genes related to riboflavin biosynthesis and transport in hydrogenotrophic microorganisms, indicating endogenous riboflavin secretion into the medium. Our findings reveal the potential existence of a novel flavin-mediated electron transfer mechanism in the H₂-based denitrification process, enriching the understanding of interspecies interactions within MBfR biofilms. This study also provides a theoretical basis for efficient nitrogen removal through regulating interspecies electron transfer.

Synergizing sugarcane waste valorization: Optimization of two-stage anaerobic co-digestion for enhanced methane recovery and organic matter removal

Multiple strategies have been used in anaerobic digestion of effluents aiming to enhance the efficiency of the methane (CH4) recovery process, where co-digestion and the two-stage process emerge as prominent methods. In this context, this study aimed at evaluating the co-digestion of sugarcane vinasse and molasse in a two-stage process using anaerobic fluidized bed reactors (AFBR), verifying the effect of increasing the organic loading rate (OLR) (5–22.5 kg COD.m−3.d−1) and temperature in the second stage methanogenic reactor. Regarding the two-stage process, sugarcane vinasse and molasses fermentation demonstrated the maximum energy potential (E.P) of 57.08 kJ.d−1 (7.5 g COD.L−1). Regarding the methanogenic sequential reactors, organic matter removal reached high values (up to 84.5 % in a thermophilic sequential reactor (TSR); up to 84.5 % in a mesophilic sequential reactor (MSR)). The highest CH4 yield (MY) of 306.77 ± 38.84 mL CH4.g−1 COD rem was observed in MSR (9 kg COD.m−3.d−1). Meanwhile, the maximum value of MPR (3.8 ± 0.5 L CH4.L−1.d−1) was observed in TSR (21 kg COD.m−3.d−1). Regarding the Archaea domain, a predominance of hydrogenotrophic microorganisms could be identified, in which the genera Methanobacterium and Methanothermobacter were the most abundant in MSR and TSR, respectively. This study demonstrates that anaerobic digestion of sugarcane vinasse and molasses enhances anaerobic treatment using two-stage AFBRs. It not only produces CH4 but also generates hydrogen and high-value products through an acidogenic reactor. This research marks a significant advancement in managing sugarcane processing by-products, offering promising approaches to maximize biogas production and improve pollutant removal efficiency.

A one-dimensional diffusive transport model to evaluate H2S generation in salt caverns hydrogen storage sites

Salt caverns are considered a potential hydrogen storage site given the ductility, tightness, and chemical inertness of halite. In addition, unlike porous media, salt caverns require less cushion gas and allow more cycles of injection and production within a year. However, hydrogen is an electron donor for many hydrogenotrophic microorganisms including halophilic sulfate-reducing microbes (SRM) and hydrogen sulfide (H2S) can be generated in a cavern once sulfate and hydrogen become available in the aqueous phase. As salt deposits are often associated with large amounts of impurities such as anhydrite and gypsum, their dissolution during the leaching phase can release the required sulfate ions for SRMs to produce H2S once hydrogen diffuses and dissolves in the brine at the bottom of the cavern. In this study, a one-dimensional diffusive transport model was developed using PHREEQC to simulate sulfate reduction and H2S generation in a cavern at the gas-brine interface. The solution of Fick's diffusion equation was used to calculate the hydrogen concentration at each level of the 1D model while the kinetic rates of reactions were derived from reported experimental and field site observations of brine samples taken from salt caverns. The results obtained indicated that hydrogen consumption at the gas-brine interface can trigger H2S and methane formations. This is followed by a reduction in sulfate and carbonate concentration and a slight increase in pH due to the reduction of protons in the solution. It was also observed that the presence of Fe2+ ions can reduce the amount of the hydrogen sulfide production while Ca2+ ions slightly favour sulfate reduction due to the production of methane. Although the kinetic reaction rate of the reactions in the model is subject to a certain degree of uncertainty, the workflow and results this study can serve as a guide for the future storage of hydrogen in salt caverns.

Biomethane recovery through co-digestion of cheese whey and glycerol in a two-stage anaerobic fluidized bed reactor: Effect of temperature and organic loading rate on methanogenesis

Anaerobic digestion for CH4 recovery in wastewater treatment has been carried out with different strategies to increase process efficiency, among which co-digestion and the two-stage process can be highlighted. In this context, this study aimed at evaluating the co-digestion of cheese whey and glycerol in a two-stage process using fluidized bed reactors, verifying the effect of increasing the organic loading rate (OLR) (2–20 g-COD.L−1.d−1) and temperature (thermophilic and mesophilic) in the second stage methanogenic reactor. The mesophilic methanogenic reactor (R-Meso) (mean temperature of 22 °C) was more tolerant to high OLR and its best performance was at 20 g-COD.L−1.d−1, resulting in methane yield (MY) and methane production (MPR) of 273 mL-CH4.g-COD−1 and 5.8 L-CH4.L−1.d−1 (with 67% of CH4), respectively. Through 16S rRNA gene massive sequencing analysis, a greater diversity of microorganisms was identified in R-Meso than in R-Thermo (second stage methanogenic reactor, 55 °C). Firmicutes was the phyla with higher relative abundance in R-Thermo, while in R-Meso the most abundant ones were Proteobacteria and Bacteroidetes. Regarding the Archaea domain, a predominance of hydrogenotrophic microorganisms could be observed, being the genera Methanothermobacter and Methanobacterium the most abundant in R-Thermo and R-Meso, respectively. The two-stage system composed with a thermophilic acidogenic reactor + R-Meso was more adequate for the co-digestion of cheese whey and glycerol than the single-stage process, promoting increases of up to 47% in the energetic yield (10.3 kJ.kg-COD−1) and 14% in organic matter removal (90.5%).

Development of a rapid startup method of direct electron transfer-dominant methanogenic microbial electrosynthesis

The rapid startup of carbon dioxide reduction-methanogenic microbial electrosynthesis is crucial for its industrial application, and the development of cathode biofilm is the key to its industrialization. Based on the new discovery that biofilm formed by placing graphite felt in an anaerobic reactor was electroactive, with strong direct electron transfer and methanogenesis ability (24.52 mL/L/d), a new startup method was developed. The startup time was shortened by at least 20 days and charge transfer resistance was reduced by 4.45–10.78 times than common startup methods (inoculating cathode effluent or granular sludge into the cathode chamber). The new method enriched electroactive bacteria. Methanobacterium and Methanosaeta accounted for 62.04% and 34.96%, respectively. The common methods inoculating cathode effluent or granular sludge enriched hydrogenotrophic microorganisms (>95%) or Methanosaeta (54.10%) due to the local environments of cathode. This new rapid and easy startup method may support the scale-up of microbial electrosynthesis.

Direct and Indirect Methods for Studying Human Gut Microbiota

Aim: To review the main methods of intestinal microbiota studying.Key points. Currently, molecular genetic methods are used mainly for basic research and do not have a unified protocol for data analysis, which makes it difficult to implement them in clinical practice. Measurement of short chain fatty acids (SCFA) concentrations in plasma provides the data, which can serve as an indirect biomarker of the colonic microbiota composition. However, currently available evidence is insufficient to relate the obtained values (SCFA levels and ratio) to a particular disease with a high degree of certainty. Trimethylamine N-oxide (TMAO) levels in the blood plasma and urine can also reflect the presence of specific bacterial clusters containing genes Cut, CntA/CntB and YeaW/YeaX. Therefore, further studies are required to reveal possible correlations between certain disorders and such parameters as the composition of gut microbiota, dietary patterns and TMAO concentration. Gas biomarkers, i.e. hydrogen, methane and hydrogen sulphide, have been studied in more detail and are better understood as compared to other biomarkers of the gut microbiome composition and functionality. The main advantage of gas biomarkers is that they can be measured multiple times using non-invasive techniques. These measurements provide information on the relative proportion of hydrogenic (i.e. hydrogen producing) and hydrogenotrophic (i.e. methanogenic and sulfate-reducing) microorganisms. In its turn, this opens up the possibility of developing new approaches to correction of individual microbiota components.Conclusions. Integration of the data obtained by gut microbiota studies at the genome, transcriptome and metabolome levels would allow a comprehensive analysis of microbial community function and its interaction with the human organism. This approach may increase our understanding of the pathogenesis of various diseases as well open up new opportunities for prevention and treatment.

Testing novel multicomposite materials for electromethanogenesis

Electromethanogenesis is an innovative technology that uses a microbial electrochemical system to produce methane from CO2, in a power-to-gas (BEP2G) concept. The results of experimental tests of new and cost-effective carbonaceous materials for electrode are presented here. The study aims at optimizing electromethanogenesis processes at laboratory level in mesothermic condition. As part of the experiments, hydrogenotrophic microorganisms (Family Metanobacteriaceae of Archaea domains) were selected from a mixed consortium taken from a biogas digestate and inoculated in double-chamber bioelectrochemical systems. The maximum amount of methane produced was 0.3 - 0.8 mol/m2g (normalized to the cathode area) with carbon cloth electrodes. Aiming at improving the methane productivity, innovative materials for the electrodes were now studied, creating porous high-surface composites, and studying nitrogen carbons doped with Cu and hydroxyapatite (Multicomposite Cu@/HAP/C), as chemical catalysts for CO2 reduction (CO2RR). The description of the procedure for the Multicomposite Cu@/HAP/C production is reported in detail.

Mathematical Modeling of Bio Hydrogen Production in Microbial Electrolysis Cell Reactor

Mathematical modeling of biohydrogen production in microbial electrolysis cell reactor is discussed. This study explains the mathematical model for the production of hydrogen from a wastewater batch reactor, and it contains a system of non-linear equations. The non-linear differential equation of this model is solved by the Homotopy perturbation method. The approximate analytical expression of this model, concentration of substrate, anodophilic microorganisms, acetoclastic microorganism, hydrogenotrophic microorganisms, and Oxidized mediator are obtained. The effect of various values of the parameters on the reactions is discussed. The analytical solutions are also compared with simulation results and satisfactory the agreement is noted.

Extracellular Electron Uptake by Acetogenic Bacteria: Does H2 Consumption Favor the H2 Evolution Reaction on a Cathode or Metallic Iron?

Some acetogenic bacteria are capable of using solid electron donors, such as a cathode or metallic iron [Fe(0)]. Acetogens using a cathode as electron donor are of interest for novel applications such as microbial electrosynthesis, while microorganisms using Fe(0) as electron donor cause detrimental microbial induced corrosion. The capacity to use solid electron donors strongly differs between acetogenic strains, which likely relates to their extracellular electron transfer (EET) mechanism. Different EET mechanisms have been proposed for acetogenic bacteria, including a direct mechanism and a H2 dependent indirect mechanism combined with extracellular hydrogenases catalyzing the H2 evolution reaction on the cathode or Fe(0) surface. Interestingly, low H2 partial pressures often prevail during acetogenesis with solid electron donors. Hence, an additional mechanism is here proposed: the maintenance of low H2 partial pressures by microbial H2 consumption, which thermodynamically favors the H2 evolution reaction on the cathode or Fe(0) surface. This work elaborates how the H2 partial pressure affects the H2 evolution onset potential and the H2 evolution rate on a cathode, as well as the free energy change of the anoxic corrosion reaction. In addition, the H2 consumption characteristics, i.e., H2 threshold (thermodynamic limit for H2 consumption) and H2 consumption kinetic parameters, of acetogenic bacteria are reviewed and evidence is discussed for strongly different H2 consumption characteristics. Different acetogenic strains are thus expected to maintain different H2 partial pressures on a cathode or Fe(0) surface, while those that maintain lower H2 partial pressures (lower H2 threshold, higher H2 affinity) more strongly increase the H2 evolution reaction. Consequently, I hypothesize that the different capacities of acetogenic bacteria to use solid electron donors are related to differences in their H2 consumption characteristics. The focus of this work is on acetogenic bacteria, but similar considerations are likely also relevant for other hydrogenotrophic microorganisms.

Breath Test Gas Patterns in Inflammatory Bowel Disease with Concomitant Irritable Bowel Syndrome-Like Symptoms: A Controlled Large-Scale Database Linkage Analysis.

Breath testing (BT) has gained interest for diagnosing small intestinal bacterial overgrowth (SIBO) in IBD patients with irritable bowel syndrome (IBS) overlap. We aim to characterize the rate of SIBO and BT gas patterns in IBD patients with IBS-like symptoms compared to non-IBD patients. A database of 14,847 consecutive lactulose BTs was developed from patients with IBS-like symptoms between November 2005 and October 2013. BTs were classified as normal, H2 predominant, CH4 predominant, and flatline based on criteria established from the literature. BT data linkage with electronic health records and chart review identified IBD patients along with disease phenotype, location, severity, and antibiotic response. Poisson loglinear model evaluated differences in gas patterns between the two groups. After excluding patients with repeat breath tests, we identified 486 IBD and 10,505 non-IBD patients with at least one BT. Positive BT was present in 57% (n = 264) of IBD patients. Crohn's disease (odds ratio (OR) 0.21, [95% confidence interval (CI) 0.11-0.38]) and ulcerative colitis (OR 0.39, [95% CI 0.22-0.70]) patients were less likely to produce excess CH4. IBD patients were more likely to have flatline BT (OR 1.82, [95% CI 1.20-2.77]). In IBD patients with SIBO, 57% improved symptomatically with antibiotics. In a cohort of IBD patients with IBS-like symptoms, a high rate of patients had positive BT and symptomatic improvement with antibiotics. In IBD, methanogenesis is suppressed and flatline BT is more frequent, suggesting excess hydrogenotrophic bacteria. These findings suggest methanogenic and hydrogenotrophic microorganisms as potential targets for microbiome-driven biomarkers and therapies.

Unique Differences in Breath Test Gas Patterns in Inflammatory Bowel Disease (IBD) Compared to Non-IBD Patients: A Large-Scale Database Linkage Analysis

Introduction: Breath testing (BT) has gained interest for diagnosing small intestinal bacterial overgrowth (SIBO) in IBD patients with overlapping irritable bowel syndrome (IBS)-like symptoms. We aimed to characterize BT gas patterns in IBD patients compared to non-IBD patients and assess antibiotic response. Methods: A database of 14,847 consecutive lactulose BTs performed between November 2005 and October 2013 was developed from patients with IBS-like symptoms. Repeated BTs were excluded using probabilistic record linkage. BTs were classified into 5 categories: Normal: CH4 <10 parts per million (ppm) and H2 rise <20ppm within 90 min. H2predominant: CH4 <10ppm and H2 rise >20 ppm within 90 min, CH4 predominant: CH4 ≥10 ppm, Flatline: CH4 =0 ppm and H2≤3 ppm with variation ≤1 ppm within 120 min, Equivocal: H2 >20ppm at baseline. BT data was linked to our electronic health records to identify IBD patients and their disease course through manual chart review. Response to antibiotics was determined by reported improvement in symptoms. Poisson loglinear model was used assess differences in gas patterns between IBD and non-IBD patients. Results: After probabilistic linkage, we identified 455 IBD and 10,505 non-IBD patients with BT. Demographics and disease phenotypes are summarized in Table 1 and Table 2. SIBO was present in 58% (n=264) of IBD patients with IBS overlap. (Fig 1) Patients with Crohn's disease (CD) (effect size (ES) -1.48, [95% confidence interval (CI) -0.84- -2.13], p<0.001) and ulcerative colitis (UC) (ES -0.80, [95%CI -0.19- -1.14], p=0.01) were significantly less likely to produce excessive CH4 compared to non-IBD patients. When combined, IBD patients were more likely to be flatliner than non-IBD patients (ES 0.49, [95%CI 0.04-0.95], p=0.03). CH4predominant SIBO was significantly more prevalent in UC patients with constipation than other gas patterns (50%, p=0.001). In IBD patients with SIBO, 57% responded to antibiotics independent of disease activity, location, and behavior.679_A Figure 1. Cohort demographics of non-IBD patients compared to IBD patients.Conclusion: IBD patients with ongoing IBS-like symptoms have high prevalence of SIBO and demonstrate symptomatic improvement with antibiotics. Methanogenesis is suppressed in IBD patients. Flatline BT is more prevalent in IBD patients, suggesting excessive hydrogenotrophic bacteria. These findings suggest CH4 producing and hydrogenotrophic microorganisms as potential therapeutic targets. Future prospective studies are needed to validate these findings.679_B Figure 2. Disease phenotype of IBD patients.679_C Figure 3. Comparison of breath test patterns of CD, UC and non-IBD patients. Methanogenesis is significantly suppressed in CD and UC patients with IBS-like symptoms compared to non-IBD patients. There is no statistically significant difference between breath test patterns of CD and UC patients.

Abundance and Diversity of Hydrogenotrophic Microorganisms in the Infant Gut before the Weaning Period Assessed by Denaturing Gradient Gel Electrophoresis and Quantitative PCR.

Delivery mode (natural vs. cesarean) and feeding type (breast vs. formula feeding) are relevant factors for neonatal gut colonization. Biomolecular methods have shown that the ecological structure of infant microbiota is more complex than previously proposed, suggesting a relevant presence of unculturable bacteria. It has also been postulated that among unculturable bacteria, hydrogenotrophic populations might play a key role in infant health. Sulfate-reducing bacteria (SRB), acetogens, and methanogenic archaea use hydrogenotrophic pathways within the human colon. However, to date, few studies have reported detection of hydrogenotrophic microorganisms in newborns, possibly because of limitations on available group-specific, culture-independent quantification procedures. In the present work, we analyzed 16 fecal samples of healthy babies aged 1–6 months by means of quantitative PCR (qPCR) targeting the 16S rRNA or metabolic functional genes and by denaturing gradient gel electrophoresis (DGGE). qPCR data showed quantifiable levels of methanogens, SRB, and acetogens in all samples, indicating that the relative abundances of these microbial groups were not affected by delivery mode (natural vs. caesarian). DGGE revealed a high prevalence of the Blautia genus within the acetogenic bacteria despite strong interindividual variability. Our preliminary results suggest that hydrogenotrophic microorganisms, which have been a neglected group to date, should be included in future ecological and metabolic studies evaluating the infant intestinal microbiota.

Evidence for Seismogenic Hydrogen Gas, a Potential Microbial Energy Source on Earth and Mars.

The oxidation of molecular hydrogen (H2) is thought to be a major source of metabolic energy for life in the deep subsurface on Earth, and it could likewise support any extant biosphere on Mars, where stable habitable environments are probably limited to the subsurface. Faulting and fracturing may stimulate the supply of H2 from several sources. We report the H2 content of fluids present in terrestrial rocks formed by brittle fracturing on fault planes (pseudotachylites and cataclasites), along with protolith control samples. The fluids are dominated by water and include H2 at abundances sufficient to support hydrogenotrophic microorganisms, with strong H2 enrichments in the pseudotachylites compared to the controls. Weaker and less consistent H2 enrichments are observed in the cataclasites, which represent less intense seismic friction than the pseudotachylites. The enrichments agree quantitatively with previous experimental measurements of frictionally driven H2 formation during rock fracturing. We find that conservative estimates of current martian global seismicity predict episodic H2 generation by Marsquakes in quantities useful to hydrogenotrophs over a range of scales and recurrence times. On both Earth and Mars, secondary release of H2 may also accompany the breakdown of ancient fault rocks, which are particularly abundant in the pervasively fractured martian crust. This study strengthens the case for the astrobiological investigation of ancient martian fracture systems. Deep biosphere-Faults-Fault rocks-Seismic activity-Hydrogen-Mars. Astrobiology 16, 690-702.

Microbial Methane Production Associated with Carbon Steel Corrosion in a Nigerian Oil Field.

Microbially influenced corrosion (MIC) in oil field pipeline systems can be attributed to many different types of hydrogenotrophic microorganisms including sulfate reducers, methanogens and acetogens. Samples from a low temperature oil reservoir in Nigeria were analyzed using DNA pyrotag sequencing. The microbial community compositions of these samples revealed an abundance of anaerobic methanogenic archaea. Activity of methanogens was demonstrated by incubating samples anaerobically in a basal salts medium, in the presence of carbon steel and carbon dioxide. Methane formation was measured in all enrichments and correlated with metal weight loss. Methanogens were prominently represented in pipeline solids samples, scraped from the inside of a pipeline, comprising over 85% of all pyrosequencing reads. Methane production was only witnessed when carbon steel beads were added to these pipeline solids samples, indicating that no methane was formed as a result of degradation of the oil organics present in these samples. These results were compared to those obtained for samples taken from a low temperature oil field in Canada, which had been incubated with oil, either in the presence or in the absence of carbon steel. Again, methanogens present in these samples catalyzed methane production only when carbon steel was present. Moreover, acetate production was also found in these enrichments only in the presence of carbon steel. From these studies it appears that carbon steel, not oil organics, was the predominant electron donor for acetate production and methane formation in these low temperature oil fields, indicating that the methanogens and acetogens found may contribute significantly to MIC.

Laboratory-scale bioaugmentation relieves acetate accumulation and stimulates methane production in stalled anaerobic digesters.

An imbalance between acidogenic and methanogenic organisms during anaerobic digestion can result in increased accumulation of volatile fatty acids, decreased reactor pH, and inhibition of methane-producing Archaea. Most commonly the result of organic input overload or poor inoculum selection, these microbiological and biochemical changes severely hamper reactor performance, and there are a few tools available to facilitate reactor recovery. A small, stable consortium capable of catabolizing acetate and producing methane was propagated in vitro and evaluated as a potential bioaugmentation tool for stimulating methanogenesis in acidified reactors. Replicate laboratory-scale batch digesters were seeded with a combination of bioethanol stillage waste and a dairy manure inoculum previously observed to result in high volatile fatty acid accumulation and reactor failure. Experimental reactors were then amended with the acetoclastic consortium, and control reactors were amended with sterile culture media. Within 7 days, bioaugmented reactors had significantly reduced acetate accumulation and the proportion of methane in the biogas increased from 0.2 ± 0 to 74.4 ± 9.9 % while control reactors showed no significant reduction in acetate accumulation or increase in methane production. Organisms from the consortium were enumerated using specific quantitative PCR assays to evaluate their growth in the experimental reactors. While the abundance of hydrogenotrophic microorganisms remained stable during the recovery period, an acetoclastic methanogen phylogenetically similar to Methanosarcina sp. increased more than 100-fold and is hypothesized to be the primary contributor to reactor recovery. Genomic sequencing of this organism revealed genes related to the production of methane from acetate, hydrogen, and methanol.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-015-7058-3) contains supplementary material, which is available to authorized users.

Biogas production from different size fractions separated from solid waste and the accompanying changes in the community structure of methanogenic Archaea

There is a need to study the biogas production of waste substrates using routine tests because the characteristics of these substrates influence the kinetics of methane fermentation. In this study, biogas production from different size fractions of solid waste (0–20mm, 20–40mm, 20–80mm, and 40–100mm) was measured using a 90 days gas production test in mesophilic conditions. How the methanogenic community structure during fermentation corresponds to the chemical composition of the size fractions was determined.Biogas production strongly negatively correlated with the biogas production rate constants (kbiogas) due to differences in the availability of organic substances. Microorganisms in the 20–80mm size fraction produced the most biogas (252±11L/kg TS, kbiogas=0.16±0.04day−1), which had the highest methane content (ca. 50%), probably because this size fraction had the highest organics content and the most diverse microbial community. In this size fraction, Methanosarcinaceae (acetoclastic microorganisms) and Methanobacteriaceae (hydrogenotrophic microorganisms) were more abundant than in other fractions. The 0–20mm size fraction produced the least amount of biogas (65±8L/kg TS); however, its kbiogas was the highest (0.32±0.05day−1), suggesting that organic matter was easily accessible to the microorganisms. Although the 0–20mm size fraction is considered to be a mineral fraction that can be used for recultivation, the results of this study suggest that this fraction should be processed first to avoid environmental contamination.

Iron corrosion induced by nonhydrogenotrophic nitrate-reducing Prolixibacter sp. strain MIC1-1.

Microbiologically influenced corrosion (MIC) of metallic materials imposes a heavy economic burden. The mechanism of MIC of metallic iron (Fe(0)) under anaerobic conditions is usually explained as the consumption of cathodic hydrogen by hydrogenotrophic microorganisms that accelerates anodic Fe(0) oxidation. In this study, we describe Fe(0) corrosion induced by a nonhydrogenotrophic nitrate-reducing bacterium called MIC1-1, which was isolated from a crude-oil sample collected at an oil well in Akita, Japan. This strain requires specific electron donor-acceptor combinations and an organic carbon source to grow. For example, the strain grew anaerobically on nitrate as a sole electron acceptor with pyruvate as a carbon source and Fe(0) as the sole electron donor. In addition, ferrous ion and l-cysteine served as electron donors, whereas molecular hydrogen did not. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain MIC1-1 was a member of the genus Prolixibacter in the order Bacteroidales. Thus, Prolixibacter sp. strain MIC1-1 is the first Fe(0)-corroding representative belonging to the phylum Bacteroidetes. Under anaerobic conditions, Prolixibacter sp. MIC1-1 corroded Fe(0) concomitantly with nitrate reduction, and the amount of iron dissolved by the strain was six times higher than that in an aseptic control. Scanning electron microscopy analyses revealed that microscopic crystals of FePO4 developed on the surface of the Fe(0) foils, and a layer of FeCO3 covered the FePO4 crystals. We propose that cells of Prolixibacter sp. MIC1-1 accept electrons directly from Fe(0) to reduce nitrate.

Effect of fumarate reducing bacteria on in vitro rumen fermentation, methane mitigation and microbial diversity

The metabolic pathways involved in hydrogen (H(2)) production, utilization and the activity of methanogens are the important factors that should be considered in controlling methane (CH(4)) emissions by ruminants. H(2) as one of the major substrate for CH(4) production is therefore should be controlled. One of the strategies on reducing CH(4) is through the use of hydrogenotrophic microorganisms such as fumarate reducing bacteria. This study determined the effect of fumarate reducing bacteria, Mitsuokella jalaludinii, supplementation on in vitro rumen fermentation, CH(4) production, diversity and quantity. M. jalaludinii significantly reduced CH(4) at 48 and 72 h of incubation and significantly increased succinate at 24 h. Although not significantly different, propionate was found to be highest in treatment containing M. jalaludinii at 12 and 48 h of incubation. These results suggest that supplementation of fumarate reducing bacteria to ruminal fermentation reduces CH(4) production and quantity, increases succinate and changes the rumen microbial diversity.

Production of Hydrogen from α-1,4- and β-1,4-Linked Saccharides by Marine Hyperthermophilic Archaea

Nineteen hyperthermophilic heterotrophs from deep-sea hydrothermal vents, plus the control organism Pyrococcus furiosus, were examined for their ability to grow and produce H₂ on maltose, cellobiose, and peptides and for the presence of the genes encoding proteins that hydrolyze starch and cellulose. All of the strains grew on these disaccharides and peptides and converted maltose and peptides to H₂ even when elemental sulfur was present as a terminal electron acceptor. Half of the strains had at least one gene for an extracellular starch hydrolase, but only P. furiosus had a gene for an extracellular β-1,4-endoglucanase. P. furiosus was serially adapted for growth on CF11 cellulose and H₂ production, which is the first reported instance of hyperthermophilic growth on cellulose, with a doubling time of 64 min. Cell-specific H₂ production rates were 29 fmol, 37 fmol, and 54 fmol of H₂ produced cell⁻¹ doubling⁻¹ on α-1,4-linked sugars, β-1,4-linked sugars, and peptides, respectively. The highest total community H₂ production rate came from growth on starch (2.6 mM H₂ produced h⁻¹). Hyperthermophilic heterotrophs may serve as an important alternate source of H₂ for hydrogenotrophic microorganisms in low-H₂ hydrothermal environments, and some are candidates for H₂ bioenergy production in bioreactors.

Influence of the Composition of the Cellulolytic Flora on the Development of Hydrogenotrophic Microorganisms, Hydrogen Utilization, and Methane Production in the Rumens of Gnotobiotically Reared Lambs

We investigated the influence of the composition of the fibrolytic microbial community on the development and activities of hydrogen-utilizing microorganisms in the rumens of gnotobiotically reared lambs. Two groups of lambs were reared. The first group was inoculated with Fibrobacter succinogenes, a non-H(2)-producing species, as the main cellulolytic organism, and the second group was inoculated with Ruminococcus albus, Ruminococcus flavefaciens, and anaerobic fungi that produce hydrogen. The development of hydrogenotrophic bacterial communities, i.e., acetogens, fumarate and sulfate reducers, was monitored in the absence of methanogens and after inoculation of methanogens. Hydrogen production and utilization and methane production were measured in rumen content samples incubated in vitro in the presence of exogenous hydrogen (supplemented with fumarate or not supplemented with fumarate) or in the presence of ground alfalfa hay as a degradable substrate. Our results show that methane production was clearly reduced when the dominant fibrolytic species was a non-H(2)-producing species, such as Fibrobacter succinogenes, without significantly impairing fiber degradation and fermentations in the rumen. The addition of fumarate to the rumen contents stimulated H(2) utilization only by the ruminal microbiota inoculated with F. succinogenes, suggesting that these communities could play an important role in fumarate reduction in vivo.