Showing papers on "Methanogen published in 2007"

Molecular characterization of microbial communities in deep coal seam groundwater of northern Japan

Abstract: We investigated microbial methanogenesis and community structure based on 16S rRNA gene sequences from a coal seam aquifer located 843–907 m below ground level in northern Japan; additionally, we studied the δ13C and δ2H (δD) of coal-bed gases and other physicochemical parameters. Although isotopic analysis suggested a thermocatalytic origin for the gases, the microbial activity and community structure strongly implied the existence of methanogenic microbial communities in situ. Methane was generated in the enrichment cultures of the hydrogenotrophic and methylotrophic microorganisms obtained from coal seam groundwater. Methanogen clones dominated the archaeal 16S rRNA gene libraries and were mostly related to the hydrogenotrophic genus Methanoculleus and the methylotrophic genus Methanolobus. Bacterial 16S rRNA gene libraries were dominated by the clones related to the genera Acetobacterium and Syntrophus which have a symbiotic association with methanogens. LIBSHUFF analysis revealed that N2 gas injected into the coal seam (for enhanced methane production) does not affect the coverage of archaeal and bacterial populations. However, amova analysis does provide evidence for a change in the genetic diversity of archaeal populations that are dominated by methanogens. Therefore, N2 injection into the coal seam might affect the cycling of matter by methanogens in situ.

Salinity Constraints on Subsurface Archaeal Diversity and Methanogenesis in Sedimentary Rock Rich in Organic Matter

Abstract: The diversity of microorganisms active within sedimentary rocks provides important controls on the geochemistry of many subsurface environments. In particular, biodegradation of organic matter in sedimentary rocks contributes to the biogeochemical cycling of carbon and other elements and strongly impacts the recovery and quality of fossil fuel resources. In this study, archaeal diversity was investigated along a salinity gradient spanning 8 to 3,490 mM Cl− in a subsurface shale rich in CH4 derived from biodegradation of sedimentary hydrocarbons. Shale pore waters collected from wells in the main CH4-producing zone lacked electron acceptors such as O2, NO3−, Fe3+, or SO42−. Acetate was detected only in high-salinity waters, suggesting that acetoclastic methanogenesis is inhibited at Cl− concentrations above ∼1,000 mM. Most-probable-number series revealed differences in methanogen substrate utilization (acetate, trimethylamine, or H2/CO2) associated with chlorinity. The greatest methane production in enrichment cultures was observed for incubations with salinity at or close to the native pore water salinity of the inoculum. Restriction fragment length polymorphism analyses of archaeal 16S rRNA genes from seven wells indicated that there were links between archaeal communities and pore water salinity. Archaeal clone libraries constructed from sequences from 16S rRNA genes isolated from two wells revealed phylotypes similar to a halophilic methylotrophic Methanohalophilus species and a hydrogenotrophic Methanoplanus species at high salinity and a single phylotype closely related to Methanocorpusculum bavaricum at low salinity. These results show that several distinct communities of methanogens persist in this subsurface, CH4-producing environment and that each community is adapted to particular conditions of salinity and preferential substrate use and each community induces distinct geochemical signatures in shale formation waters.

Isolation of Key Methanogens for Global Methane Emission from Rice Paddy Fields: a Novel Isolate Affiliated with the Clone Cluster Rice Cluster I

Abstract: Despite the fact that rice paddy fields (RPFs) are contributing 10 to 25% of global methane emissions, the organisms responsible for methane production in RPFs have remained uncultivated and thus uncharacterized. Here we report the isolation of a methanogen (strain SANAE) belonging to an abundant and ubiquitous group of methanogens called rice cluster I (RC-I) previously identified as an ecologically important microbial component via culture-independent analyses. To enrich the RC-I methanogens from rice paddy samples, we attempted to mimic the in situ conditions of RC-I on the basis of the idea that methanogens in such ecosystems should thrive by receiving low concentrations of substrate (H(2)) continuously provided by heterotrophic H(2)-producing bacteria. For this purpose, we developed a coculture method using an indirect substrate (propionate) in defined medium and a propionate-oxidizing, H(2)-producing syntroph, Syntrophobacter fumaroxidans, as the H(2) supplier. By doing so, we significantly enriched the RC-I methanogens and eventually obtained a methanogen within the RC-I group in pure culture. This is the first report on the isolation of a methanogen within RC-I.

Diversity of Archaea in Marine Sediments from Skan Bay, Alaska, Including Cultivated Methanogens, and Description of Methanogenium boonei sp. nov.

Abstract: Methanogenesis in cold marine sediments is a globally important process leading to methane hydrate deposits, cold seeps, physical instability of sediment, and atmospheric methane emissions. We employed a multidisciplinary approach that combined culture-dependent and -independent analyses with geochemical measurements in the sediments of Skan Bay, Alaska (53°N, 167°W), to investigate methanogenesis there. Cultivation-independent analyses of the archaeal community revealed that uncultivated microbes of the kingdoms Euryarchaeota and Crenarchaeota are present at Skan Bay and that methanogens constituted a small proportion of the archaeal community. Methanogens were cultivated from depths of 0 to 60 cm in the sediments, and several strains related to the orders Methanomicrobiales and Methanosarcinales were isolated. Isolates were psychrotolerant marine-adapted strains and included an aceticlastic methanogen, strain AK-6, as well as three strains of CO2-reducing methanogens: AK-3, AK7, and AK-8. The phylogenetic positions and physiological characteristics of these strains are described. We propose a new species, Methanogenium boonei, with strain AK-7 as the type strain.

Identification and Quantification of Methanogenic Archaea in Adult Chicken Ceca

Abstract: By using molecular methods for the identification and quantification of methanogenic archaea in adult chicken ceca, 16S rRNA genes of 11 different phylotypes, 10 of which were 99% similar to Methanobrevibacter woesei, were found. Methanogen populations, as assessed by cultivation, and the 16S rRNA copy number were between 6.38 and 8.23 cells/g (wet weight) and 5.50 and 7.19 log10/g (wet weight), respectively.

Functionally distinct genes regulated by hydrogen limitation and growth rate in methanogenic Archaea

Abstract: The use of molecular hydrogen as electron donor for energy generation is a defining characteristic of the hydrogenotrophic methanogens, an ancient group that dominates the phylum Eury archaeota. We present here a global study of changes in mRNA abundance in response to hydrogen availability for a hydrogenotrophic methanogen. Cells of Methanococcus maripaludis were grown by using continuous culture to deconvolute the effects of hydrogen limitation and growth rate, and microarray analyses were conducted. Hydrogen limitation markedly increased mRNA levels for genes encoding enzymes of the methanogenic pathway that reduce or oxidize the electron-carrying deazaflavin, coenzyme F420. F420-dependent redox functions in energy-generating metabolism are characteristic of the methanogenic Archaea, and the results show that their regulation is distinct from other redox processes in the cell. Rapid growth increased mRNA levels of the gene for an unusual hydrogenase, the hydrogen-dependent methylenetetrahydromethanopterin dehydrogenase.

Effects of cattle husbandry on abundance and activity of methanogenic archaea in upland soils.

Abstract: In the present study, we tested the hypothesis that animal treading associated with a high input of organic matter would favour methanogenesis in soils used as overwintering pasture. Hence, methane emissions and methanogen populations were examined at sections with different degree of cattle impact in a Farm in South Bohemia, Czech Republic. In spring, methane emission positively corresponded to the gradient of animal impact. Applying phospholipid etherlipid analysis, the highest archaeal biomass was found in section severe impact (SI), followed by moderate impact (MI) and no impact. The same trend was observed for the methanogens as showed by real-time quantitative PCR analyses of methyl coenzyme M reductase (mcrA) genes. The detection of monounsaturated isoprenoid side chain hydrocarbons (i20:1) indicated the presence of acetoclastic methanogens in the cattle-impacted sites. This result was corroborated by the phylogenetic analysis of mcrA gene sequences obtained from section SI, which showed that 33% of the analysed clones belonged to the genus Methanosarcina. The majority of the sequenced clones (41%) showed close affiliations with uncultured rumen archaeons. This leads to the assumption that a substantial part of the methanogenic community in plot SI derived from the grazing cattle itself. Compared to the spring sampling, in autumn, a significant reduction in archaeal biomass and number of copies of mcrA genes was observed mainly for section MI. It can be concluded that after 5 months without cattle impact, the severely impact section maintained its methane production potential, whereas the methane production potential under moderate impact returned to background values.

Analysis of Methanogen Diversity in the Rumen Using Temporal Temperature Gradient Gel Electrophoresis: Identification of Uncultured Methanogens

Abstract: A temporal temperature gradient gel electrophoresis (TTGE) method was developed to determine the diversity of methanogen populations in the rumen. Tests with amplicons from genomic DNA from 12 cultured methanogens showed single bands for all strains, with only two showing apparently comigrating bands. Fingerprints of methanogen populations were analyzed from DNA extracted from rumen contents from two cattle and four sheep grazing pasture. For one sheep, dilution cultures selective for methanogens were grown and the culturable methanogens in each successive dilution examined by TTGE. A total of 66 methanogen sequences were retrieved from bands in fingerprints and analyzed to reveal the presence of methanogens belonging to the Methanobacteriales, the Methanosarcinales, and to an uncultured archaeal lineage. Twenty-four sequences were most similar to Methanobrevibacter ruminantium, five to Methanobrevibacter smithii, four to Methanosphaera stadtmanae, and for three, the nearest match was Methanimicrococcus blatticola. The remaining 30 sequences did not cluster with sequences from cultured archaea, but when combined with published novel sequences from clone libraries formed a monophyletic lineage within the Euryarchaeota, which contained two previously unrecognized clusters. The TTGE bands from this lineage showed that the uncultured methanogens had significant population densities in each of the six rumen samples examined. In cultures of dilutions from one rumen sample, TTGE examination revealed these methanogens at a level of at least 105 g−1. Band intensities from low-dilution cultures indicated that these methanogens were present at similar densities to Methanobrevibacter ruminantium-like methanogens, the sole culturable methanogens in high dilutions (106–10−10 g−1). It is suggested that the uncultured methanogens together with Methanobrevibacter spp. may be the predominant methanogens in the rumen. The TTGE method presented in this article provides a new opportunity for characterizing methanogen populations in the rumen microbial ecosystem.

Microbial diversity and methanogenic potential in a high temperature natural gas field in Japan

Abstract: Microbial diversity and methanogenic potential in formation water samples from a dissolved-in-water type gas field were investigated by using 16S rRNA gene libraries and culture-based methods. Two formation water samples (of 46 and 53 degrees C in temperature) were obtained from a depth of 700 to 800 m. Coenzyme F(420)-autofluorescence indicated that 10(3)-10(4) cells per ml of active methanogens were present, accounting for at least 10% of the total cell count. The 16S rRNA gene sequence analysis indicated that the diversity of Archaea and Bacteria of the two samples was quite limited; i.e., the archaeal libraries were dominated by the sequences related to Methanobacterium formicicum and Methanothermobacter thermautotrophicus, and the bacterial libraries were dominated by the sequences related to Hydrogenophilus and Deferribacter. Of the methanogenic substrates tested using the formation water-based medium, only H(2)-CO(2) gave rise to methane formation. Those dominant archaeal and bacterial genera have the potential to use hydrogen for growth at the in situ temperatures, suggesting that the formation water of the Pliocene strata in the gas field has been provided with hydrogen, probably from underneath the strata, and thus on-going active methanogenesis has been occurring to date.

Detection of methane and quantification of methanogenic archaea in faeces from young broiler chickens using real-time PCR

Abstract: Aims: To detect the presence of methanogens in the faeces of broiler chicks during the first 2 weeks of age. Methods and Results: Chicken faecal samples from 120 broiler chicks were incubated for methane gas formation and methanogenic archaea were analysed using real-time PCR. The copy number of the order Methanobacteriales 16S rDNA gene in chicken faeces when the broilers were 3–12 days of age, litter and house flies collected in the bird house ranged from 4·19 to 5·51 log10 g−1 wet weight. The number of positive methane culture tubes increased from 25% to 100% as the birds aged. Conclusions: Methanogens were successfully detected in faecal samples from 3- to 12-day-old broilers, as well as litter and house flies using real-time PCR. The copy number of methanogenic 16S rDNA gene in these samples was also similar to the number observed in litter and house flies. Significance and Impact of the Study: The same methanogens consistently appeared in chicken faeces a few days after birth. Detection of the methanogenic bacteria in litter and house flies implicated them as potential environmental sources for methanogen colonization in broiler chicks.

Methanogen Diversity in Deep Subsurface Gas-Associated Water at the Minami-Kanto Gas Field in Japan

Abstract: Methanogen diversity and methanogenic potential in formation water obtained from the Minami-kanto gas field in Japan were investigated by using 16S rRNA gene libraries and culture-based enrichment methods, respectively. This region is the largest gas field that produces natural gases of dissolved-in-water type in Japan. Although the microbial population density was below statistical quantification limits (1 × 104 cells ml−1), autofluorescent coccoid and rod-shaped cells indicative of methanogens were observed. The represented genera in the archaeal 16S rRNA genes libraries were comprised of Methanobacterium, Methanospirillum, Methanocalculus, Methanococcus, Methanolobus and Methanosaeta. The dominant archaeal sequences were related to the hydrogenotrophic methanogens in the genus Methanobacterium. Of the methanogenic substrates tested using the formation water-based medium,H2-CO2 yielded the highest methane production. These results strongly suggest that the formation water of the Pleistocene strata in th...

Effect of dilution rate on the microbial structure of a mesophilic butyrate-degrading methanogenic community during continuous cultivation.

Abstract: We constructed two mesophilic anaerobic chemostats that were continuously fed with synthetic wastewater containing butyrate as the sole source of carbon and energy. Steady-state conditions were achieved at dilution rates between 0.025 and 0.7 day−1. Butyrate, fed into the chemostat, was almost completely mineralized to CH4 and CO2 at dilution rates below 0.5 day−1. The butyrate-degrading methanogenic communities in the chemostats at dilution rates between 0.025 and 0.7 day−1 were monitored based on the 16S rRNA gene, using molecular biological techniques including clone library analysis, denaturing gradient gel electrophoresis, and quantitative real-time polymerase chain reaction. The aceticlastic methanogen Methanosaeta and the hydrogenotrophic methanogen Methanoculleus dominated in methanogens at low dilution rates, whereas the aceticlastic methanogen Methanosaeta, Methanosarcina, the hydrogenotrophic methanogen Methanoculleus, and Methanospirillum dominated at high dilution rates. Bacteria affiliated with the family Syntrophaceae in the phylum Proteobacteria predominated at the low dilution rate of 0.025 day−1, whereas bacteria affiliated with the phylum Firmicutes and Candidate division OP3 predominated at high dilution rates. A significant quantity of bacteria closely related to the genus Syntrophomonas was detected at high dilution rates. Dilution rate showed an apparent effect on archaeal and bacterial communities in the butyrate-fed chemostats.

The effect of methanogen growth on mineral substrates: will Ni markers of methanogen‐based communities be detectable in the rock record?

Abstract: Methanogens, thought to be present on early Earth, have a high requirement for Ni, suggesting that Ni utilization could be a potential biosignature for methanogens if enhanced Ni extraction from surrounding minerals accompanies methanogenic growth. To test the potential for such Ni extraction from minerals by methanogens, Ni release from Ni-containing silicate glass was measured in Ni-free growth medium in the presence of the methanogen Methanothermobacter thermoautotrophicus (average pH ∼ 7.0) and observed to be higher than an abiotic control (average pH ∼ 6.8). However, batch dissolution experiments and a siderophore assay indicate that cell exudates such as siderophores, low molecular weight organic acids, or lysates accompanying cell death are not responsible for the observed increase in Ni release rate. In addition, scanning electron microscopy (SEM) shows little to no evidence of direct microbe‐mineral interactions such as biofilms or pitting. Instead, comparison with abiotic experiments suggests that changes in pH due to CO 2 uptake may be responsible for enhanced dissolution in the presence of metabolizing cells. These results document that methanogens may not preferentially extract Ni from surrounding minerals although they may indirectly affect mineral reaction rates that are pH sensitive. Thus identifiable Ni biosignatures may not exist in the rock record to document the presence of methanogens on early Earth or Mars.

Molecular monitoring of microbial population dynamics during operational periods of anaerobic hybrid reactor treating cassava starch wastewater.

Abstract: This study characterized the microbial community and population dynamics in an anaerobic hybrid reactor (AHR) treating cassava starch wastewater. Methanogens and nonmethanogens were followed during the start-up and operation of the reactor, and linked to operational and performance data. Biomass samples taken from the sludge bed and packed bed zones of the AHR at intervals throughout the operational period were examined by 16S rRNA fluorescence in situ hybridization (FISH). The start-up seed and the reactor biomass were sampled during the feeding of the wastewater with a chemical oxygen demand (COD) value of 8 g L−1 and a hydraulic retention time (HRT) of 8 days. These samples were characterized by the predominance of cells with long-rod morphology similar to Methanosaeta spp. Following a sharp operational change, accomplished by increasing the COD concentration of the organic influent from 8 to 10 g L−1 and reducing the HRT from 8 to 5 days, there was a doubling of the organic loading rate, a reduction of the COD removal efficiency, as well as decreased methane content in the biogas and an accumulation of total volatile acids in the reactor. Moreover, this operational change resulted in a significant population shift from long-rod Methanosaeta-like cells to tetrad-forming Methanosarcina-like cells. The distributions of microbial populations involved in different zones of the AHR were determined. The results showed that nonmethanogens became the predominant population in both sludge and the packed bed zone. However, the percentage of methanogens in the packed bed zone was higher than that in the sludge bed zone. This higher percentage of methanogens was likely caused by the fact that the packed bed zone provided a suitable environmental condition with an appropriate nutrient availability for methanogen growth.

Anaerobic degradation of nonylphenol in soil

Abstract: This study investigated the effects of various factors on the anaerobic degradation of nonylphenol (NP) in soil. The results show that the optimal pH for NP degradation was 7.0 and that the degradation rate was enhanced when the temperature was increased. The addition of compost enhanced NP degradation. The individual addition of the electron donors lactate, acetate, and pyruvate inhibited NP degradation. The high-to-low order of NP degradation rates under three anaerobic conditions was sulfate-reducing conditions > methanogenic conditions > nitrate-reducing conditions. The results show that sulfate-reducing bacteria, methanogen, and eubacteria are involved in the anaerobic degradation of NP, with sulfate-reducing bacteria being a major component of the soil. Of the anaerobic strains isolated from the soil samples, strain AT3 expressed the best ability to biodegrade NP.

Study on the Isolation and Growth Condition of Methanogen

Abstract: Two methanogen strains were isolated from methane fermenting liquor by using Hungate obligate anaerobic technique with methanol,formate and acetate as carbon and energy source.They emit blue-green fluorescence when observed by fluorogenic microscope.Their colonies in roll tubes are irregular round and white or a little yellow.In addition,the effect of different pH value and temperature of the growth of the methanogen was studied.The methanogen's optimum growth pH value is 7.0 and can range from 6.5 to 8.0,and the optimum growth temperature is 35 ℃,the results indicated that they were sensitive to the change of pH value and temperature,so a steady circumstance is needed.

Analysis of Methanogen Membrane Lipids and Its Application to Sanhu Depression,Qaidam basin

Abstract: Biogenic gas is the product of methanogen in anaoxic environment.Its formation and occurrence is controlled by the distribution of methanogen.The present method in studying the distribution of methanogen is MPN(numbers of methanogen).Because methanogen is strict with its environment,especially with the occurrence of oxygen,trivial change should disturb the bacterial collects and make the number different from the reality.Otherwise,collection of the fresh groundwater is difficult for us.All those make MPN turn to be hard to be dealed with.The concentration of some special biomarkers of methanogen,especially its core membrane components,could reflect the distribution of methanogen for a time.This method is simple and easy to operate,could make up the deficiency.In this paper,the distribution of archaeol,the core membrane structure components,is analyzed in the sediment from two wells in the Sanhu depression Qaidam basin.The results showed a good relationship between methanogen and salinity.In high salt area,the activity of methanogens was depressed in the shallow(above 1000m),and then turned to active up to 2000m.While in the surrounding area like Sebei 1 area,the salinity of sediment is much lower,the depression of methanogen in the shallow is slight that make methanogen mainly concentrate above 1000m and is low below 1000m.In the final,combined with the sediment palaeoenvironment and salinity of the sediment,the activation of methanogen in Sanhu depression is characterized.

Development of Bioreactors for Enrichment of Chemolithotrophic Methanogen and Methane Production

Abstract: A gas-circulating bioreactor was used for enrichment of autotrophic methanogens. Mixture of hydrogen and carbon dioxide (5:1) was used as a sole energy and carbon source. Anaerobic digestive sludge isolated from wastewater treatment system was inoculated into the gas-circulating bioreactor. The enrichment of two chemolithotrophic methanogens, Methanobacterium curvum and Methanobacterium oryzae was accomplished in the gas-circulating bioreactor. The enriched bacteria were cultivated in a bioreactor equipped with hollow-fiber hydrogen-supplying system (hollow-fiber bioreactor), and a hybrid-type bioreactor equipped with hollow-fiber hydrogen-supplying system and electrochemical redox control system. The methane productivity was maximally 30% (V/V) in the hollow-fiber bioreactors and 50% (V/V) in the hybrid-type bioreactor.

Characterization of Microbial Community Structure and Diversity, Present in Thermophilic Anaerobic Digestion of Waste-Activated Sludge

Abstract: The microbial community structures present in the thermophilic anaerobic digestion (TAD) of waste-activated sludge (WAS) and WAS were analyzed with molecular biological techniques including polymerase chain reaction-denature gradient gel electrophoresis (PCR-DGGE), real-time PCR, and cloning analysis. No significant differences in the microbial community structures present in TAD were observed among three reactors operated with hydraulic retention times of 10, 20 and 30 days. The microbial community present in TAD had less diversity than that present in WAS, and the sequences obtained in WAS were not present in TAD by the cloning analysis. In the TAD bacterial clone library, 97.5% of the total clones belonged to Firmicutes and 73.1% belonged to Coprothermobacter. Real-time PCR and cloning analyses revealed that the number of Methanosarcina thermophila, which is an acetoclastic methanogen, was larger than that of Methanoculleus thermophilus, which is a hydrogenotrophic methanogen, in terms of the numbers of copies of 16S rDNA.

Elementary metal, enclosed in a packaging, useful for process stabilization in a device for biological methane production

Abstract: Elementary metals or mixture of two or more elementary metals that are enclosed in a packaging. Independent claims are included for: (1) a methanogen mixed culture that is enclosed in a packaging; (2) a packaging comprising an elementary metal or mixture of two or more elementary metal and/or a methanogen mixed culture; (3) the use of elementary metal for process stabilization in a device for biological methane production; (4) a procedure for the process stabilization, in a device, for the biological methane production comprising providing a device with biomass and methanogen mixed culture, adding the elementary metal and fermenting; and (5) a device for the biological methane production comprising a filling device for adding elementary metal and/or methanogen mixed culture.

The Ech Hydrogenase is Important for Growth of D vulgaris with Hydrogen

Abstract: Author(s): Stolyar, S.M.; Wall, J.; Stahl, D.A. | Abstract: One objective of the Virtual Institute for Microbial Stress and Survival (VIMSS) and the Environmental Stress Pathway Project (ESPP) is to determine the genetic and physiological basis for cooperative and competitive interactions among environmental microbial populations of relevance to the DOE. The ESPP Applied Environmental Core (AEC) and Functional Genomics Core (FGC) have identified a number of genes that may participate in cooperative interactions between sulfate reducers and methanogens under low sulfate conditions. Specifically, the gram-negative Deltaproteobacterium D. vulgaris is able to grow in the absence of an electron acceptor via syntrophic growth with hydrogenotrophic organisms. Despite decades of research, energy conservation in D. vulgaris is not well understood. The presence of multiple hydrogenases, including those located in the periplasm in all studied Desulfovibrio strains - and the observation that hydrogen is produced and then consumed during growth of D. vulgaris Miyazaki with lactate and sulfate (Tsuji aYagi, 1980) - lead to the formulation of the hydrogen cycling hypothesis as a mechanism for energy conservation (Odom a Peck, 1981). The availability of a completed genome sequence of D. vulgaris Hildenborough has since revealed genes for at least six different hydrogenases: four periplasmic and two cytoplasmic. Although several have been partially characterized biochemically and genetically, their roles in D. vulgaris under different growth conditions is not well understood. We examined the growth and metabolite production of an echA (DVU0434) D vulgaris Hidenborough mutant under three different growth conditions: i) in medium amended with lactate and sulfate and ii) in medium amended with acetate, hydrogen and sulfate, and iii) in coculture the hydrogenotrophic methanogen M. maripaludis, lacking an electron acceptor. On lactate, the mutant demonstrated a comparable growth rate and yield to the wild type strain, but evolved more hydrogen as measured by its accumulation in the headspace during growth in batch culture. In a medium containing 5 mM acetate and an atmosphere of H2/CO2 (80:20), growth of the mutant was severely impaired relative to the wild type. A coculture consisting of the mutant strain and a hydrogenotrophic methanogen (M. maripaludis) demonstrated only slightly reduced growth rate and biomass relative to the wild type. Although this suggested some role in energy conservation, the more obvious phenotype was its greatly limited growth in monoculture with acetate, hydrogen and sulfate. Thus, the available data suggest that the primary role of the Ech Hydrogenase is oxidation of hydrogen during sulfate respiration, possibly also contributing to the production of reduced ferredoxin required for conversion of Acetyl CoA to pyruvate by pyruvate oxidoreductase, as was previously demonstrated for the homologous hydrogenases in M. barkeri and M. maripaludis (Meuer et al., 2002; Porat et al., 2006).