Methanogenic Strain Research Articles

Genetic, physiological and biochemical features of the methanogenic strain Methanosarcina spelaei LB-BZ-1 isolated from oil-saturated bottom sediments of Lake Baikal

A culture of irregular cocci with a diameter of 0.7-1.5 μm, capable of producing methane when growing on a mixture of H2/CO2 gases, methanol, mono-, di- and trimethylamines, was isolated from the bottom sediments of the Bolshaya Zelenovskaya oil-methane seep. On the basis of physiological-biochemical, phenotypic and genetic characteristics, it was found that the microorganism obtained in pure culture is a new strain of Methanosarcina spelaei LB-BZ-1, which has differences from the type strain in a number of parameters, including the ability to produce methane from acetate

Methanomethylophilus alvi gen. nov., sp. nov., a Novel Hydrogenotrophic Methyl-Reducing Methanogenic Archaea of the Order Methanomassiliicoccales Isolated from the Human Gut and Proposal of the Novel Family Methanomethylophilaceae fam. nov.

The methanogenic strain Mx-05T was isolated from the human fecal microbiome. A phylogenetic analysis based on the 16S rRNA gene and protein marker genes indicated that the strain is affiliated with the order Methanomassiliicoccales. It shares 86.9% 16S rRNA gene sequence identity with Methanomassiliicoccus luminyensis, the only member of this order previously isolated. The cells of Mx-05T were non-motile cocci, with a diameter range of 0.4-0.7 μm. They grew anaerobically and reduced methanol, monomethylamine, dimethylamine, and trimethylamine into methane, using H2 as an electron donor. H2/CO2, formate, ethanol, and acetate were not used as energy sources. The growth of Mx-05T required an unknown medium factor(s) provided by Eggerthella lenta and present in rumen fluid. Mx-05T grew between 30 °C and 40 °C (optimum 37 °C), over a pH range of 6.9-8.3 (optimum pH 7.5), and between 0.02 and 0.34 mol.L-1 NaCl (optimum 0.12 mol.L-1 NaCl). The genome is 1.67 Mbp with a G+C content of 55.5 mol%. Genome sequence annotation confirmed the absence of the methyl branch of the H4MPT Wood-Ljungdahl pathway, as described for other Methanomassiliicoccales members. Based on an average nucleotide identity analysis, we propose strain Mx-05T as being a novel representative of the order Methanomassiliicoccales, within the novel family Methanomethylophilaceae, for which the name Methanomethylophilus alvi gen. nov, sp. nov. is proposed. The type strain is Mx-05T (JCM 31474T).

Beyond corrosion: development of a single cell-ICP-ToF-MS method to uncover the process of microbiologically influenced corrosion.

The development of the microbiologically influenced corrosion (MIC)-specific inductively coupled plasma-time of flight-mass spectrometry (ICP-ToF-MS) analytical method presented here, in combination with the investigation of steel-MIC interactions, contributes significantly to progress in instrumental MIC analysis. For this, a MIC-specific staining procedure was developed, which ensures the analysis of intact cells. It allows the analysis of archaea at a single cell level, which is extremely scarce compared to other well-characterized organisms. The detection method revealed elemental selectivity for the corrosive methanogenic strain Methanobacterium-affiliated IM1. Hence, the possible uptake of individual elements from different steel samples was investigated and results showed the cells responded at a single-cell level to the different types of supplemented elements and displayed the abilities to uptake chromium, vanadium, titanium, cobalt, and molybdenum from solid metal surfaces. The methods developed and information obtained will be used in the future to elucidate underlying mechanisms, compliment well-developed methods, such as SEM-EDS, and develop novel material protection concepts.

Isolation of a Novel Thermophilic Methanogen and the Evolutionary History of the Class Methanobacteria.

Simple SummaryThe methanogenesis pathway via methanogens dates back to the Hadean or Archaean Earth. These methanogens are considered to have a thermophilic origin and are presently ubiquitously distributed across anaerobic environments. The class Methanobacteria comprises methanogens that are found extensively in geothermal environments, such as hot springs and hydrothermal vents, and their evolutionary history and how they adapted to different temperatures remain unclear. In this study, we isolated a novel species of the class Methanobacteria from a natural hot spring in Tengchong, China. This species can produce methane, utilizing hydrogen and carbon dioxide, at 65 °C. In addition, we found that members of the class Methanobacteria originated in a geothermal niche and then evolved to adapt to ambient temperatures; during this process, thermal adaptation genes were lost and a wide range of metabolic genes were acquired. This research on methanogen evolution will help us understand how life originated in geothermal environments and then spread extensively across present-day Earth.Methanogens can produce methane in anaerobic environments via the methanogenesis pathway, and are regarded as one of the most ancient life forms on Earth. They are ubiquitously distributed across distinct ecosystems and are considered to have a thermophilic origin. In this study, we isolated, pure cultured, and completely sequenced a single methanogen strain DL9LZB001, from a hot spring at Tengchong in Southwest China. DL9LZB001 is a thermophilic and hydrogenotrophic methanogen with an optimum growth temperature of 65 °C. It is a putative novel species, which has been named Methanothermobacter tengchongensis—a Class I methanogen belonging to the class Methanobacteria. Comparative genomic and ancestral analyses indicate that the class Methanobacteria originated in a hyperthermal environment and then evolved to adapt to ambient temperatures. This study extends the understanding of methanogens living in geothermal niches, as well as the origin and evolutionary history of these organisms in ecosystems with different temperatures.

Methanofollis propanolicus sp. nov., a novel archaeal isolate from a Costa Rican oil well that uses propanol for methane production

A novel methanogenic strain, CaP3V-MF-L2AT, was isolated from an exploratory oil well from Cahuita National Park, Costa Rica. The cells were irregular cocci, 0.8–1.8 μm in diameter, stained Gram-negative and were motile. The strain utilized H2/CO2, formate and the primary and secondary alcohols 1-propanol and 2-propanol for methanogenesis, but not acetate, methanol, ethanol, 1-butanol or 2-butanol. Acetate was required as carbon source. The novel isolate grew at 25–40 °C, pH 6.0–7.5 and 0–2.5% (w/v) NaCl. 16S rRNA gene sequence analysis revealed that the strain is affiliated to the genus Methanofollis. It shows 98.8% sequence similarity to its closest relative Methanofollis ethanolicus. The G + C content is 60.1 mol%. Based on the data presented here type strain CaP3V-MF-L2AT (= DSM 113321T = JCM 39176T) represents a novel species, Methanofollis propanolicus sp. nov.

High-Pressure Microfluidics for Ultra-Fast Microbial Phenotyping.

Here, we present a novel methodology based on high-pressure microfluidics to rapidly perform temperature-based phenotyping of microbial strains from deep-sea environments. The main advantage concerns the multiple on-chip temperature conditions that can be achieved in a single experiment at pressures representative of the deep-sea, overcoming the conventional limitations of large-scale batch metal reactors to conduct fast screening investigations. We monitored the growth of the model strain Thermococcus barophilus over 40 temperature and pressure conditions, without any decompression, in only 1 week, whereas it takes weeks or months with conventional approaches. The results are later compared with data from the literature. An additional example is also shown for a hydrogenotrophic methanogen strain (Methanothermococcus thermolithotrophicus), demonstrating the robustness of the methodology. These microfluidic tools can be used in laboratories to accelerate characterizations of new isolated species, changing the widely accepted paradigm that high-pressure microbiology experiments are time-consuming.

Converting Carbon Dioxide in to Methane Gas and Enhance Oil Recovery by using Biotechnology Process

Using biotechnology in petroleum industry has many advantages .for example , Microbiologically Enhanced Oil Recovery (MEOR) increase of the productivity of the oil field and decrease the viscosity of the crude oil . It's known that atmosphere has considerable amount of CO2 gas as a result of industrial activities (crude oil production). CO2 gas plays a role in increasing atmosphere temperature and causing global warming. Bioremediation is a viable Biotechnology function for Re-producing depleted wells and global warming. It means Bioremediation uses metabolic adaptation of microorganism, a promising approach, using this technique employs of Methanogenic bacteria to convert CO2 gas in to CH4. Therefore turns carbon dioxide in to carbon which is added to crude oil (so contribute decrease the viscosity for heavy crude oil, This mechanism is a part of the promotion of oil production.it is apart an operation EOR. and Second reacts with Hydrogen by Bacteria to produce methane gas. The aim study, advantage this method increase production. and removal global warming. In this review, we discuss the role of Methanogenic bacteria in transforming CO2 gas into methane gas , that it has a role in crude oil production . Methanogenic bacteria have an important role in petroleum industry and environment during decreasing CO2 amount in the atmosphere and increasing reservoir pressure. MEOR technology uses strains that have a role in crude oil production; these bacterial strains produce biogases (Methane) that increase reservoir pressure. In this study, six strains were isolated from Rumaila oilfield, south of Iraq. These strains were identified based on microscopic and morphological observations. These strains were Methanogenic bacteria. The main part of this study includes identification of bacteria that can consume CO2 gas and making continual lab experiments to isolate and determine the best genus to do this process in oil field. Experiments were done in specific bio-labs for two years, Methanogenic bacteria strains were isolated by using specific selective growth media. The second part of this study is using these strains for bioremediation process of oil wells, which includes providing anaerobic conditions for these strains to transform CO2 gas to methane . Morphological and microscopic observations were conducted to these strains and showed the best kind of these strains according to the ability of transformation of CO2 to methane. The isolated bacteria were called BRS11 strain showed high efficiency in transformation of CO2 to methane.

Combining a robust thermophilic methanogen and packing material with high liquid hold-up to optimize biological methanation in trickle-bed reactors

The hydrogen gas-to-liquid mass transfer is the limiting factor in biological methanation. In trickle-bed reactors, mass transfer can be increased by high flow velocities in the liquid phase, by adding a packing material with high liquid hold-up or by using methanogenic archaea with a high methane productivity.This study developed a polyphasic approach to address all methods at once. Various methanogenic strains and packings were investigated from a microbial and hydrodynamic perspective. Analyzing the ability to produce high-quality methane and to form biofilms, pure cultures of Methanothermobacter performed better than those of the genus Methanothermococcus. Liquid and static hold-up of a packing material and its capability to facilitate attachment was not attributable to a single property. Consequently, it is recommended to carefully match organism and packing for optimized performance of trickle-bed reactors. The ideal combination for the ORBIT-system was identified as Methanothermobacter thermoautotrophicus IM5 and DuraTop®.

Early response of methanogenic archaea to H2 as evaluated by metagenomics and metatranscriptomics

BackgroundThe molecular machinery of the complex microbiological cell factory of biomethane production is not fully understood. One of the process control elements is the regulatory role of hydrogen (H2). Reduction of carbon dioxide (CO2) by H2 is rate limiting factor in methanogenesis, but the community intends to keep H2 concentration low in order to maintain the redox balance of the overall system. H2 metabolism in methanogens becomes increasingly important in the Power-to-Gas renewable energy conversion and storage technologies.ResultsThe early response of the mixed mesophilic microbial community to H2 gas injection was investigated with the goal of uncovering the first responses of the microbial community in the CH4 formation and CO2 mitigation Power-to-Gas process. The overall microbial composition changes, following a 10 min excessive bubbling of H2 through the reactor, was investigated via metagenome and metatranscriptome sequencing. The overall composition and taxonomic abundance of the biogas producing anaerobic community did not change appreciably 2 hours after the H2 treatment, indicating that this time period was too short to display differences in the proliferation of the members of the microbial community. There was, however, a substantial increase in the expression of genes related to hydrogenotrophic methanogenesis of certain groups of Archaea. As an early response to H2 exposure the activity of the hydrogenotrophic methanogenesis in the genus Methanoculleus was upregulated but the hydrogenotrophic pathway in genus Methanosarcina was downregulated. The RT-qPCR data corroborated the metatranscriptomicResultsH2 injection also altered the metabolism of a number of microbes belonging in the kingdom Bacteria. Many Bacteria possess the enzyme sets for the Wood-Ljungdahl pathway. These and the homoacetogens are partners for syntrophic community interactions between the distinct kingdoms of Archaea and Bacteria.ConclusionsExternal H2 regulates the functional activity of certain Bacteria and Archaea. The syntrophic cross-kingdom interactions in H2 metabolism are important for the efficient operation of the Power-to-Gas process. Therefore, mixed communities are recommended for the large scale Power-to-Gas process rather than single hydrogenotrophic methanogen strains. Fast and reproducible response from the microbial community can be exploited in turn-off and turn-on of the Power-to-Gas microbial cell factories.

Investigating the production of coenzyme F 430 variants in methanogenic archaea

Methanogenesis is the biological production of methane and is utilized by methanogenic archaea (methanogens) as a form of anaerobic respiration to generate energy. Methanogens are found in virtually any anaerobic environment and are responsible for over 70% of total atmospheric methane, a greenhouse gas 84 times more potent than carbon dioxide over a twenty-year period. Due to the abundance of methane and its powerful heat-trapping capability, it is among the most significant greenhouse gases. In addition to methane's importance as a greenhouse gas, it is a valuable and clean energy source that emits 50% less carbon dioxide than coal combustion. An attractive possibility for further exploiting the chemical energy stored in methane is to convert it to more useable liquid fuels and other value-added chemicals. This could be accomplished by producing a methanogenic strain capable of reversing methanogenesis and converting methane to methanol. Before this can be realized, however, the chemistry of methanogenesis must be more fully understood. The final, rate-determining, methane-forming step of methanogenesis is catalyzed by methyl-coenzyme M reductase (MCR) and its prosthetic group, cofactor F430, a unique nickel-containing tetrapyrrole that is the essential catalytic component of MCR. Recently, multiple F430 variants have been discovered in several methanogenic species, including the two model methanogens Methanococcus maripaludis and Methanosarcina acetivorans. Our research suggests that one of these variants, mercaptopropionate-F430, (F430-3) is produced by M. maripaludis almost exclusively in stationary phase of growth, suggesting that nutrient deprivation induces the production of this variant. We hypothesize that hydrogen deprivation is involved in inducing this expression, but future experiments will be conducted to confirm this. We further have implicated a likely enzyme involved in the first step of F430-3 biosynthesis, the insertion of a sulfur atom. This research sets the stage for further investigation into how these two variants modulate MCR catalysis.

Hydrogenotrophic methanogen strain of Methanospirillum from anaerobic digester fed with agro-industrial waste

A hydrogenotrophic, mesophilic methanogen designated as strain T53BJ was isolated from anaerobic digester continuously fed with agro-industrial waste. Cells were stained Gram negative, spiral shaped, motile and found resistant to cell lysis by SDS and hypotonic solution. Growth occurred with optimum (i) temperature of 30 °C (20–40 °C) (ii) pH of 7.0 (6.5–8.5), in the presence of 0.0–0.2 M NaCl with a doubling time of 73.43 h and utilized only hydrogen and carbon dioxide (H2:CO2; 4:1) as a sole source of carbon and energy. The phenetic and phylogenetic analysis based on 16S rRNA and mcrA gene sequences revealed close affiliation of T53BJ strain to the genus Methanospirillum spp. This is the first report about isolation of hydrogenotrophic Methanospirillum spp. from anaerobic digester fed with fruit waste, press mud and neem seed cake, suggesting its potential use for bioaugmentation of anaerobic reactors or upgrading biogas/ syngas to methane.

Methanohalophilus profundi sp. nov., a methylotrophic halophilic piezophilic methanogen isolated from a deep hypersaline anoxic basin

A novel anaerobic methylotrophic halophilic methanogen strain SLHTYROT was isolated from a deep hypersaline anoxic basin called “Tyro” located in the Eastern Mediterranean Sea. Cells of SLHTYROT were motile cocci. The strain SLHTYROT grew between 12 and 37 °C (optimum 30 °C), at pH between 6.5 and 8.2 (optimum pH 7.5) and salinity from 45 to 240 g L−1 NaCl (optimum 135 g L−1). Strain SLHTYROT was methylotrophic methanogen able to use methylated compounds (trimethylamine, dimethylamine, monomethylamine and methanol). Strain SLHTYROT was able to grow at in situ hydrostatic pressure and temperature conditions (35 MPa, 14 °C). Phylogenetic analysis based on 16S rRNA gene and mcrA gene sequences indicated that strain SLHTYROT was affiliated to genus Methanohalophilus within the order Methanosarcinales. It shared >99.16% of the 16S rRNA gene sequence similarity with strains of other Methanohalophilus species. Based on ANIb, AAI and dDDH measurements, and the physiological properties of the novel isolate, we propose that strain SLHTYROT should be classified as a representative of a novel species, for which the name Methanohalophilus profundi sp. nov. is proposed; the type strain is SLHTYROT (=DSM 108854 = JCM 32768 = UBOCC-M-3308).

Development of a simultaneous bioreactor system for characterization of gas production kinetics of methanogenic archaea at high pressure.

Cultivation of methanogens under high pressure offers a great opportunity in biotechnological processes, one of which is the improvement of the gas‐liquid transfer of substrate gases into the medium broth. This article describes a newly developed simultaneous bioreactor system consisting of four identical cultivation vessels suitable for investigation of microbial activity at pressures up to 50 bar and temperatures up to 145°C. Initial pressure studies at 10 and 50 bar of the autotrophic and hydrogenotrophic methanogens Methanothermobacter marburgensis, Methanobacterium palustre, and Methanobacterium thermaggregans were performed to evaluate the reproducibility of the system as well as to test the productivity of these strains. The strains were compared with respect to gas conversion (%), methane evolution rate (MER) (mmol L‐1 h−1), turnover rate (h−1), and maximum conversion rate (k min) (bar h−1). A pressure drop that can be explained by the reaction stoichiometry showed that all tested strains were active under pressurized conditions. Our study sheds light on the production kinetics of methanogenic strains under high‐pressure conditions. In addition, the simultaneous bioreactor system is a suitable first step screening system for analyzing the substrate uptake and/or production kinetics of gas conversion and/or gas production processes for barophilic or barotolerant microbes.

Response of Methanogenic Archaea from Siberian Permafrost and Non-permafrost Environments to Simulated Mars-like Desiccation and the Presence of Perchlorate.

Numerous preflight investigations were necessary prior to the exposure experiment BIOMEX on the International Space Station to test the basic potential of selected microorganisms to resist or even to be active under Mars-like conditions. In this study, methanogenic archaea, which are anaerobic chemolithotrophic microorganisms whose lifestyle would allow metabolism under the conditions on early and recent Mars, were analyzed. Some strains from Siberian permafrost environments have shown a particular resistance. In this investigation, we analyzed the response of three permafrost strains (Methanosarcina soligelidi SMA-21, Candidatus Methanosarcina SMA-17, Candidatus Methanobacterium SMA-27) and two related strains from non-permafrost environments (Methanosarcina mazei, Methanosarcina barkeri) to desiccation conditions (-80°C for 315 days, martian regolith analog simulants S-MRS and P-MRS, a 128-day period of simulated Mars-like atmosphere). Exposure of the different methanogenic strains to increasing concentrations of magnesium perchlorate allowed for the study of their metabolic shutdown in a Mars-relevant perchlorate environment. Survival and metabolic recovery were analyzed by quantitative PCR, gas chromatography, and a new DNA-extraction method from viable cells embedded in S-MRS and P-MRS. All strains survived the two Mars-like desiccating scenarios and recovered to different extents. The permafrost strain SMA-27 showed an increased methanogenic activity by at least 10-fold after deep-freezing conditions. The methanogenic rates of all strains did not decrease significantly after 128 days S-MRS exposure, except for SMA-27, which decreased 10-fold. The activity of strains SMA-17 and SMA-27 decreased after 16 and 60 days P-MRS exposure. Non-permafrost strains showed constant survival and methane production when exposed to both desiccating scenarios. All strains showed unaltered methane production when exposed to the perchlorate concentration reported at the Phoenix landing site (2.4 mM) or even higher concentrations. We conclude that methanogens from (non-)permafrost environments are suitable candidates for potential life in the martian subsurface and therefore are worthy of study after space exposure experiments that approach Mars-like surface conditions.

Inhibition of Rumen Methanogens by a Novel Archaeal Lytic Enzyme Displayed on Tailored Bionanoparticles.

Methane is a potent greenhouse gas, 25 times more efficient at trapping heat than carbon dioxide. Ruminant methane emissions contribute almost 30% to anthropogenic sources of global atmospheric methane levels and a reduction in methane emissions would significantly contribute to slowing global temperature rises. Here we demonstrate the use of a lytic enyzme, PeiR, from a methanogen virus that infects Methanobrevibacter ruminantium M1 as an effective agent inhibiting a range of rumen methanogen strains in pure culture. We determined the substrate specificity of soluble PeiR and demonstrated that the enzyme is capable of hydrolysing the pseudomurein cell walls of methanogens. Subsequently, peiR was fused to the polyhydroxyalkanoate (PHA) synthase gene phaC and displayed on the surface of PHA bionanoparticles (BNPs) expressed in Eschericia coli via one-step biosynthesis. These tailored BNPs were capable of lysing not only the original methanogen host strain, but a wide range of other rumen methanogen strains in vitro. Methane production was reduced by up to 97% for 5 days post-inoculation in the in vitro assay. We propose that tailored BNPs carrying anti-methanogen enzymes represent a new class of methane inhibitors. Tailored BNPs can be rapidly developed and may be able to modulate the methanogen community in vivo with the aim to lower ruminant methane emissions without impacting animal productivity.

Stimulatory Effect of Magnetite Nanoparticles on a Highly Enriched Butyrate-Oxidizing Consortium.

Syntrophic oxidation of butyrate is catabolized by a few bacteria specialists in the presence of methanogens. In the present study, a highly enriched butyrate-oxidizing consortium was obtained from a wetland sediment in Tibetan Plateau. During continuous transfers of the enrichment, the addition of magnetite nanoparticles (nanoFe3O4) consistently enhanced butyrate oxidation and CH4 production. Molecular analysis revealed that all bacterial sequences from the consortium belonged to Syntrophomonas with the closest relative of Syntrophomonas wolfei and 96% of the archaeal sequences were related to Methanobacteria with the remaining sequences to Methanocella. Addition of graphite and carbon nanotubes for a replacement of nanoFe3O4 caused the similar stimulatory effect. Silica coating of nanoFe3O4 surface, however, completely eliminated the stimulatory effect. The control experiment with axenic cultivation of a Syntrophomonas strain and two methanogen strains showed no effect by nanoFe3O4. Together, the results in the present study support that syntrophic oxidation of butyrate is likely facilitated by direct interspecies electron transfer in the presence of conductive nanomaterials.

Physiology and methane productivity of Methanobacterium thermaggregans

Accumulation of carbon dioxide (CO2), associated with global temperature rise, and drastically decreasing fossil fuels necessitate the development of improved renewable and sustainable energy production processes. A possible route for CO2 recycling is to employ autotrophic and hydrogenotrophic methanogens for CO2-based biological methane (CH4) production (CO2-BMP). In this study, the physiology and productivity of Methanobacterium thermaggregans was investigated in fed-batch cultivation mode. It is shown that M. thermaggregans can be reproducibly adapted to high agitation speeds for an improved CH4 productivity. Moreover, inoculum size, sulfide feeding, pH, and temperature were optimized. Optimization of growth and CH4 productivity revealed that M. thermaggregans is a slightly alkaliphilic and thermophilic methanogen. Hitherto, it was only possible to grow seven autotrophic, hydrogenotrophic methanogenic strains in fed-batch cultivation mode. Here, we show that after a series of optimization and growth improvement attempts another methanogen, M. thermaggregas could be adapted to be grown in fed-batch cultivation mode to cell densities of up to 1.56 g L−1. Moreover, the CH4 evolution rate (MER) of M. thermaggregans was compared to Methanothermobacter marburgensis, the CO2-BMP model organism. Under optimized cultivation conditions, a maximum MER of 96.1 ± 10.9 mmol L−1 h−1 was obtained with M. thermaggregans—97% of the maximum MER that was obtained utilizing M. marburgensis in a reference experiment. Therefore, M. thermaggregans can be regarded as a CH4 cell factory highly suited to be applicable for CO2-BMP.

Effect of different ammonia sources on aceticlastic and hydrogenotrophic methanogens

Ammonium chloride (NH4Cl) was usually used as a model ammonia source to simulate ammonia inhibition during anaerobic digestion (AD) of nitrogen-rich feedstocks. However, ammonia in AD originates mainly from degradation of proteins, urea and nucleic acids, which is distinct from NH4Cl. Thus, in this study, the inhibitory effect of a “natural” ammonia source (urea) and NH4Cl, on four pure methanogenic strains (aceticlastic: Methanosarcina thermophila, Methanosarcina barkeri; hydrogenotrophic: Methanoculleus bourgensis, Methanoculleus thermophilus), was assessed under mesophilic (37 °C) and thermophilic (55 °C) conditions. The results showed that urea hydrolysis increased pH significantly to unsuitable levels for methanogenic growth, while NH4Cl had a negligible effect on pH. After adjusting initial pH to 7 and 8, urea was significantly stronger inhibitor with longer lag phases to methanogenesis compared to NH4Cl. Overall, urea seems to be more toxic on both aceticlastic and hydrogenotrophic methanogens compared to NH4Cl under the same total and free ammonia levels.

Influence of H2S-producing chemical species in culture medium and energy source starvation on carbon steel corrosion caused by methanogens

Investigations in microbiological-influenced corrosion in recent years have suggested a positive correlation in steel corrosion with methanogens. However, many cases reported in the literature were performed in medium containing Na2S·9H2O or l-cysteine, from which the methanogens can produce H2S that in itself is corrosive. Here it is demonstrated that if all sources of H2S are removed, the methanogenic strain Methanosarcina barkeri only cause accelerated corrosion when deprived of traditional energy sources for methanogenesis, such as methanol and H2. Possible mechanisms for this phenomenon of starvation conditions triggering accelerated corrosion are discussed.

Metagenomic and Metatranscriptomic Analysis of an Electromethanogenic Microbial Community

Researchers have described the mechanisms of extracellular electron uptake in model electrogens like Shewanella oneidensis MR-11 and Geobacter sulfurreducens2 as well as providing evidence for direct electron uptake for some methanogenic strains in BESs3. However, practical applications of BESs will require the use of mixed microbial populations to ensure performance stability by taking advantage of microbial adaptation and symbioses that can reduce the impact of environmental or operational perturbations. However, little is known about the taxonomic composition of mixed microbial biofilms that successfully drive electromethanogenesis. Even less is known about the functional association of specific genes and pathways expressed by microbial community members that enable cooperation/competition in an electromethanogenic system. Here we utilized a novel stimulus-induced metatranscriptomic approach in combination with metagenomics to identify the microbial taxa in an electromethanogenic biofilm and quantify the dynamic responses of key genes associated with electron uptake, hydrogen production/utilization and carbon dioxide fixation. Two dual-compartment bioelectrochemical systems (BES1 and BES2) were inoculated with rice paddy soil, a minimal media without additional soluble carbon sources or chemical mediators, and a 20% CO2 headspace (balance N2). The systems were operated as described in Bretschger et al.4 using a subpassage technique to accelerate the enrichment of highly active electromethanogenic communities. The stimulus-induced metatranscriptomic experiments and metagenomic analyses were executed according to methods described in Ishii et al.5 , 6. Both systems were exposed to an open circuit condition for 45 minutes and biofilms were sampled before and after the operational change (Fig. 1a, main). At the time of sampling both systems were consuming electricity and producing methane (Fig. 1a, inset). However, BES2 was consuming more electrons per unit biomass than BES2, even though both systems had roughly equivalent methane production activity. The results from the metagenomic analyses show that the same strains of methanogens, sulfate reducers and fermenters were present in BES1 and BES2; however, they were present in different relative abundances, which may explain the performance differences (Fig. 1b and c). Further, the stimuli applied to both reactors induced different functional responses from the respective communities, which also indicates that the relative abundance of species impacts how they functionally respond in BESs. Future work will address the specific interactions that correlate with these performance differences. These data yield new perspectives on the functional and taxonomic dynamics of electromethanogenic microbial communities and how they may be controlled in BESs. 1 Ross, D. E., Flynn, J. M., Baron, D. B., Gralnick, J. A. & Bond, D. R. Towards electrosynthesis in Shewanella: energetics of reversing the Mtr pathway for reductive metabolism. PloS one 6, e16649 (2011). 2 Gregory, K. B., Bond, D. R. & Lovley, D. R. Graphite electrodes as electron donors for anaerobic respiration. Environmental Microbiology 6, 596-604 (2004). 3 Lohner, S. T., Deutzmann, J. S., Logan, B. E., Leigh, J. & Spormann, A. M. Hydrogenase-independent uptake and metabolism of electrons by the archaeon Methanococcus maripaludis. The ISME journal 8, 1673-1681 (2014). 4 Bretschger, O. et al. Functional and taxonomic dynamics of an electricity-consuming methane-producing microbial community. Bioresource technology 195, 254-264 (2015). 5 Ishii, S. i. et al. A novel metatranscriptomic approach to identify gene expression dynamics during extracellular electron transfer. Nature Communications, doi:doi:10.1038/ncomms2615 (2013). 6 Ishii, S. i. et al. Microbial metabolic networks in a complex electrogenic biofilm recovered from a stimulus-induced metatranscriptomics approach. Scientific reports 5 (2015). Figure 1