Showing papers on "Methanogen published in 2023"

Improving Methane Production from Waste Activated Sludge Assisted by Fe(II)-Activated Peroxydisulfate Pretreatment via Anaerobic Digestion: Role of Interspecific Syntrophism Mediated by Sulfate-Reducing Bacteria

Abstract: Sulfate radical generated via peroxydisulfate (PDS) activation has been extensively applied to energy recovery from waste activated sludge (WAS) during anaerobic digestion (AD), while the residual sulfate is still a limitation for its further application. In this study, a novel coupling strategy of Fe(II)-activated PDS pretreatment [Fe(II)_PDS] with sulfate-reducing bacteria (SRB) mediated was explored to enhance methane yield from WAS during AD. Results showed that the similar methane yield was obtained in Fe(II)_PDS + SRB (16.6 mL/g VSS) and zero-valent iron (ZVI)_PDS + SRB (16.9 mL/g VSS), which enhanced by 19.9–56.5% than other groups, while the hydrolysis rate constant (0.0065 h–1) in Fe(II)_PDS + SRB was much higher than that observed in ZVI_PDS + SRB (0.0046 h–1). Meanwhile, the concentration of short-chain fatty acids (SCFAs) peaked at 360.9 mg COD/g VSS (5 d) in the Fe(II)_PDS + SRB group, with the acetic acid (HAc) and propionic acid (HPr) accumulative proportion of 73.5%, and the total concentration promoted by 28.5% than that of the ZVI_PDS + SRB group, which provided a more ideal substrate for methanogens. The ultimate utilization efficiency of SCFAs reached 62.4% in the Fe(II)_PDS + SRB group. Moreover, MiSeq sequencing, canonical correspondence analysis, and molecular ecological network analysis revealed the intrinsic interaction of the functional microbial consortia, that is, anaerobic fermentation bacteria, SRB, nitrate-reducing bacterium, and acetotrophic methanogen, with the abundances of 9.52, 2.4, 4.93, and 77.7% in the Fe(II)_PDS + SRB group. Considering the treatment performance and the difficulty of the subsequent disposal, Fe(II) may be the superior activator than ZVI for free radicals (i.e., SO4•– and HO•) generation from PDS and further played the important role for interspecific syntrophism coupling with SRB during AD. Results of this study may provide a promising way for energy recovery from WAS.

Effects of increasing phenyl acid concentrations on the AD process of a multiple-biogas-reactor system

Abstract: Anaerobic digestion (AD) of organic waste materials is an ecological way to produce biogas. However, organic wastes can comprise high amounts of aromatic compounds like phenyl acids (PA) which can cause process impairments. Here, three of six thermophilic, semi-continuously fed biogas reactors were exposed to increasing PA concentrations at two different input speeds (consecutive experiments). Biochemical (gas, volatile fatty acid (VFA) and PA analyses) as well as molecular biological analyses (qPCR and amplicon sequencing) were done to monitor the AD process. Biogas production was completely inhibited at the end of both approaches. An increase in acetate and propionate concentrations were the earliest signs of process impairments. Methanosarcina spp. was the dominant methanogen during biogas production; however, their absolute abundances were low in impaired reactors. Syntrophic VFA oxidation and hydrogenotrophic methanogenesis became relevant in impaired but still biogas producing reactors. The combination of biochemical and metagenomic data and the consideration of input speed using six parallel, lab-scale bioreactors showed that a decrease in biogas production is a time-delayed sign of process impairments and VFA monitoring on-site would be useful to early counteract impeding restrictions. Moreover, this study confirmed that syntrophic VFA oxidation is relevant in stressed AD systems and that further knowledge on these cooperations is pending.

In situ field experiment shows the potential of methanogenic archaea for biomethane production from underground gas storage in natural rock environment

Abstract: Biological methanation occurs naturally in the specific rock environment of some underground gas reservoirs. To use the natural potential of hydrogenotrophic methanogenic archaea in the underground gas reservoirs environment in the future for any type of energy conversion, better knowledge of these systems is required. Most studies investigating the potential for biological methane production from hydrogen and carbon dioxide have been conducted in laboratory-scale systems, making it impossible to evaluate the process under realistic environmental conditions. A unique field experiment of biomethanation in an underground gas reservoir confirmed the feasibility of these facilities for targeted production of biologically produced methane. The experiment followed data previously obtained from long-term experiments carried out in the laboratory, including 300 days lasting operation of reactor and cultivation experiments, which led to repeated isolation of Methanothermobacter sp. This species was the dominant methanogen, which raised from 1% to 43% of all microbial population after 22 days of field experiment, while the complete conversion of hydrogen took place. In addition, the study is supported by metagenomic analysis to gain deep insight into the microbiome of the underground gas reservoir.

Isolation of a methyl-reducing methanogen outside the Euryarchaeota

Abstract: Abstract Methanogenic archaea are main contributors to methane emissions, and thus play a crucial role in carbon cycling and global warming. Until recently, methanogens were confined to the phylum Euryarchaeota, but metagenomic studies revealed the presence of genes encoding the methyl coenzyme M reductase complex in other archaeal clades, thereby opening up the premise that methanogenesis is taxonomically more widespread. Nevertheless, laboratory cultivation of these non-Euryarchaeal methanogens was missing to allow the study of their physiology and to corroborate their potential methanogenic capability. Here we describe a thermophilic co-culture from an oil field, containing a single archaeon (strain LWZ-6) belonging to the proposed order Candidatus Verstraetearchaeia, together with a H2-producing Acetomicrobium sp. CY-2. Strain LWZ-6, for which we propose the name Verstraetearchaeum methanopetracarbonis, is a H2-dependent methylotrophic methanogen. Although previous metagenomic studies speculated on the fermentative potential of Verstraetearchaeial methanogens, strain LWZ-6 does not ferment sugars, peptides, and amino acids. Its energy metabolism is linked to methanogenesis, with methanol and monomethylamine as electron acceptors and H2 as electron donor. Comparative (meta)genome analysis revealed that H2-dependent methylotrophic methanogenesis is a shared trait among Verstraetearchaeia. Our findings corroborate that the diversity of methanogens expands beyond the classical Euryarchaeota and change our current conception of the global carbon cycle.

Cultivation and visualization of a methanogen of the phylum Thermoproteota

Abstract: Abstract Methane is the second most abundant climate-active gas and understanding its sources and sinks is a crucial endeavor in microbiology, biogeochemistry, and climate sciences (1,2). For decades, it was thought that methanogenesis, the ability to conserve energy coupled to methane production, was restricted to a taxonomically and metabolically specialized group of archaea, the Euryarchaeota1. The discovery of marker genes for anaerobic alkane cycling in metagenome-assembled genomes obtained from diverse habitats has led to the hypothesis that archaeal lineages outside the Euryarchaeota are involved in methanogenesis (3-6). Here, we cultured Candidatus Methanosuratincola yellowstonensis, a member of the archaeal phylum Thermoproteota, from a terrestrial hot spring. Growth experiments combined with activity assays, stable isotope tracing, and genomic analyses confirmed that this thermophilic archaeon grows via methyl-reducing hydrogenotrophic methanogenesis. Cryo-electron tomography revealed that Ca. M. yellowstonensis cells are archaellated coccoid cells that form intercellular bridges, providing two to three cells with a continuous cytoplasm and S-layer. The wide environmental distribution of Ca. M. yellowstonensis suggests that they might play important and hitherto overlooked roles in carbon cycling within diverse anoxic habitats.

Improved Quantitative Real-Time PCR Protocol for Detection and Quantification of Methanogenic Archaea in Stool Samples

Abstract: Methanogenic archaea are an important component of the human and animal intestinal microbiota, and yet their presence is rarely reported in publications describing the subject. One of the methods of quantifying the prevalence of methanogens is quantitative real-time PCR (qPCR) of the methanogen-specific mcrA gene, and one of the possible reasons for detection failure is usually a methodology bias. Here, we refined the existing protocol by changing one of the primers and improving the conditions of the qPCR reaction. As a result, at the expense of a slightly lower yet acceptable PCR efficiency, the new assay was characterized by increased specificity and sensitivity and a wider linear detection range of 7 orders of magnitude. The lowest copy number of mcrA quantified at a frequency of 100% was 21 copies per reaction. The other validation parameters tested, such as reproducibility and linearity, also gave satisfactory results. Overall, we were able to minimize the negative impacts of primer dimerization and other cross-reactions on qPCR and increase the number of not only detectable but also quantifiable stool samples—or in this case, chicken droppings.

Assimilatory sulfate reduction in the marine methanogen Methanothermococcus thermolithotrophicus

Abstract: Methanothermococcus thermolithotrophicus is the only known methanogen that grows on sulfate as its sole sulfur source, uniquely uniting methanogenesis and sulfate reduction. Here we use physiological, biochemical and structural analyses to provide a snapshot of the complete sulfate reduction pathway of this methanogenic archaeon. We find that later steps in this pathway are catalysed by atypical enzymes. PAPS (3'-phosphoadenosine 5'-phosphosulfate) released by APS kinase is converted into sulfite and 3'-phosphoadenosine 5'-phosphate (PAP) by a PAPS reductase that is similar to the APS reductases of dissimilatory sulfate reduction. A non-canonical PAP phosphatase then hydrolyses PAP. Finally, the F420-dependent sulfite reductase converts sulfite to sulfide for cellular assimilation. While metagenomic and metatranscriptomic studies suggest that the sulfate reduction pathway is present in several methanogens, the sulfate assimilation pathway in M. thermolithotrophicus is distinct. We propose that this pathway was 'mix-and-matched' through the acquisition of assimilatory and dissimilatory enzymes from other microorganisms and then repurposed to fill a unique metabolic role.

Kinetics for the Methanogen’s Death in the Acidic Environments

Abstract: This study focuses on the inactivation of methanogens under acidic environment that may arise due to overloading of anaerobic reactors. Two types of methanogen-enriched cultures were prepared in the lab-scale reactors using acetate and formate as substrate. Each culture was subsequently incubated in a batch reactor for 6 days under different pH conditions with one of the VFAs of formate, acetate, propionate, butyrate, valerate or phosphate buffer solution. Propidium-monoazide quantitative polymerase chain reaction (PMA-qPCR) analysis and the methane production test revealed that the methanogenic archaea were highly sensitive to the acidic environment. Under the moderate pH of 6.5–7.5, no significant change in cellular decay was observed. However, at pH below 6.5 the decay rate was accelerated leading to archaea’s inactivation. At pH 5.0, the archaeal specific decay rates were elevated as high as 40 times of that at pH 7.0. When the operational pH was the same in the experiments, the cellular decay rate was comparable between the batch test with VFA and that without VFA. These observations strongly suggest that the methanogen decay is caused by low pH rather than the elevated concentrations of VFA compounds (15–40 mM of undissociated VFA) during acidic failure of anaerobic digester.

Bioaugmentation Strategies for Enhancing Methane Production from Shrimp Processing Waste through Anaerobic Digestion

Abstract: Bioaugmentation strategies were tested to improve energetic valorization of shrimp processing waste (SPW) by anaerobic digestion (AD). A fermenting bacteria pool (F210) obtained from coastal lake sediments and two strains of anaerobic fungi (AF), Orpynomyces sp. and Neocallimastix sp., commonly found as components of microbial community of AD plants, were used with the aim of improving the fermentative and hydrolytic phases of AD, respectively. The experiment was carried out by testing single bioaugmentation at an SPW concentration of 6.5 gVS L−1 and combined bioaugmentation at three SPW concentrations (6.5, 9.7 and 13.0 gVS L−1, respectively), in batch mode and mesophilic conditions. Cumulative CH4 productions were higher in the combined bioaugmentation tests and increased in line with SPW concentration. The F210 played a key role in enhancing CH4 production while no effect was attributable to the addition of AFs. The CH4 content (%) in the biogas increased with substrate concentrations, with average values of 67, 70, and 73%, respectively. Microbial community abundance increased in line with the SPW concentration and the acetoclastic Methanosarcina predominated within the methanogen Archaea guild in the combined bioaugmentation test (in all cases > 65%).

Cross-Feedings, Competition, and Positive and Negative Synergies in a Four-Species Synthetic Community for Anaerobic Degradation of Cellulose to Methane

Abstract: A synthetic community was designed using four microbial species that together performed distinct key metabolic processes in the anaerobic degradation of cellulose to methane and CO2. The microorganisms exhibited expected interactions, such as cross-feeding of acetate from a cellulolytic bacterium to an acetoclastic methanogen and competition of H2 between a sulfate reducing bacterium and a hydrogenotrophic methanogen. ABSTRACT Complex interactions exist among microorganisms in a community to carry out ecological processes and adapt to changing environments. Here, we constructed a quad-culture consisting of a cellulolytic bacterium (Ruminiclostridium cellulolyticum), a hydrogenotrophic methanogen (Methanospirillum hungatei), an acetoclastic methanogen (Methanosaeta concilii), and a sulfate-reducing bacterium (Desulfovibrio vulgaris). The four microorganisms in the quad-culture cooperated via cross-feeding to produce methane using cellulose as the only carbon source and electron donor. The community metabolism of the quad-culture was compared with those of the R. cellulolyticum-containing tri-cultures, bi-cultures, and mono-culture. Methane production was higher in the quad-culture than the sum of the increases in the tri-cultures, which was attributed to a positive synergy of four species. In contrast, cellulose degradation by the quad-culture was lower than the additive effects of the tri-cultures which represented a negative synergy. The community metabolism of the quad-culture was compared between a control condition and a treatment condition with sulfate addition using metaproteomics and metabolic profiling. Sulfate addition enhanced sulfate reduction and decreased methane and CO2 productions. The cross-feeding fluxes in the quad-culture in the two conditions were modeled using a community stoichiometric model. Sulfate addition strengthened metabolic handoffs from R. cellulolyticum to M. concilii and D. vulgaris and intensified substrate competition between M. hungatei and D. vulgaris. Overall, this study uncovered emergent properties of higher-order microbial interactions using a four-species synthetic community. IMPORTANCE A synthetic community was designed using four microbial species that together performed distinct key metabolic processes in the anaerobic degradation of cellulose to methane and CO2. The microorganisms exhibited expected interactions, such as cross-feeding of acetate from a cellulolytic bacterium to an acetoclastic methanogen and competition of H2 between a sulfate reducing bacterium and a hydrogenotrophic methanogen. This validated our rational design of the interactions between microorganisms based on their metabolic roles. More interestingly, we also found positive and negative synergies as emergent properties of high-order microbial interactions among three or more microorganisms in cocultures. These microbial interactions can be quantitatively measured by adding and removing specific members. A community stoichiometric model was constructed to represent the fluxes in the community metabolic network. This study paved the way toward a more predictive understanding of the impact of environmental perturbations on microbial interactions sustaining geochemically significant processes in natural systems.

The key regulative parameters in pilot-scale IC reactor for effective incineration landfill leachate treatment: Focus on the process performance and microbial community

Abstract: Anaerobic digestion is a promising sustainable method for treating highly concentrated organic wastewater from the point of energy recovery. In this study, a pilot-scale internal circulation (IC) reactor was constructed to investigate the key regulative parameters that guaranteed the stable and efficient treatment of incineration leachate. The IC reactor was operated for 77 d by feeding real incineration leachate. With an organic load rate (OLR) of 30 kg/ (m3·d) and an influent pH value of 7.5, the reactor achieved its highest organic removal loading rate (ORLR) and biogas yield of 21 kg/ (m3·d) and 6.3 m3/d, respectively. The kinetic analysis confirmed that the two key parameters that significantly correlated (P < 0.05) with the methane yield and Rmax of sludge were OLR and influent pH value. Key enzyme activity of F420 increased 33.2 % when OLR was raised, but decreased by 5.6 % when influent pH was lowered to 6.8, further demonstrating the need for control over these two operational parameters of IC reactor. High-throughput sequencing results indicated that acetotrophic methanogen Methanosaeta had an overwhelming relative abundance of over 47.2 % in the entire community of all sludge samples. Nevertheless, the enrichment of unclassified_Bacteroidales and Methanobacterium strengthened hydrogenotrophic methanogenesis (HM) with step raise of OLR to 30 kg/ (m3·d), then increased the methane production potential and F420 activity of sludge. This study proposed a referable regulation method for the treatment of the actual landfill leachate via IC reactor.

Physiological Responses of Methanosarcina barkeri under Ammonia Stress at the Molecular Level: The Unignorable Lipid Reprogramming.

Abstract: Acetotrophic methanogens' dysfunction in anaerobic digestion under ammonia pressure has been widely concerned. Lipids, the main cytomembrane structural biomolecules, normally play indispensable roles in guaranteeing cell functionality. However, no studies explored the effects of high ammonia on acetotrophic methanogens' lipids. Here, a high-throughput lipidomic interrogation deciphered lipid reprogramming in representative acetoclastic methanogen (Methanosarcina barkeri) upon high ammonia exposure. The results showed that high ammonia conspicuously reduced polyunsaturated lipids and longer-chain lipids, while accumulating lipids with shorter chains and/or more saturation. Also, the correlation network analysis visualized some sphingolipids as the most active participant in lipid-lipid communications, implying that the ammonia-induced enrichment in these sphingolipids triggered other lipid changes. In addition, we discovered the decreased integrity, elevated permeability, depolarization, and diminished fluidity of lipid-supported membranes under ammonia restraint, verifying the noxious ramifications of lipid abnormalities. Additional analysis revealed that high ammonia destabilized the structure of extracellular polymeric substances (EPSs) capable of protecting lipids, e.g., declining α-helix/(β-sheet + random coil) and 3-turn helix ratios. Furthermore, the abiotic impairment of critical EPS bonds, including C-OH, C═O-NH-, and S-S, and the biotic downregulation of functional proteins involved in transcription, translation, and EPS building blocks' supply were unraveled under ammonia stress and implied as the crucial mechanisms for EPS reshaping.

Anaerobic Digestion of Microalga Chlorella protothecoides and Metagenomic Analysis of Reddish-Colored Digestate

Abstract: Microalga Chlorella protothecoides materials were assessed as substrates for anaerobic digestion (AD) aiming at the simultaneous production of biogas/methane and pigments: whole autotrophic (AA) and heterotrophic algae (H); extracted heterotrophic microalgae from lipid production (HExt); and pretreated heterotrophic microalgae through enzymatic (HPEnz), autoclave (HPA), and ultrasound (HPU) processes. AA was more suitable for AD than H, as it was more efficiently converted into methane (279 vs. 180 L CH4/kg VSin). In comparison, the pretreatment of heterotrophic microalgae had a positive effect on AD, with registered methane yield increases from 263 to 290 L CH4/kg VSin (HPU, HPA, HExt). Reddish pigmentation developed in H and HPU units due to the presence of purple non-sulfur bacteria (PNSB). This phenomenon and the changes in microbiota structure during AD were confirmed by metagenomic analysis. At the end of the process, the relative abundance of Clostridiales and Bacillales increased, enhancing the hydrolysis of compounds in acetate. Consistently, Methanosaeta became the comparatively dominant methanogen, meaning that methane was produced through the acetoclastic methanogenesis pathway. The obtained results indicate for AD biorefinery feasibility—regarding the simultaneous production of biogas/methane—a digestate flow and pigments (bacteriochlorophyll a and carotenoids).

Investigation of the Critical Biomass of Acclimated Microbial Communities to High Ammonia Concentrations for a Successful Bioaugmentation of Biogas Anaerobic Reactors with Ammonia Inhibition

Abstract: This study aimed to investigate the role of the bioaugmented critical biomass that should be injected for successful bioaugmentation for addressing ammonia inhibition in anaerobic reactors used for biogas production. Cattle manure was used as a feedstock for anaerobic digestion (AD). A mixed microbial culture was acclimated to high concentrations of ammonia and used as a bioaugmented culture. Different volumes of bioaugmented culture were injected in batch anaerobic reactors under ammonia toxicity levels i.e., 4 g of NH4+-N L−1. The results showed that injecting a volume equal to 65.62% of the total working reactor volume yielded the best methane production. Specifically, this volume of bioaugmented culture resulted in methane production rates of 196.18 mL g−1 Volatile Solids (VS) and 245.88 mL g−1 VS after 30 and 60 days of AD, respectively. These rates were not significantly different from the control reactors (30d: 205.94 mL CH4 g−1 VS and 60d: 230.26 mL CH4 g−1 VS) operating without ammonia toxicity. Analysis of the microbial community using 16S rRNA gene sequencing revealed the dominance of acetoclastic methanogen members from the genus Methanosaeta in all reactors.

Accelerated Methanogenesis for the Conversion of Biomethane from Carbon Dioxide and Biohydrogen at Hyperthermophilic Condition

Abstract: Abstract Methanogenesis is the conversion of carbon dioxide (CO2) to methane (CH4) using microbes. In the context CO2 utilization, methanogenesis process in the utilizing native microbes from a particular reservoir can be a very slow process without any external intervention. To accelerate the conversion rate and methane yield, this study investigates the use of agriculture by-product such as palm oil mill effluent (POME) as substrates as well as potential microbial isolates that can produce biohydrogen at high temperatures. This paper covers the three laboratory assessments of microbes from anaerobic sludge from a local palm oil mill, use of POME to augment the microbial growth, and physicochemical manipulation to identify key parameters that increases CH4 yield and rate: i) biohydrogen production ii) biomethane production, and iii) syntrophic reactions. All experiments are conducted at 70°C which is considered a hyperthermophilic condition for many microbes. Biohydrogen production achieved with highest H2 production of 66.00 (mL/Lmedium). For biomethane production, the highest production rate achieved was 0.0768 CH4 µmol/mL/day which 10,000X higher than 19.6 pmol/mL/day used as a benchmark. Syntrophic reaction with both types of hydrogen-producing and methanogen in the same reactor, and pure H2 and CO2 supplemented externally was able to achieve the highest methane production of 10.095 µmol/mL and 2.524 µmol/ml/day. Methane production rate is 2.5 times faster than without external gasses being introduced. Introduction of external CO2 to the syntrophic reaction is to mimic actual carbon injection and storage in the reservoir. Our paper shows that stimulation of microbes using POME as substrates and H2/CO2 supplementation are important in accelerating the rate of methane production and yield. Future work will focus on optimizing the gas ratio, pH of growth media, and performing syntrophic reaction in porous media to emulate conditions of a reservoir.

Phylogenetically and physiologically diverse methanogenic archaea inhabit the Indian hot spring environments

Abstract: Abstract Mesophilic and thermophilic methanogens belonging to the hydrogenotrophic, methylotrophic, and acetotrophic groups were isolated from Indian hot spring environments using BY and BCYT growth media. Following initial Hinf I based PCR-RFLP screening, 70 methanogens were sequenced to ascertain their identity. These methanogens were phylogenetically and physiologically diverse and represented different taxa distributed across three physiological groups, i.e. hydrogenotrophs (53), methylotrophs (14) and acetotrophs (3). Overall, methanogens representing three families, five genera, and ten species, including two putative novel species, were recognized. The highest number and diversity of methanogens was observed at 40℃, dominated by Methanobacterium (10; 3 species), Methanosarcina (9; 3 species), Methanothermobacter (7; 2 species), Methanomethylovorans (5; 1 species) and Methanoculleus (3; 1 species). Both putative novel methanogen species were isolated at 40℃ and belonged to the genera Methanosarcina and Methanobacterium . At 55℃, limited diversity was observed, and resulted in the isolation of only two genera of methanogens, i.e., Methanothermobacter (28; 2 species) and Methanosarcina (4; 1 species). At 70℃, only members of the genus Methanothermobacter (5; 2 species) were isolated, whereas no methanogen could be cultured at 85℃. Ours is the first study that documents the extensive range of cultivable methanogenic archaea inhabiting hot springs across various geothermal provinces of India.

Microbial hydrogen consumption leads to a significant pH increase under high-saline-conditions– implications for hydrogen storage in salt caverns

Abstract: Abstract Salt caverns have been successfully used for natural gas storage globally since the 1940s and are now under consideration for hydrogen (H 2 ) storage, which is needed in large quantities for the Green Shift. Salt caverns are not sterile, and H 2 is a ubiquitous electron donor for microorganisms. This could entail that the injected H 2 will be microbially consumed, leading to a volumetric loss and potential production of toxic H 2 S. However, the extent and rates of this microbial H 2 consumption under high-saline cavern conditions are not yet understood. To investigate microbial consumption rates, we cultured the halophilic sulphate-reducing bacteria Desulfohalobium retbaense and the halophilic methanogen Methanocalcus halotolerans under different H 2 partial pressures. Both strains consumed H 2 , but consumption rates slowed down significantly over time. The activity loss correlated with a significant pH increase (up to pH 9) in the media due to intense proton- and bicarbonate consumption. In the case of sulphate-reduction, this pH increase led to dissolution of all produced H 2 S in the liquid phase. We compared these observations to an original brine retrieved from a salt cavern located in Northern Germany, which was incubated with 100% H 2 over several months. We again observed a H 2 loss (up to 12%) with a concurrent increase in pH up to 8.5 especially when additional nutrients were added to the brine. Our results clearly show that sulphate-reducing microbes present in salt caverns will consume H 2 , which will be accompanied by a significant pH increase, resulting in reduced activity over time. This potentially self-limiting process of pH increase during sulphate-reduction will be advantageous for H 2 storage in low-buffering environments like salt caverns.

Origin of biogeographically distinct ecotypes during laboratory evolution

Abstract: Resource partitioning within microbial communities is central to their incredible productivity, including over 1 gigaton of annual methane emissions through syntrophic interactions1. Here, we show how isogenic strains of a sulfate reducing bacterium (Desulfovibrio vulgaris, Dv) and a methanogen (Methanococcus maripaludis, Mm) underwent evolutionary diversification over 300-1,000 generations in a purely planktonic environmental2–4 context giving rise to coexisting ecotypes that could partition resources and improve overall stability, cooperativity, and productivity in a simulated subsurface environment. We discovered that mutations in just 15 Dv and 7 Mm genes gave rise to ecotypes within each species that were spatially enriched between sediment and planktonic phases over the course of only a few generations after transferring the evolved populations to a fluidized bed reactor (FBR). While lactate utilization by Dv in the attached community was significantly greater, the resulting H2 was partially consumed by low affinity hydrogenases in Mm within the same attached phase. The unutilized H2 was scavenged by high affinity hydrogenases in the planktonic phase Mm, generating copious amounts of methane and higher ratio of Mm to Dv. Our findings show how a handful of mutations that arise in one environmental context can drive resource partitioning by ecologically differentiated variants in another environmental context, whose interplay synergistically improves productivity of the entire mutualistic community.

Methanobrevibacter boviskoreani JH1T growth on alcohols allows development of a high throughput bioassay to detect methanogen inhibition

Abstract: Rumen methanogenic archaea use by-products of fermentation to carry out methanogenesis for energy generation. A key fermentation by-product is hydrogen (H2), which acts as the source of reducing potential for methane (CH4) formation in hydrogenotrophic methanogens. The in vitro cultivation of hydrogenotrophic rumen methanogens requires pressurised H2 which limits the ability to conduct high-throughput screening experiments with these organisms. The genome of the hydrogenotrophic methanogen Methanobrevibacter boviskoreani JH1T harbors genes encoding an NADP-dependent alcohol dehydrogenase and a F420-dependent NADP reductase, which may facilitate the transfer of reducing potential from ethanol to F420 via NADP. The aim of this study was to explore the anaerobic culturing of JH1T without pressurised H2, using a variety of short chain alcohols. The results demonstrate that in the absence of H2, JHIT can use ethanol, 1-propanol, and 1-butanol but not methanol, as a source of reducing potential for methanogenesis. The ability to use ethanol to drive CH4 formation in JH1T makes it possible to develop a high throughput culture-based bioassay enabling screening of potential anti-methanogen compounds. The development of this resource will help researchers globally to accelerate the search for methane mitigation technologies for ruminant animals. Global emissions pathways that are consistent with the temperature goal of the Paris Agreement, rely on substantial reductions of agricultural greenhouse gasses, particularly from ruminant animals.

Methanogen-electrode/conductive material interactions for methane production from carbon dioxide

Abstract: Methanogen-electrode/conductive material interactions for renewable biogas and biomethane production from carbon dioxide (CO2) are the key component governing the operations of anaerobic digestion (AD) and microbial electrochemical technologies (METs). However, to optimize methanogenic activities in AD and MET, an understanding of interactions between methanogens and conductive materials/electrodes is required. First, the fundamentals of methanogenesis and electromethanogenesis processes in AD and MET and their electron transfer pathways, such as direct electron transfer, indirect electron transfer, and direct interspecies electron transfer, are discussed. Moreover, we critically examine and scrutinize how different conductive materials, types of anodes and biocathodes, and various operating parameters such as organic loading rates, the food-to-microorganisms ratio, temperatures, mixing, applied energy levels, pH, reactor configurations, inoculum sources, and microbial communities can be engineered to optimize methanogenesis and electromethanogenesis in AD and MET. This chapter provides an overview of different fundamental and applied aspects of interactions between methanogens and conductive materials/electrodes in AD and METs in terms of CO2 use and methane recovery.