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Methanogens are methane-producing, hydrogen-oxidizing (i.e. hydrogenotrophic) archaea. Numerous studies have associated methanogens with obesity, but these results have been inconsistent. One link to metabolism may be methanogens’ hydrogen-oxidizing ability, thus reducing hydrogen partial pressure and thermodynamically enhancing fermentation of sugars to short-chain fatty acids (SCFAs) that the host can absorb. Because research linking methanogenesis to human metabolism is limited, our goal with this exploratory analysis was to investigate relationships between methanogens and other hydrogenotrophs, along with the association of methanogens with human metabolizable energy (ME). Using results from a randomized crossover feeding study including a western diet and a high-fiber diet, well-characterized human participants, and continuous methane measurements, we analyzed hydrogenotroph abundance and activity, fecal and serum SCFAs, and host ME between high and low methane producers. We detected methanogens in about one-half of participants. We found no evidence that methanogens’ consumption of hydrogen to produce methane affected other hydrogenotrophs. High methane producers had greater serum propionate and greater gene and transcript abundance of a key enzyme of the hydrogen-consuming, propionate-producing succinate pathway. High methane producers also had greater ME than low producers on the high-fiber diet. A network analysis revealed positive relationships between the methane-production rate and bacteria capable of degrading fiber and fermenting fiber-degradation products, thus forming a trophic chain to extract additional energy from undigested substrates. Our results show that methanogenesis in a microbial consortium was linked to host ME through enhanced microbial production, and subsequent host absorption, of SCFAs.

This study revealed that microbes enriched from groundwater in a 380-m deep borehole within the Siljan meteorite impact crater in Sweden were capable of producing methane, a key greenhouse gas. This is especially significant because it is the first proof of active methanogens in an impact crater and showing a specific pathway of methane production—methylotrophic methanogenesis—is present in the deep terrestrial subsurface, an environment that is typically hard to study. These findings shed light on life in extreme conditions on Earth and show that meteorite craters can be biological hotspots, rich with ancient life processes.

Background Methane-utilizing bacteria (methanotrophs) are capable of growth on methane and are attractive systems for bio-catalysis. However, the application of natural methanotrophic strains to large-scale production of value-added chemicals/biofuels requires a number of physiological and genetic alterations. An accurate metabolic model coupled with flux balance analysis can provide a solid interpretative framework for experimental data analyses and integration. Results A stoichiometric flux balance model of Methylomicrobium buryatense strain 5G(B1) was constructed and used for evaluating metabolic engineering strategies for biofuels and chemical production with a methanotrophic bacterium as the catalytic platform. The initial metabolic reconstruction was based on whole-genome predictions. Each metabolic step was manually verified, gapfilled, and modified in accordance with genome-wide expression data. The final model incorporates a total of 841 reactions (in 167 metabolic pathways). Of these, up to 400 reactions were recruited to produce 118 intracellular metabolites. The flux balance simulations suggest that only the transfer of electrons from methanol oxidation to methane oxidation steps can support measured growth and methane/oxygen consumption parameters, while the scenario employing NADH as a possible source of electrons for particulate methane monooxygenase cannot. Direct coupling between methane oxidation and methanol oxidation accounts for most of the membrane-associated methane monooxygenase activity. However the best fit to experimental results is achieved only after assuming that the efficiency of direct coupling depends on growth conditions and additional NADH input (about 0.1–0.2 mol of incremental NADH per one mol of methane oxidized). The additional input is proposed to cover loss of electrons through inefficiency and to sustain methane oxidation at perturbations or support uphill electron transfer. Finally, the model was used for testing the carbon conversion efficiency of different pathways for C 1 -utilization, including different variants of the ribulose monophosphate pathway and the serine cycle. Conclusion We demonstrate that the metabolic model can provide an effective tool for predicting metabolic parameters for different nutrients and genetic perturbations, and as such, should be valuable for metabolic engineering of the central metabolism of M. buryatense strains.

Aerobic gammaproteobacterial methanotrophs can survive and grow in anoxic lakes, but mechanisms that provide them with oxygen to support methane oxidation remain uncharacterized. Methylomonas denitrificans FJG1 encodes 10 copies of bacteriohemerthyrin ( bhr ), of which seven are expressed at the mRNA level under low oxygen conditions. Comparing the 10 bhr homologs from M. denitrificans FJG1 with those from other methanotrophs and bacterial genomes shows that two are specific to methanotrophs. Gene neighborhoods surrounding conserved bhr genes in methanotrophs suggest a range of potential functions, including oxygen respiration, oxygen sensing, chemotaxis, and nitrate reduction. The results from this study illuminate a previously undescribed diversity of structures and potential functions of bhr homologs in M. denitrificans FJG1 and related methanotrophic bacteria. The results pinpoint a methanotroph-specific homolog, bhr -00, that is likely responsible for oxygen binding and delivery to methane monooxygenase enzymes to promote methane oxidation in low oxygen ecosystems.

The anaerobic digestion efficiency and methane production of straw was limited by its complex composition and structure. In this study, rice straw (RS), cellulose, and hemicellulose were used as raw materials to study biogas production performance and changes in the volatile fatty acids (VFAs). Further, microbial communities and genetic functions were analyzed separately for each material. The biogas production potential of RS, cellulose, and hemicellulose was different, with cumulative biogas production of 283.75, 412.50, and 620.64 mL/(g·VS), respectively. The methane content of the biogas produced from cellulose and hemicellulose was approximately 10% higher than that produced from RS after the methane content stabilized. The accumulation of VFAs occurred in the early stage of anaerobic digestion in all materials, and the cumulative amount of VFAs in both cellulose and hemicellulose was relatively higher than that in RS, and the accumulation time was 12 and 14 days longer, respectively. When anaerobic digestion progressed to a stable stage, Clostridium was the dominant bacterial genus in all three anaerobic digestion systems, and the abundance of Ruminofilibacter was higher during anaerobic digestion of RS. Genetically, anaerobic digestion of all raw materials proceeded mainly via aceticlastic methanogenesis, with similar functional components. The different performance of anaerobic digestion of RS, cellulose, and hemicellulose mainly comes from the difference of composition of raw materials. Increasing the accessibility of cellulose and hemicellulose in RS feedstock by pretreatment is an effective way to improve the efficiency of anaerobic digestion. Since the similar microbial community structure will be acclimated during anaerobic digestion, there is no need to adjust the initial inoculum when the accessibility of cellulose and hemicellulose changes.

Recent work has demonstrated that among irritable bowel syndrome (IBS) subjects, methane on lactulose breath test (LBT) is nearly universally associated with constipation predominance. This work has been based on subjective constipation outcomes. In this study, methane is compared to constipation in another population of IBS subjects with constipation being determined both subjectively and objectively. A nested study was conducted in subjects enrolled in a double-blind randomized placebo-controlled study. After consent, subjects were asked to complete a stool diary for 7 days. This included logging of all bowel movements that week as well as documenting the stool consistency for each during the same period using the Bristol Stool Score. After 7 days, subjects were asked to rate their symptoms on a visual analogue scale (VAS) score (0-100 mm) for diarrhea and constipation. They then had an LBT to evaluate both methane and hydrogen profiles over 180 min. Subjects with methane were compared to those without methane for Bristol Stool Score, stool frequency, as well as VAS scores for diarrhea and constipation. The degree of constipation was then compared to the quantity of methane production on LBT based on area under the curve. Among 87 subjects, 20 (23.8%) produced methane. IBS subjects with methane had a mean constipation severity of 66.1 +/- 36.7 compared to 36.2 +/- 30.8 for nonmethane producers (P < 0.001). The opposite was noted for diarrhea (P < 0.01). On LBT, the quantity of methane seen on breath test was directly proportional to the degree of constipation reported (r = 0.60, P < 0.01). In addition, greater methane production correlated with a lower stool frequency (r =-0.70, P < 0.001) and Bristol Stool Score (r =-0.58, P < 0.01). Methane on LBT is associated with constipation both subjectively and objectively. The degree of methane production on breath test appears related to the degree of constipation.

The objective of this study was to investigate the effect of microencapsulated bioactive compounds from lemongrass mixed dragon fruit peel pellet (MiEn-LEDRAGON) supplementation on fermentation characteristics, nutrient degradability, methane production, and the microbial diversity using in vitro gas production technique. The study was carried out using a completely randomized design (CRD) with five levels of MiEn-LEDRAGON supplementation at 0, 1, 2, 3, and 4% of the total dry matter (DM) substrate. Supplementation of MiEn-LEDRAGON in the diet at levels of 3 or 4% DM resulted in increased (p < 0.05) cumulative gas production at 96 hours (h) of incubation time, reaching up to 84.842 ml/ 0.5 g DM. Furthermore, supplementation with 3% MiEn-LEDRAGON resulted in higher in vitro nutrient degradability and ammonia–nitrogen concentration at 24 h of the incubation time when compared to the control group (without supplementation) by 5.401% and 11.268%, respectively (p < 0.05). Additionally, supplementation with MiEn-LEDRAGON in the diet led to an increase in the population of Fibrobacter succinogenes at 24 h and Butyrivibrio fibrisolvens at 12 h, while decreasing the population of Ruminococcus albus , Ruminococcus flavefaciens , and Methanobacteriales (p < 0.05). Moreover, supplementation of MiEn-LEDRAGON in the diet at levels of 2 to 4% DM resulted in a higher total volatile fatty acids (VFA) at 24 h, reaching up to 73.021 mmol/L (p < 0.05). Additionally, there was an increased proportion of propionic acid (C3) and butyric acid (C4) at 12 h (p < 0.05). Simultaneously, there was a decrease in the proportion of acetic acid (C2) and the ratio of acetic acid to propionic acid (C2:C3), along with a reduction of methane (CH 4 ) production by 11.694% when comparing to the 0% and 3% MiEn-LEDRAGON supplementation (p < 0.05). In conclusion, this study suggests that supplementing MiEn-LEDRAGON at 3% of total DM substrate could be used as a feed additive rich in phytonutrients for ruminants.

The obstacle to optimal utilization of biogas technology is poor understanding of biogas microbiomes diversities over a wide geographical coverage. We performed random shotgun sequencing on twelve environmental samples. Randomized complete block design was utilized to assign the twelve treatments to four blocks, within eastern and central regions of Kenya. We obtained 42 million paired-end reads that were annotated against sixteen reference databases using two ENVO ontologies, prior to β-diversity studies. We identified 37 phyla, 65 classes and 132 orders. Bacteria dominated and comprised 28 phyla, 42 classes and 92 orders, conveying substrate’s versatility in the treatments. Though, Fungi and Archaea comprised 5 phyla, the Fungi were richer; suggesting the importance of hydrolysis and fermentation in biogas production. High β-diversity within the taxa was largely linked to communities’ metabolic capabilities. Clostridiales and Bacteroidales , the most prevalent guilds, metabolize organic macromolecules. The identified Cytophagales , Alteromonadales , Flavobacteriales , Fusobacteriales , Deferribacterales , Elusimicrobiales , Chlamydiales , Synergistales to mention but few, also catabolize macromolecules into smaller substrates to conserve energy. Furthermore, δ-Proteobacteria , Gloeobacteria and Clostridia affiliates syntrophically regulate P H2 and reduce metal to provide reducing equivalents. Methanomicrobiales and other Methanomicrobia species were the most prevalence Archaea , converting formate, CO 2(g) , acetate and methylated substrates into CH 4(g) . Thermococci , Thermoplasmata and Thermoprotei were among the sulfur and other metal reducing Archaea that contributed to redox balancing and other metabolism within treatments. Eukaryotes, mainly fungi were the least abundant guild, comprising largely Ascomycota and Basidiomycota species. Chytridiomycetes , Blastocladiomycetes and Mortierellomycetes were among the rare species, suggesting their metabolic and substrates limitations. Generally, we observed that environmental and treatment perturbations influenced communities’ abundance, β-diversity and reactor performance largely through stochastic effect. Understanding diversity of biogas microbiomes over wide environmental variables and its’ productivity provided insights into better management strategies that ameliorate biochemical limitations to effective biogas production.

Ruminant livestock are major contributors to global methane emissions, largely through microbial fermentation in the rumen. Understanding how microbial communities vary between high- and low-methane-emitting animals is critical for identifying mitigation strategies. This study leverages a genome-centric approach to link microbial metabolic traits to methane output in cattle. By reconstructing and functionally characterizing hundreds of microbial genomes, we observe that a low-methane-emission rumen harbors well-balanced, “streamlined” microbial communities characterized by high metabolic capacity and minimal metabolic overlap across populations (low functional redundancy). Our results demonstrate the utility of genome-level functional profiling in uncovering microbial community traits tied to climate-relevant phenotypes.

The aim of this study is to evaluate the effect of rice, mung bean, and wheat noodle ingestion on intestinal gas production and postprandial gastrointestinal (GI) symptoms in non-constipation irritable bowel syndrome (IBS) patients. Methods: Twenty patients (13 F, 46 ± 11 y) underwent 8 h breath test studies and GI symptom evaluations after standard rice, wheat, or mung bean noodle meals at 8:00 a.m. in a randomized crossover study with a 1-week washout period. The same meal was ingested at 12:00 p.m. Results: The H2 and CH4 concentration in the breath samples were similar at baseline (rice:wheat:mung bean, H2 = 3.6 ± 0.5:4.1 ± 0.5:4.0 ± 0.7 ppm, CH4 = 1.3 ± 0.3:2.1 ± 0.4:1.9 ± 0.4 ppm, p > 0.05). Beginning at the fifth hour after breakfast, H2 and CH4 concentrations significantly increased after wheat compared to rice and mung bean (8 h AUC H2 = 4120 ± 2622:2267 ± 1780:2356 ± 1722, AUC CH4 = 1617 ± 1127:946 ± 664:943 ± 584 ppm-min, respectively) (p < 0.05). Bloating and satiety scores significantly increased after wheat compared to rice (p < 0.05), and increased but did not reach statistical significance compared to mung bean (p > 0.05). A higher bloating score after wheat compared to rice and mung bean was observed clearly after lunch but not after breakfast. Conclusion: Wheat ingestion produced more intestinal gas and more bloating and satiety scores compared to rice and mung bean, especially after lunch. This provides insight into the role of intestinal gas in the development of bloating symptoms in IBS.