Differences down-under: alcohol-fueled methanogenesis by archaea present in Australian macropodids

Comparative assessment of emulsifiers for in vitro ruminal gas production and fermentation measurements: Tween 80 is a suitable emulsifier

Emulsifiers are essential for achieving a homogenous distribution of lipophilic supplements in in vitro rumen fluid incubations. Since emulsifiers can alter rumen fermentation, it is crucial to select one that minimally impacts fermentation parameters to reduce potential biases. This study aimed to evaluate seven emulsifiers' impact on in vitro ruminal fermentation using the Hohenheim Gas Test in order to identify the most inert emulsifier. Rumen fluids were collected from three non-lactating Original Brown-Swiss cannulated cows before morning feeding and incubated for 24 h with a basal diet in triplicates. The emulsifiers tested were ethanol, ethyl acetate, propylene glycol, glycerol, ethylene glycol, soy lecithin, and Tween® 80, each in two dosages (0.5% or 1% v/v). The untreated basal diet served as control. Compared to control, in vitro organic matter digestibility was enhanced by ethyl acetate (by 36.9 and 48.2%), ethylene glycol (by 20.6 and 20.1%), glycerol (by 46.9 and 56.8%) and soy lecithin (by 19.7 and 26.8%) at 0.5 and 1% dosage, respectively. Additionally, the 24-h methane production increased for ethanol (by 41.9 and 46.2%), ethylene glycol (by 50.5 and 51.5%), and glycerol (by 63.1 and 65.4%) for the 0.5 and 1% dosage, respectively, and 0.5% dosage for ethyl acetate (by 31.6%). The acetate molar proportion was 17.2%pt higher for ethyl acetate, and 25.5%pt lower for glycerol at 1% dosage, compared to the control. The propionate concentration was 22.1%pt higher 1% glycerol, and 15.2%pt and 15.1%pt higher for 0.5 and 1% propylene glycol, respectively, compared to the control. In summary, Tween® 80 did not significantly affect in vitro rumen fermentation parameters, making it the most suitable choice for in vitro incubations involving lipophilic substances in rumen fluid. Ethanol may be considered as an alternative emulsifier if methane production is not the variable of interest.

Candidatus Methanosphaera massiliense sp. nov., a methanogenic archaeal species found in a human fecal sample and prevalent in pigs and red kangaroos

Methanosphaera stadtmanae was the sole Methanosphaera representative to be cultured and detected by molecular methods in the human gut microbiota, further associated with digestive and respiratory diseases, leaving unknown the actual diversity of human-associated Methanosphaera species. Here, a novel Methanosphaera species, Candidatus Methanosphaera massiliense (Ca. M. massiliense) sp. nov. was isolated by culture using a hydrogen- and carbon dioxide-free medium from one human feces sample. Ca. M. massiliense is a non-motile, 850 nm Gram-positive coccus autofluorescent at 420 nm. Whole-genome sequencing yielded a 29.7% GC content, gapless 1,785,773 bp genome sequence with an 84.5% coding ratio, encoding for alcohol and aldehyde dehydrogenases promoting the growth of Ca. M. massiliense without hydrogen. Screening additional mammal and human feces using a specific genome sequence-derived DNA-polymerase RT-PCR system yielded a prevalence of 22% in pigs, 12% in red kangaroos, and no detection in 149 other human samples. This study, extending the diversity of Methanosphaera in human microbiota, questions the zoonotic sources of Ca. M. massiliense and possible transfer between hosts.IMPORTANCEMethanogens are constant inhabitants in the human gut microbiota in which Methanosphaera stadtmanae was the only cultivated Methanosphaera representative. We grew Candidatus Methanosphaera massiliense sp. nov. from one human feces sample in a novel culture medium under a nitrogen atmosphere. Systematic research for methanogens in human and animal fecal samples detected Ca. M. massiliense in pig and red kangaroo feces, raising the possibility of its zoonotic acquisition. Host specificity, source of acquisition, and adaptation of methanogens should be further investigated.

The evolving role of methanogenic archaea in mammalian microbiomes

Methanogenic archaea (methanogens) represent a diverse group of microorganisms that inhabit various environmental and host-associated microbiomes. These organisms play an essential role in global carbon cycling given their ability to produce methane, a potent greenhouse gas, as a by-product of their energy production. Recent advances in culture-independent and -dependent studies have highlighted an increased prevalence of methanogens in the host-associated microbiome of diverse animal species. Moreover, there is increasing evidence that methanogens, and/or the methane they produce, may play a substantial role in human health and disease. This review addresses the expanding host-range and the emerging view of host-specific adaptations in methanogen biology and ecology, and the implications for host health and disease.

Integrating Omics Technologies for a Comprehensive Understanding of the Microbiome and Its Impact on Cattle Production

Ruminant production holds a pivotal position within the global animal production and agricultural sectors. As population growth escalates, posing environmental challenges, a heightened emphasis is directed toward refining ruminant production systems. Recent investigations underscore the connection between the composition and functionality of the rumen microbiome and economically advantageous traits in cattle. Consequently, the development of innovative strategies to enhance cattle feed efficiency, while curbing environmental and financial burdens, becomes imperative. The advent of omics technologies has yielded fresh insights into metabolic health fluctuations in dairy cattle, consequently enhancing nutritional management practices. The pivotal role of the rumen microbiome in augmenting feeding efficiency by transforming low-quality feedstuffs into energy substrates for the host is underscored. This microbial community assumes focal importance within gut microbiome studies, contributing indispensably to plant fiber digestion, as well as influencing production and health variability in ruminants. Instances of compromised animal welfare can substantially modulate the microbiological composition of the rumen, thereby influencing production rates. A comprehensive global approach that targets both cattle and their rumen microbiota is paramount for enhancing feed efficiency and optimizing rumen fermentation processes. This review article underscores the factors that contribute to the establishment or restoration of the rumen microbiome post perturbations and the intricacies of host-microbiome interactions. We accentuate the elements responsible for responsible host-microbiome interactions and practical applications in the domains of animal health and production. Moreover, meticulous scrutiny of the microbiome and its consequential effects on cattle production systems greatly contributes to forging more sustainable and resilient food production systems, thereby mitigating the adverse environmental impact.

Novel complete methanogenic pathways in longitudinal genomic study of monogastric age-associated archaea

BACKGROUND

Archaea perform critical roles in the microbiome system, including utilizing hydrogen to allow for enhanced microbiome member growth and influencing overall host health. With the majority of microbiome research focusing on bacteria, the functions of archaea are largely still under investigation. Understanding methanogenic functions during the host lifetime will add to the limited knowledge on archaeal influence on gut and host health. In our study, we determined lifelong archaea dynamics, including detection and methanogenic functions, while assessing global, temporal and host distribution of our novel archaeal metagenome-assembled genomes (MAGs). We followed 7 monogastric swine throughout their life, from birth to adult (1-156 days of age), and collected feces at 22 time points. The samples underwent gDNA extraction, Illumina sequencing, bioinformatic quality and assembly processes, MAG taxonomic assignment and functional annotation. MAGs were utilized in downstream phylogenetic analysis for global, temporal and host distribution in addition to methanogenic functional potential determination.

RESULTS

We generated 1130 non-redundant MAGs, representing 588 unique taxa at the species level, with 8 classified as methanogenic archaea. The taxonomic classifications were as follows: orders Methanomassiliicoccales (5) and Methanobacteriales (3); genera UBA71 (3), Methanomethylophilus (1), MX-02 (1), and Methanobrevibacter (3). We recovered the first US swine Methanobrevibacter UBA71 sp006954425 and Methanobrevibacter gottschalkii MAGs. The Methanobacteriales MAGs were identified primarily during the young, preweaned host whereas Methanomassiliicoccales primarily in the adult host. Moreover, we identified our methanogens in metagenomic sequences from Chinese swine, US adult humans, Mexican adult humans, Swedish adult humans, and paleontological humans, indicating that methanogens span different hosts, geography and time. We determined complete metabolic pathways for all three methanogenic pathways: hydrogenotrophic, methylotrophic, and acetoclastic. This study provided the first evidence of acetoclastic methanogenesis in archaea of monogastric hosts which indicated a previously unknown capability for acetate utilization in methanogenesis for monogastric methanogens. Overall, we hypothesized that the age-associated detection patterns were due to differential substrate availability via the host diet and microbial metabolism, and that these methanogenic functions are likely crucial to methanogens across hosts. This study provided a comprehensive, genome-centric investigation of monogastric-associated methanogens which will further improve our understanding of microbiome development and functions.

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

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 JH1^T 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 JH1^T without pressurised H₂, using a variety of short chain alcohols. The results demonstrate that in the absence of H₂, JHI^T 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 JH1^T 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.

Isolation and characterisation of novel Methanocorpusculum species indicates the genus is ancestrally host-associated

BACKGROUND

With an increasing interest in the manipulation of methane produced from livestock cultivation, the microbiome of Australian marsupials provides a unique ecological and evolutionary comparison with 'low-methane' emitters. Previously, marsupial species were shown to be enriched for novel lineages of Methanocorpusculum, as well as Methanobrevibacter, Methanosphaera, and Methanomassiliicoccales. Despite sporadic reports of Methanocorpusculum from stool samples of various animal species, there remains little information on the impacts of these methanogens on their hosts.

RESULTS

Here, we characterise novel host-associated species of Methanocorpusculum, to explore unique host-specific genetic factors and their associated metabolic potential. We performed comparative analyses on 176 Methanocorpusculum genomes comprising 130 metagenome-assembled genomes (MAGs) recovered from 20 public animal metagenome datasets and 35 other publicly available Methanocorpusculum MAGs and isolate genomes of host-associated and environmental origin. Nine MAGs were also produced from faecal metagenomes of the common wombat (Vombatus ursinus) and mahogany glider (Petaurus gracilis), along with the cultivation of one axenic isolate from each respective animal; M. vombati (sp. nov.) and M. petauri (sp. nov.).

CONCLUSIONS

Through our analyses, we substantially expand the available genetic information for this genus by describing the phenotypic and genetic characteristics of 23 host-associated species of Methanocorpusculum. These lineages display differential enrichment of genes associated with methanogenesis, amino acid biosynthesis, transport system proteins, phosphonate metabolism, and carbohydrate-active enzymes. These results provide insights into the differential genetic and functional adaptations of these novel host-associated species of Methanocorpusculum and suggest that this genus is ancestrally host-associated.

Methyl-Based Methanogenesis: an Ecological and Genomic Review

Methyl-based methanogenesis is one of three broad categories of archaeal anaerobic methanogenesis, including both the methyl dismutation (methylotrophic) pathway and the methyl-reducing (also known as hydrogen-dependent methylotrophic) pathway. Methyl-based methanogenesis is increasingly recognized as an important source of methane in a variety of environments. Here, we provide an overview of methyl-based methanogenesis research, including the conditions under which methyl-based methanogenesis can be a dominant source of methane emissions, experimental methods for distinguishing different pathways of methane production, molecular details of the biochemical pathways involved, and the genes and organisms involved in these processes. We also identify the current gaps in knowledge and present a genomic and metagenomic survey of methyl-based methanogenesis genes, highlighting the diversity of methyl-based methanogens at multiple taxonomic levels and the widespread distribution of known methyl-based methanogenesis genes and families across different environments.

Competitive Reactions during Ethanol Chain Elongation Were Temporarily Suppressed by Increasing Hydrogen Partial Pressure through Methanogenesis Inhibition

Organic waste streams can be converted into high-value platform chemicals such as medium-chain carboxylic acids (MCCAs) using mixed microbial communities via chain elongation. However, the heterogeneity of waste streams and the use of complex microbial communities can lead to undesirable reactions, thus decreasing process efficiency. We explored suppressing excessive ethanol oxidation to acetate (EEO) by increasing the hydrogen partial pressure (PH2) through hydrogenotrophic methanogenesis inhibition by periodically adding 2-bromoethanesulfonate (2-BES) to an MCCA-producing bioreactor to reach 10 mM of 2-BES upon addition. The bioreactor was fed with pretreated food waste and brewery waste containing high concentrations of short-chain carboxylic acids and ethanol, respectively. While 2-BES addition initially reduced EEO, some methanogens (Methanobrevibacter spp.) persisted and resistant populations were selected over time. Besides changing the methanogenic community structure, adding 2-BES also changed the bacterial community structure due to its impact on PH2. While we demonstrated that PH2 could be manipulated using 2-BES to control EEO, methods that do not require the addition of a chemical inhibitor should be explored to maintain optimum PH2 for long-term suppression of EEO.

Ecology of Methanonatronarchaeia

Methanonatronarchaeia represents a deep-branching phylogenetic lineage of extremely halo(alkali)philic and moderately thermophilic methyl-reducing methanogens belonging to the phylum Halobacteriota. It includes two genera, the alkaliphilic Methanonatronarchaeum and the neutrophilic Ca. Methanohalarchaeum. The former is represented by multiple closely related pure culture isolates from hypersaline soda lakes, while the knowledge about the latter is limited to a few mixed cultures with anaerobic haloarchaea. To get more insight into the distribution and ecophysiology of this enigmatic group of extremophilic methanogens, potential activity tests and enrichment cultivation with different substrates and at different conditions were performed with anaerobic sediment slurries from various hypersaline lakes in Russia. Methanonatronarchaeum proliferated exclusively in hypersaline soda lake samples mostly at elevated temperature, while at mesophilic conditions it coexisted with the extremely salt-tolerant methylotroph Methanosalsum natronophilum. Methanonatronarchaeum was also able to serve as a methylotrophic or hydrogenotrophic partner in several thermophilic enrichment cultures with fermentative bacteria. Ca. Methanohalarchaeum did not proliferate at mesophilic conditions and at thermophilic conditions it competed with extremely halophilic and moderately thermophilic methylotroph Methanohalobium, which it outcompeted at a combination of elevated temperature and methyl-reducing conditions. Overall, the results demonstrated that Methanonatronarchaeia are specialized extremophiles specifically proliferating in conditions of elevated temperature coupled with extreme salinity and simultaneous availability of a wide range of C1 -methylated compounds and H2 /formate.

A catalogue of 1,167 genomes from the human gut archaeome

The human gut microbiome plays an important role in health, but its archaeal diversity remains largely unexplored. In the present study, we report the analysis of 1,167 nonredundant archaeal genomes (608 high-quality genomes) recovered from human gastrointestinal tract, sampled across 24 countries and rural and urban populations. We identified previously undescribed taxa including 3 genera, 15 species and 52 strains. Based on distinct genomic features, we justify the split of the Methanobrevibacter smithii clade into two separate species, with one represented by the previously undescribed 'Candidatus Methanobrevibacter intestini'. Patterns derived from 28,581 protein clusters showed significant associations with sociodemographic characteristics such as age groups and lifestyle. We additionally show that archaea are characterized by specific genomic and functional adaptations to the host and carry a complex virome. Our work expands our current understanding of the human archaeome and provides a large genome catalogue for future analyses to decipher its impact on human physiology.

The rumen microbiome inhibits methane formation through dietary choline supplementation

Enteric fermentation from ruminants is a primary source of anthropogenic methane emission. This study aims to add another approach for methane mitigation by manipulation of the rumen microbiome. Effects of choline supplementation on methane formation were quantified in vitro using the Rumen Simulation Technique. Supplementing 200 mM of choline chloride or choline bicarbonate reduced methane emissions by 97–100% after 15 days. Associated with the reduction of methane formation, metabolomics analysis revealed high post-treatment concentrations of ethanol, which likely served as a major hydrogen sink. Metagenome sequencing showed that the methanogen community was almost entirely lost, and choline-utilizing bacteria that can produce either lactate, ethanol or formate as hydrogen sinks were enriched. The taxa most strongly associated with methane mitigation were Megasphaera elsdenii and Denitrobacterium detoxificans, both capable of consuming lactate, which is an intermediate product and hydrogen sink. Accordingly, choline metabolism promoted the capability of bacteria to utilize alternative hydrogen sinks leading to a decline of hydrogen as a substrate for methane formation. However, fermentation of fibre and total organic matter could not be fully maintained with choline supplementation, while amino acid deamination and ethanolamine catabolism produced excessive ammonia, which would reduce feed efficiency and adversely affect live animal performance.

Comparative Microbiome Analysis Reveals the Ecological Relationships Between Rumen Methanogens, Acetogens, and Their Hosts

Ruminant methane, which is generated by methanogens through the consumption of hydrogen and supports the normal function of the rumen ecosystem, is a major source of greenhouse gases. Reductive acetogenesis by acetogens is a possible alternative sink that can dispose of hydrogen for acetate production. However, the distribution of rumen methanogens and acetogens along with the relationships among methanogens, acetogens, and their host are poorly understood. Therefore, we investigated the rumen methanogen and acetogen communities of 97 individual animals representing 14 ruminant species within three ruminant families Cervidae (deer), Bovidae (bovid), and Moschidae (musk deer). The results showed that the Methanobrevibacter spp. and acetogens associated with Eubacteriaceae were the most widespread methanogens and acetogens, respectively. However, other methanogens and acetogens exhibited host specificity in the rumen of reindeer and Chinese muntjac deer. Acetogen and methanogen communities were not correlated in these species, and the phylosymbiosis signature between host phylogeny and the composition of both communities was lacking. The abundance of Methanobrevibacter gottschalkii was negatively correlated with the degree of papillation of the rumen wall. Finally, co-occurrence analysis showed that the variation of the predicted methane yields was characterized by the interactive patterns between methanogens, acetogens, and concentrations of rumen metabolites. Our results show that rumen methanogen and acetogen communities have low compositional interdependence and do not exhibit parallel host evolution, which suggests that the strategies for mitigating methane production should be based on a species-specific rumen microbiota analysis.

Several ways one goal-methanogenesis from unconventional substrates

Abstract

Methane is the second most important greenhouse gas on earth. It is produced by methanogenic archaea, which play an important role in the global carbon cycle. Three main methanogenesis pathways are known: in the hydrogenotrophic pathway H₂ and carbon dioxide are used for methane production, whereas in the methylotrophic pathway small methylated carbon compounds like methanol and methylated amines are used. In the aceticlastic pathway, acetate is disproportionated to methane and carbon dioxide. However, next to these conventional substrates, further methanogenic substrates and pathways have been discovered. Several phylogenetically distinct methanogenic lineages (Methanosphaera, Methanimicrococcus, Methanomassiliicoccus, Methanonatronarchaeum) have evolved hydrogen-dependent methylotrophic methanogenesis without the ability to perform either hydrogenotrophic or methylotrophic methanogenesis. Genome analysis of the deep branching Methanonatronarchaeum revealed an interesting membrane-bound hydrogenase complex affiliated with the hardly described class 4 g of multisubunit hydrogenases possibly providing reducing equivalents for anabolism. Furthermore, methylated sulfur compounds such as methanethiol, dimethyl sulfide, and methylmercaptopropionate were described to be converted into adapted methylotrophic methanogenesis pathways of Methanosarcinales strains. Moreover, recently it has been shown that the methanogen Methermicoccus shengliensis can use methoxylated aromatic compounds in methanogenesis. Also, tertiary amines like choline (N,N,N-trimethylethanolamine) or betaine (N,N,N-trimethylglycine) have been described as substrates for methane production in Methanococcoides and Methanolobus strains. This review article will provide in-depth information on genome-guided metabolic reconstructions, physiology, and biochemistry of these unusual methanogenesis pathways.

Key points

• Newly discovered methanogenic substrates and pathways are reviewed for the first time.

• The review provides an in-depth analysis of unusual methanogenesis pathways.

• The hydrogenase complex of the deep branching Methanonatronarchaeum is analyzed.

Occurrence and expression of genes encoding methyl-compound production in rumen bacteria

Background

Digestive processes in the rumen lead to the release of methyl-compounds, mainly methanol and methylamines, which are used by methyltrophic methanogens to form methane, an important agricultural greenhouse gas. Methylamines are produced from plant phosphatidylcholine degradation, by choline trimethylamine lyase, while methanol comes from demethoxylation of dietary pectins via pectin methylesterase activity. We have screened rumen metagenomic and metatranscriptomic datasets, metagenome assembled genomes, and the Hungate1000 genomes to identify organisms capable of producing methyl-compounds. We also describe the enrichment of pectin-degrading and methane-forming microbes from sheep rumen contents and the analysis of their genomes via metagenomic assembly.

Results

Screens of metagenomic data using the protein domains of choline trimethylamine lyase (CutC), and activator protein (CutD) found good matches only to Olsenella umbonata and to Caecibacter, while the Hungate1000 genomes and metagenome assembled genomes from the cattle rumen found bacteria within the phyla Actinobacteria, Firmicutes and Proteobacteria. The cutC and cutD genes clustered with genes that encode structural components of bacterial microcompartment proteins. Prevotella was the dominant genus encoding pectin methyl esterases, with smaller numbers of sequences identified from other fibre-degrading rumen bacteria. Some large pectin methyl esterases (> 2100 aa) were found to be encoded in Butyrivibrio genomes. The pectin-utilising, methane-producing consortium was composed of (i) a putative pectin-degrading bacterium (phylum Tenericutes, class Mollicutes), (ii) a galacturonate-using Sphaerochaeta sp. predicted to produce acetate, lactate, and ethanol, and (iii) a methylotrophic methanogen, Methanosphaera sp., with the ability to form methane via a primary ethanol-dependent, hydrogen-independent, methanogenesis pathway.

Conclusions

The main bacteria that produce methyl-compounds have been identified in ruminants. Their enzymatic activities can now be targeted with the aim of finding ways to reduce the supply of methyl-compound substrates to methanogens, and thereby limit methylotrophic methanogenesis in the rumen.

Energy Conservation and Hydrogenase Function in Methanogenic Archaea, in Particular the Genus Methanosarcina

The biological production of methane is vital to the global carbon cycle and accounts for ca. 74% of total methane emissions. The organisms that facilitate this process, methanogenic archaea, belong to a large and phylogenetically diverse group that thrives in a wide range of anaerobic environments. Two main subgroups exist within methanogenic archaea: those with and those without cytochromes. Although a variety of metabolisms exist within this group, the reduction of growth substrates to methane using electrons from molecular hydrogen is, in a phylogenetic sense, the most widespread methanogenic pathway. Methanogens without cytochromes typically generate methane by the reduction of CO₂ with electrons derived from H₂, formate, or secondary alcohols, generating a transmembrane ion gradient for ATP production via an Na⁺-translocating methyltransferase (Mtr). These organisms also conserve energy with a novel flavin-based electron bifurcation mechanism, wherein the endergonic reduction of ferredoxin is facilitated by the exergonic reduction of a disulfide terminal electron acceptor coupled to either H₂ or formate oxidation. Methanogens that utilize cytochromes have a broader substrate range, and can convert acetate and methylated compounds to methane, in addition to the ability to reduce CO₂ Cytochrome-containing methanogens are able to supplement the ion motive force generated by Mtr with an H⁺-translocating electron transport system. In both groups, enzymes known as hydrogenases, which reversibly interconvert protons and electrons to molecular hydrogen, play a central role in the methanogenic process. This review discusses recent insight into methanogen metabolism and energy conservation mechanisms with a particular focus on the genus Methanosarcina.

Do different livestock dwellings on single grassland share similar faecal microbial communities?

Huge numbers of microorganisms reside in livestock faeces and constitute one of the most complex microbial ecosystems. Here, faecal microbial communities of three typical livestock in Xilingol steppe grassland, i.e. sheep, cattle, and horse, were investigated by Illumina MiSeq sequencing and quantitative real-time polymerase chain reaction (qPCR). Firmicutes and Bacteroidetes comprised the majority of bacterial communities in three livestock faeces. Sordariomycetes, Leotiomycetes, and Dothideomycetes were dominant in fungal communities, as well as Methanobacteria and Methanomicrobia were dominant in archaeal communities in three livestock faeces. Similar fungal community dominated in these samples, with 95.51% of the sequences falling into the overlap of three livestock faeces. In contrast, bacterial communities were quite variable among three different livestock faeces, but a similar community was observed in sheep and cattle faeces. Nearly all the archaea were identified as methanogens, whilst the most diverse and abundant methanogens were detected in cattle faeces. Potential pathogens including Bacteroides spp., Desulfovibrio spp., and Fusarium spp. were also detected in livestock faeces. Overall, this study provides the first detailed microbial comparison of typical livestock faeces dwelling on single grassland, and may be help guide management strategies for livestock grazing and grassland restoration.

Comparative Genomic Analysis of Members of the Genera Methanosphaera and Methanobrevibacter Reveals Distinct Clades with Specific Potential Metabolic Functions

Methanobrevibacter and Methanosphaera species represent some of the most prevalent methanogenic archaea in the gastrointestinal tract of animals and humans and play an important role in this environment. The aim of this study was to identify genomic features that are shared or specific for members of each genus with a special emphasis of the analysis on the assimilation of nitrogen and acetate and the utilization of methanol and ethanol for methanogenesis. Here, draft genome sequences of Methanobrevibacter thaueri strain DSM 11995^T, Methanobrevibacter woesei strain DSM 11979^T, and Methanosphaera cuniculi strain 4103^T are reported and compared to those of 16 other Methanobrevibacter and Methanosphaera genomes, including genomes of the 13 currently available types of strains of the two genera. The comparative genome analyses indicate that among other genes, the absence of molybdopterin cofactor biosynthesis is conserved in Methanosphaera species but reveals also that the three species share a core set of more than 300 genes that distinguishes the genus Methanosphaera from the genus Methanobrevibacter. Multilocus sequence analysis shows that the genus Methanobrevibacter can be subdivided into clades, potentially new genera, which may display characteristic specific metabolic features. These features include not only the potential ability of nitrogen fixation and acetate assimilation in a clade comprised of Methanobrevibacter species from the termite gut and Methanobrevibacter arboriphilus strains but also the potential capability to utilize ethanol and methanol in a clade comprising Methanobrevibacter wolinii strain DSM 11976^T, Mbb. sp. AbM4, and Mbb. boviskoreani strain DSM 25824^T.

3-NOP vs. Halogenated Compound: Methane Production, Ruminal Fermentation and Microbial Community Response in Forage Fed Cattle

The aim of this study was to investigate the effects of 3-nitrooxypropanol (3-NOP) and chloroform on methane (CH₄) and H₂ production, ruminal metabolites and microbial community structure in cattle fed a tropical forage diet. Eight rumen-fistulated steers were fed a roughage hay diet (Rhodes grass; Chloris gayana) for 31 days (control period). Four animals received the antimethanogenic compound chloroform (1.6 g chloroform-cyclodextrin/100 kg live weight (LW)) while the other four received 3-NOP (2.5 g 3-NOP/animal/day) for 21 days. Methane decrease compared with control period was similar for both treatments (30-38%) with no differences for expelled H₂ between controls and treatments. Daily weight gain (DWG) was significantly increased when animals were treated with 3-NOP compared with chloroform and control. Regarding the ruminal fermentation parameters increases in ammonia, acetate and branched chain fatty acids were observed with both compounds compared with the controls. Also, methylamines, alcohols and dimethyl sulfone (DMSO₂) concentrations were significantly increased with the treatments compared with control, being greater with 3-NOP. The rumen microbial analyses revealed a similar profile for both treatments, with a shift in operational taxonomic units (OTUs) assigned to the Prevotellaceae and Campylobacteraceae family. Moreover, major archaeal OTUs associated with Methanobrevibacter and Methanosphaera were significantly affected to varying extents based on the inhibitory treatments compared to the control. The abundance of the Methanobrevibacter spp. was decreased by 3-NOP and chloroform, while the Methanomassiliicoccaceae family was inhibited only by 3-NOP. The results suggest that despite the specific mode of action of 3-NOP on methanogens, inhibition of methanogenesis by both compounds resulted in similar responses in metabolism and microbial community structure in the rumen. We hypothesized that these changes were driven by the redirection of metabolic hydrogen ([H]) by both treatments. Therefore results from previous publications using chloroform as an inhibitor of methanogenesis may be useful in predicting ruminal microbiota and fermentation responses to 3-NOP.

Culture- and metagenomics-enabled analyses of the Methanosphaera genus reveals their monophyletic origin and differentiation according to genome size

The genus Methanosphaera is a well-recognized but poorly characterized member of the mammalian gut microbiome, and distinctive from Methanobrevibacter smithii for its ability to induce a pro-inflammatory response in humans. Here we have used a combination of culture- and metagenomics-based approaches to expand the representation and information for the genus, which has supported the examination of their phylogeny and physiological capacity. Novel isolates of the genus Methanosphaera were recovered from bovine rumen digesta and human stool, with the bovine isolate remarkable for its large genome size relative to other Methanosphaera isolates from monogastric hosts. To substantiate this observation, we then recovered seven high-quality Methanosphaera-affiliated population genomes from ruminant and human gut metagenomic datasets. Our analyses confirm a monophyletic origin of Methanosphaera spp. and that the colonization of monogastric and ruminant hosts favors representatives of the genus with different genome sizes, reflecting differences in the genome content needed to persist in these different habitats.

Assembly of 913 microbial genomes from metagenomic sequencing of the cow rumen

The cow rumen is adapted for the breakdown of plant material into energy and nutrients, a task largely performed by enzymes encoded by the rumen microbiome. Here we present 913 draft bacterial and archaeal genomes assembled from over 800 Gb of rumen metagenomic sequence data derived from 43 Scottish cattle, using both metagenomic binning and Hi-C-based proximity-guided assembly. Most of these genomes represent previously unsequenced strains and species. The draft genomes contain over 69,000 proteins predicted to be involved in carbohydrate metabolism, over 90% of which do not have a good match in public databases. Inclusion of the 913 genomes presented here improves metagenomic read classification by sevenfold against our own data, and by fivefold against other publicly available rumen datasets. Thus, our dataset substantially improves the coverage of rumen microbial genomes in the public databases and represents a valuable resource for biomass-degrading enzyme discovery and studies of the rumen microbiome.

Anaerobic co-digestion of pig manure and food waste; effects on digestate biosafety, dewaterability, and microbial community dynamics

This study assessed the effect of varying pig manure (PM)/food waste (FW) mixing ratio and hydraulic retention time (HRT) on methane yields, digestate dewaterability, enteric indicator bacteria and microbial communities during anaerobic co-digestion. Three 10 L digesters were operated at 39 °C, each with a PM/FW feedstock composition of 85%/15%, 63%/37% and 40%/60% (volatile solids basis). While the PM/FW ratio was different among reactors, the organic loading rate applied was equal, and increased stepwise with reducing HRT. The effects of three different HRTs were studied: 41, 29, and 21 days. Increasing the proportion of FW in the feedstock significantly increased methane yields, but had no significant effect on counts of enteric indicator bacteria in the digestate or specific resistance to filtration, suggesting that varying the PM/FW feedstock composition at the mixing ratios studied should not have major consequences for digestate disposal. Decreasing HRT significantly increased volumetric methane yields, increased digestate volatile solids concentrations and increased the proportion of particles >500 µm in the digestate, indicating that decreasing HRT to 21 days reduced methane conversion efficiency High throughput 16S rRNA sequencing data revealed that microbial communities were just slightly affected by changes in digester operating conditions. These results would provide information useful when optimizing the start-up and operation of biogas plants treating these substrates.

The Draft Genome of the Non-Host-Associated Methanobrevibacter arboriphilus Strain DH1 Encodes a Large Repertoire of Adhesin-Like Proteins

Methanobrevibacter arboriphilus strain DH1 is an autotrophic methanogen that was isolated from the wetwood of methane-emitting trees. This species has been of considerable interest for its unusual oxygen tolerance and has been studied as a model organism for more than four decades. Strain DH1 is closely related to other host-associated Methanobrevibacter species from intestinal tracts of animals and the rumen, making this strain an interesting candidate for comparative analysis to identify factors important for colonizing intestinal environments. Here, the genome sequence of M. arboriphilus strain DH1 is reported. The draft genome is composed of 2.445.031 bp with an average GC content of 25.44% and predicted to harbour 1964 protein-encoding genes. Among the predicted genes, there are also more than 50 putative genes for the so-called adhesin-like proteins (ALPs). The presence of ALP-encoding genes in the genome of this non-host-associated methanogen strongly suggests that target surfaces for ALPs other than host tissues also need to be considered as potential interaction partners. The high abundance of ALPs may also indicate that these types of proteins are more characteristic for specific phylogenetic groups of methanogens rather than being indicative for a particular environment the methanogens thrives in.