Ninety-nine de novo assembled genomes from the moose (Alces alces) rumen microbiome provide new insights into microbial plant biomass degradation

Characterization of a novel multifunctional glycoside hydrolase family in the metagenome-assembled genomes of horse gut

The gut microbiota is a treasure trove of carbohydrate-active enzymes (CAZymes). To explore novel and efficient CAZymes, we analyzed the 4,142 metagenome-assembled genomes (MAGs) of the horse gut microbiota and found the MAG117.bin13 genome (Bacteroides fragilis) contains the highest number of polysaccharide utilisation loci sites (PULs), indicating its high capability for carbohydrate degradation. Bioinformatics analysis indicate that the PULs region of the MAG117.bin13 genome encodes many hypothetical proteins, which are important sources for exploring novel CAZymes. Interestingly, we discovered a hypothetical protein (595 amino acids). This protein exhibits potential CAZymes activity and has a lower similarity to CAZymes, we named it BfLac2275. We purified the protein using prokaryotic expression technology and studied its enzymatic function. The hydrolysis experiment of the polysaccharide substrate showed that the BfLac2275 protein has the ability to degrade α-lactose (156.94 U/mg), maltose (92.59 U/mg), raffinose (86.81 U/mg), and hyaluronic acid (5.71 U/mg). The enzyme activity is optimal at pH 5.0 and 30 ℃, indicating that the hypothetical protein BfLac2275 is a novel and multifunctional CAZymes in the glycoside hydrolases (GHs). These properties indicate that BfLac2275 has broad application prospects in many fields such as plant polysaccharide decomposition, food industry, animal feed additives and enzyme preparations. This study not only serves as a reference for exploring novel CAZymes encoded by gut microbiota but also provides an example for further studying the functional annotation of hypothetical genes in metagenomic assembly genomes.

Enhancing Photosynthetic Carbon Transport in Rice Plant Optimizes Rhizosphere Bacterial Community in Saline Soil

Saline soils exert persistent salt stress on plants that inhibits their ability to carry out photosynthesis and leads to photosynthetic carbon (C) scarcity in plant roots and the rhizosphere. However, it remains unclear how a rhizosphere environment is shaped by photosynthetic C partitioning under saline conditions. Given that sucrose is the primary form of photosynthetic C transport, we, respectively, created sucrose transport distorted (STD) and enhanced (STE) rice lines through targeted mutation and overexpression of the sucrose transporter gene OsSUT5. This approach allowed us to investigate different scenarios of photosynthate partitioning to the rhizosphere. Compared to the non-saline soil, we found a significant decrease in soil dissolved organic carbon (DOC) in the rhizosphere, associated with a reduction in bacterial diversity when rice plants were grown under moderate saline conditions. These phenomena were sharpened with STD plants but were largely alleviated in the rhizosphere of STE plants, in which the rhizosphere DOC, and the diversity and abundances of dominant bacterial phyla were measured at comparable levels to the wildtype plants under non-saline conditions. The complexity of bacteria showed a greater level in the rhizosphere of STE plants grown under saline conditions. Several salt-tolerant genera, such as Halobacteroidaceae and Zixibacteria, were found to colonize the rhizosphere of STE plants that could contribute to improved rice growth under persistent saline stresses, due to an increase in C deposition.

A metagenomic catalogue of the ruminant gut archaeome

While the ruminant gut archaeome regulates the gut microbiota and hydrogen balance, it is also a major producer of the greenhouse gas methane. However, ruminant gut archaeome diversity within the gastrointestinal tract (GIT) of ruminant animals worldwide remains largely underexplored. Here, we construct a catalogue of 998 unique archaeal genomes recovered from the GITs of ruminants, utilizing 2270 metagenomic samples across 10 different ruminant species. Most of the archaeal genomes (669/998 = 67.03%) belong to Methanobacteriaceae and Methanomethylophilaceae (198/998 = 19.84%). We recover 47/279 previously undescribed archaeal genomes at the strain level with completeness of >80% and contamination of <5%. We also investigate the archaeal gut biogeography across various ruminants and demonstrate that archaeal compositional similarities vary significantly by breed and gut location. The catalogue contains 42,691 protein clusters, and the clustering and methanogenic pathway analysis reveal strain- and host-specific dependencies among ruminant animals. We also find that archaea potentially carry antibiotic and metal resistance genes, mobile genetic elements, virulence factors, quorum sensors, and complex archaeal viromes. Overall, this catalogue is a substantial repository for ruminant archaeal recourses, providing potential for advancing our understanding of archaeal ecology and discovering strategies to regulate methane production in ruminants.

Functions and mechanisms of nonstarch polysaccharides in monogastric animal production

As natural active ingredients, polysaccharides are a class of biological macromolecules that are ubiquitous in living organisms and have antibacterial, antioxidant, antitumor and intestinal flora-regulating functions. Nonstarch polysaccharides (NSPs) are an important class of polysaccharides that include both soluble and insoluble nonstarch polysaccharides. As green feed additives, NSPs play important roles in promoting immunity and disease resistance in the body, regulating the intestinal microbial balance and improving the quality of animal products. NSPs regulate cell signal transduction mainly via interactions between short-chain fatty acids and G protein-coupled receptors and inhibiting the histone deacetylation pathway to protect the intestinal barrier in animals. In this paper, the composition, physiological functions, and molecular mechanisms of the gut protective effects of NSPs are reviewed to provide a reference for the application of NSPs in monogastric animal production.

Soil microbiome characterization and its future directions with biosensing

Soil microbiome characterization is typically achieved with next-generation sequencing (NGS) techniques. Metabarcoding is very common, and meta-omics is growing in popularity. These techniques have been instrumental in microbiology, but they have limitations. They require extensive time, funding, expertise, and computing power to be effective. Moreover, these techniques are restricted to controlled laboratory conditions; they are not applicable in field settings, nor can they rapidly generate data. This hinders using NGS as an environmental monitoring tool or an in-situ checking device. Biosensing technology can be applied to soil microbiome characterization to overcome these limitations and to complement NGS techniques. Biosensing has been used in biomedical applications for decades, and many successful commercial products are on the market. Given its previous success, biosensing has much to offer soil microbiome characterization. There is a great variety of biosensors and biosensing techniques, and a few in particular are better suited for soil field studies. Aptamers are more stable than enzymes or antibodies and are more ready for field-use biosensors. Given that any microbiome is complex, a multiplex sensor will be needed, and with large, complicated datasets, machine learning might benefit these analyses. If the signals from the biosensors are optical, a smartphone can be used as a portable optical reader and potential data-analyzing device. Biosensing is a rich field that couples engineering and biology, and applying its toolset to help advance soil microbiome characterization would be a boon to microbiology more broadly.

Transient colonizing microbes promote gut dysbiosis and functional impairment

Species composition of the healthy adult gut microbiota tends to be stable over time. Destabilization of the gut microbiome under the influence of different factors is the main driver of the microbial dysbiosis and subsequent impacts on host physiology. Here, we used metagenomics data from a Swedish longitudinal cohort, to determine the stability of the gut microbiome and uncovered two distinct microbial species groups; persistent colonizing species (PCS) and transient colonizing species (TCS). We validated the continuation of this grouping, generating gut metagenomics data for additional time points from the same Swedish cohort. We evaluated the existence of PCS/TCS across different geographical regions and observed they are globally conserved features. To characterize PCS/TCS phenotypes, we performed bioreactor fermentation with faecal samples and metabolic modeling. Finally, using chronic disease gut metagenome and other multi-omics data, we identified roles of TCS in microbial dysbiosis and link with abnormal changes to host physiology.

Global compositional and functional states of the human gut microbiome in health and disease

The human gut microbiota is of increasing interest, with metagenomics a key tool for analyzing bacterial diversity and functionality in health and disease. Despite increasing efforts to expand microbial gene catalogs and an increasing number of metagenome-assembled genomes, there have been few pan-metagenomic association studies and in-depth functional analyses across different geographies and diseases. Here, we explored 6014 human gut metagenome samples across 19 countries and 23 diseases by performing compositional, functional cluster, and integrative analyses. Using interpreted machine learning classification models and statistical methods, we identified Fusobacterium nucleatum and Anaerostipes hadrus with the highest frequencies, enriched and depleted, respectively, across different disease cohorts. Distinct functional distributions were observed in the gut microbiomes of both westernized and nonwesternized populations. These compositional and functional analyses are presented in the open-access Human Gut Microbiome Atlas, allowing for the exploration of the richness, disease, and regional signatures of the gut microbiota across different cohorts.

Structural and functional analysis of the active cow rumen's microbial community provides a catalogue of genes and microbes participating in the deconstruction of cardoon biomass

BACKGROUND

Ruminal microbial communities enriched on lignocellulosic biomass have shown considerable promise for the discovery of microorganisms and enzymes involved in digesting cell wall compounds, a key bottleneck in the development of second-generation biofuels and bioproducts, enabling a circular bioeconomy. Cardoon (Cynara cardunculus) is a promising inedible energy crop for current and future cellulosic biorefineries and the emerging bioenergy and bioproducts industries. The rumen microbiome can be considered an anaerobic "bioreactor", where the resident microbiota carry out the depolymerization and hydrolysis of plant cell wall polysaccharides (PCWPs) through the catalytic action of fibrolytic enzymes. In this context, the rumen microbiota represents a potential source of microbes and fibrolytic enzymes suitable for biofuel production from feedstocks. In this study, metatranscriptomic and 16S rRNA sequencing were used to profile the microbiome and to investigate the genetic features within the microbial community adherent to the fiber fractions of the rumen content and to the residue of cardoon biomass incubated in the rumen of cannulated cows.

RESULTS

The metatranscriptome of the cardoon and rumen fibre-adherent microbial communities were dissected in their functional and taxonomic components. From a functional point of view, transcripts involved in the methanogenesis from CO2 and H2, and from methanol were over-represented in the cardoon-adherent microbial community and were affiliated with the Methanobrevibacter and Methanosphaera of the Euryarchaeota phylum. Transcripts encoding glycoside hydrolases (GHs), carbohydrate-binding modules (CBMs), carbohydrate esterases (CEs), polysaccharide lyases (PLs), and glycoside transferases (GTs) accounted for 1.5% (6,957) of the total RNA coding transcripts and were taxonomically affiliated to major rumen fibrolytic microbes, such as Oscillospiraceae, Fibrobacteraceae, Neocallimastigaceae, Prevotellaceae, Lachnospiraceae, and Treponemataceae. The comparison of the expression profile between cardoon and rumen fiber-adherent microbial communities highlighted that specific fibrolytic enzymes were potentially responsible for the breakdown of cardoon PCWPs, which was driven by specific taxa, mainly Ruminococcus, Treponema, and Neocallimastigaceae.

CONCLUSIONS

Analysis of 16S rRNA and metatranscriptomic sequencing data revealed that the cow rumen microbiome harbors a repertoire of new enzymes capable of degrading PCWPs. Our results demonstrate the feasibility of using metatranscriptomics of enriched microbial RNA as a potential approach for accelerating the discovery of novel cellulolytic enzymes that could be harnessed for biotechnology. This research contributes a relevant perspective towards degrading cellulosic biomass and providing an economical route to the production of advanced biofuels and high-value bioproducts.

A compendium of ruminant gastrointestinal phage genomes revealed a higher proportion of lytic phages than in any other environments

BACKGROUND

Ruminants are important livestock animals that have a unique digestive system comprising multiple stomach compartments. Despite significant progress in the study of microbiome in the gastrointestinal tract (GIT) sites of ruminants, we still lack an understanding of the viral community of ruminants. Here, we surveyed its viral ecology using 2333 samples from 10 sites along the GIT of 8 ruminant species.

RESULTS

We present the Unified Ruminant Phage Catalogue (URPC), a comprehensive survey of phages in the GITs of ruminants including 64,922 non-redundant phage genomes. We characterized the distributions of the phage genomes in different ruminants and GIT sites and found that most phages were organism-specific. We revealed that ~ 60% of the ruminant phages were lytic, which was the highest as compared with those in all other environments and certainly will facilitate their applications in microbial interventions. To further facilitate the future applications of the phages, we also constructed a comprehensive virus-bacteria/archaea interaction network and identified dozens of phages that may have lytic effects on methanogenic archaea.

CONCLUSIONS

The URPC dataset represents a useful resource for future microbial interventions to improve ruminant production and ecological environmental qualities. Phages have great potential for controlling pathogenic bacterial/archaeal species and reducing methane emissions. Our findings provide insights into the virome ecology research of the ruminant GIT and offer a starting point for future research on phage therapy in ruminants. Video Abstract.

Reference gene catalog and metagenome-assembled genomes from the gut microbiome reveal the microbial composition, antibiotic resistome, and adaptability of a lignocellulose diet in the giant panda

The giant panda, a strict herbivore that feeds on bamboo, still retains a typical carnivorous digestive system. Reference catalogs of microbial genes and genomes are lacking, largely limiting the antibiotic resistome and functional exploration of the giant panda gut microbiome. Here, we integrated 177 fecal metagenomes of captive and wild giant pandas to construct a giant panda integrated gene catalog (GPIGC) comprised of approximately 4.5 million non-redundant genes and reconstruct 393 metagenome-assembled genomes (MAGs). Taxonomic and functional characterization of genes revealed that the captivity of the giant panda significantly changed the core microbial composition and the distribution of microbial genes. Higher abundance and prevalence of antibiotic resistance genes (ARGs) were detected in the guts of captive giant pandas, and ARG distribution was influenced by geography, for both captive and wild individuals. Escherichia, as the prevalent genus in the guts of captive giant pandas, was the main carrier of ARGs, meaning there is a high risk of ARG transmission by Escherichia. We also found that multiple mcr gene variants, conferring plasmid-mediated mobile colistin resistance, were widespread in the guts of captive and wild giant pandas. There were low proportions of carbohydrate-active enzyme (CAZyme) genes in GPIGC and MAGs compared with several omnivorous and herbivorous mammals. Many members of Clostridium MAGs were significantly enriched in the guts of adult, old and wild giant pandas. The genomes of isolates and MAGs of Clostridiaceae harbored key genes or enzymes in complete pathways for degrading lignocellulose and producing short-chain fatty acids (SCFAs), indicating the potential of these bacteria to utilize the low-nutrient bamboo diet. Overall, our data presented an exhaustive reference gene catalog and MAGs in giant panda gut and provided a comprehensive understanding of the antibiotic resistome and microbial adaptability for a high-lignocellulose diet.

Rumen microbes, enzymes, metabolisms, and application in lignocellulosic waste conversion - A comprehensive review

The rumen of ruminants is a natural anaerobic fermentation system that efficiently degrades lignocellulosic biomass and mainly depends on synergistic interactions between multiple microbes and their secreted enzymes. Ruminal microbes have been employed as biomass waste converters and are receiving increasing attention because of their degradation performance. To explore the application of ruminal microbes and their secreted enzymes in biomass waste, a comprehensive understanding of these processes is required. Based on the degradation capacity and mechanism of ruminal microbes and their secreted lignocellulose enzymes, this review concentrates on elucidating the main enzymatic strategies that ruminal microbes use for lignocellulose degradation, focusing mainly on polysaccharide metabolism-related gene loci and cellulosomes. Hydrolysis, acidification, methanogenesis, interspecific H2 transfer, and urea cycling in ruminal metabolism are also discussed. Finally, we review the research progress on the conversion of biomass waste into biofuels (bioethanol, biohydrogen, and biomethane) and value-added chemicals (organic acids) by ruminal microbes. This review aims to provide new ideas and methods for ruminal microbe and enzyme applications, biomass waste conversion, and global energy shortage alleviation.

Gut diazotrophs in lagomorphs are associated with season but not altitude and host phylogeny

Invertebrates such as termites feeding on nutrient-poor substrate receive essential nitrogen by biological nitrogen fixation of gut diazotrophs. However, the diversity and composition of gut diazotrophs of vertebrates such as Plateau pikas living in nutrient-poor Qinghai-Tibet Plateau remain unknown. To fill this knowledge gap, we studied gut diazotrophs of Plateau pikas (Ochotona curzoniae) and its related species, Daurian pikas (Ochotona daurica), Hares (Lepus europaeus) and Rabbits (Oryctolagus cuniculus) by high-throughput amplicon sequencing methods. We analyzed whether the gut diazotrophs of Plateau pikas are affected by season, altitude, and species, and explored the relationship between gut diazotrophs and whole gut microbiomes. Our study showed that Firmicutes, Spirochaetes, and Euryarchaeota were the dominant gut diazotrophs of Plateau pikas. The beta diversity of gut diazotrophs of Plateau pikas was significantly different from the other three lagomorphs, but the alpha diversity did not show a significant difference among the four lagomorphs. The gut diazotrophs of Plateau pikas were the most similarly to that of Rabbits, followed by Daurian pikas and Hares, which was inconsistent with gut microbiomes or animal phylogeny. The dominant gut diazotrophs of the four lagomorphs may reflect their living environment and dietary habits. Season significantly affected the alpha diversity and abundance of dominant gut diazotrophs. Altitude had no significant effect on the gut diazotrophs of Plateau pikas. In addition, the congruence between gut microbiomes and gut diazotrophs was low. Our results proved that the gut of Plateau pikas was rich in gut diazotrophs, which is of great significance for the study of ecology and evolution of lagomorphs.

The energy metabolism of Balantidium polyvacuolum inhabiting the hindgut of Xenocypris davidi

Anaerobic parasitic ciliates are a specialized group of ciliates that are adapted to anoxic and oxygen-depleted habitats. Among them, Balantidium polyvacuolum, which inhabits the hindgut of Xenocyprinae fishes, has received very limited scientific attention, so the molecular mechanism of its adaptation to the digestive tract microenvironment is still unclear. In this study, transmission electron microscopy (TEM) and single-cell transcriptome analysis were used to uncover the metabolism of B. polyvacuolum. Starch granules, endosymbiotic bacteria, and multiple specialized mitochondrion-related organelles (MROs) of various shapes were observed. The MROs may have completely lost the electron transport chain (ETC) complexes I, III, IV, and V and only retained succinate dehydrogenase subunit A (SDHA) of complex II. The tricarboxylic acid (TCA) cycle was also incomplete. It can be inferred that the hypoxic intestinal environment has led to the specialization of the mitochondria in B. polyvacuolum. Moreover, carbohydrate-active enzymes (CAZymes), including carbohydrate esterases, enzymes with a carbohydrate-binding module, glycoside hydrolases, and glycosyltransferases, were identified, which may constitute evidence that B. polyvacuolum is able to digest carbohydrates and starch. These findings can improve our knowledge of the energy metabolism and adaptive mechanisms of B. polyvacuolum.

"Get the best out of what comes in" - adaptation of the microbiota of chamois (Rupicapra rupicapra) to seasonal forage availability in the Bavarian Alps

As an inhabitant of the Alps, chamois are exposed to significant climatic changes throughout the year and are also strongly confronted with changing forage availability. Besides horizontal and vertical migratory movements as an adaptation, it undergoes physiological transformations and dynamic changes in the ruminal microbiota. The following study used 48 chamois of different ages and genders to investigate to which extent the ingested food plants, the resulting crude nutrients in the rumen (reticulorumen) contents, and the bacterial microbiota in the rumen and their fermentation products were influenced by the changes over the seasons. Very little is known about the microbiota of wild ruminants, and many bacterial taxa could only be determined to certain taxonomic levels in this study. However, adapted microbiota reflects the significant changes in the ingested forage and the resulting crude nutrients. For some taxa, our results indicated potential functional relationships. In addition, 15 genera were identified, representing almost 90% of the relative abundance, forming the central part of the microbial community throughout the year. The successful and flexible adaptation of chamois is reflected in the chamois rumen's nutrient and microbial profile. This is also the first study that analyzes the microbiota of the chamois using rumen samples and considers the microbiota in a seasonal comparison.

The extent of nitrogen isotopic fractionation in rumen bacteria is associated with changes in rumen nitrogen metabolism

Nitrogen use efficiency is an important index in ruminants and can be indirectly evaluated through the N isotopic discrimination between the animal and its diet (Δ15Nanimal-diet). The concentration and source of N may determine both the extent of the N isotopic discrimination in bacteria and N use efficiency. We hypothesised that the uptake and release of ammonia by rumen bacteria will affect the natural 15N enrichment of the bacterial biomass over their substrates (Δ15Nbacteria-substrate) and thereby further impacting Δ15Nanimal-diet. To test this hypothesis, two independent in vitro experiments were conducted using two contrasting N sources (organic vs inorganic) at different levels either in pure rumen bacteria culture incubations (Experiment #1) or in mixed rumen cultures (Experiment #2). In Experiment #1, tryptone casein or ammonium chloride were tested at low (1 mM N) and high (11.5 mM N) concentrations on three rumen bacterial strains (Fibrobacter succinogenes, Eubacterium limosum and Xylanibacter ruminicola) incubated in triplicate in anaerobic batch monocultures during 48h. In Experiment #2 mixed rumen cultures were incubated during 120 h with peptone or ammonium chloride at five different levels of N (1.5, 3, 4.5, 6 and 12-mM). In experiment #1, Δ15Nbacteria-substrate was lowest when the ammonia-consumer bacterium Fibrobacter succinogenes was grown on ammonium chloride, and highest when the proteolytic bacterial strain Xylanibacter ruminicola was grown on tryptone. In experiment #2, Δ15Nbacteria-substrate was lower with inorganic (ammonium chloride) vs organic (peptone) N source. A strong negative correlation between Δ15Nbacteria-substrate and Rikenellaceae_RC9_gut_group, a potential fibrolytic rumen bacterium, was detected. Together, our results showed that Δ15Nbacteria-substrate may change according to the balance between synthesis of microbial protein from ammonia versus non-ammonia N sources and confirm the key role of rumen bacteria as modulators of Δ15Nanimal-diet.

Species-Level Taxonomic Characterization of Uncultured Core Gut Microbiota of Plateau Pika

Rarely has the vast diversity of bacteria on Earth been profiled, particularly on inaccessible plateaus. These uncultured microbes, which are also known as "microbial dark matter," may play crucial roles in maintaining the ecosystem and are linked to human health, regarding pathogenicity and prebioticity. The plateau pika (Ochotona curzoniae) is a small burrowing steppe lagomorph that is endemic to the Qinghai-Tibetan Plateau and is a keystone species in the maintenance of ecological balance. We used a combination of full-length 16S rRNA amplicon sequencing, shotgun metagenomics, and metabolomics to elucidate the species-level community structure and the metabolic potential of the gut microbiota of the plateau pika. Using a full-length 16S rRNA metataxonomic approach, we clustered 618 (166 ± 35 per sample) operational phylogenetic units (OPUs) from 105 plateau pika samples and assigned them to 215 known species, 226 potentially new species, and 177 higher hierarchical taxa. Notably, 39 abundant OPUs (over 60% total relative abundance) are found in over 90% of the samples, thereby representing a "core microbiota." They are all classified as novel microbial lineages, from the class to the species level. Using metagenomic reads, we independently assembled and binned 109 high-quality, species-level genome bins (SGBs). Then, a precise taxonomic assignment was performed to clarify the phylogenetic consistency of the SGBs and the 16S rRNA amplicons. Thus, the majority of the core microbes possess their genomes. SGBs belonging to the genus Treponema, the families Muribaculaceae, Lachnospiraceae, and Oscillospiraceae, and the order Eubacteriales are abundant in the metagenomic samples. In addition, multiple CAZymes are detected in these SGBs, indicating their efficient utilization of plant biomass. As the most widely connected metabolite with the core microbiota, tryptophan may relate to host environmental adaptation. Our investigation allows for a greater comprehension of the composition and functional capacity of the gut microbiota of the plateau pika. IMPORTANCE The great majority of microbial species remain uncultured, severely limiting their taxonomic characterization and biological understanding. The plateau pika (Ochotona curzoniae) is a small burrowing steppe lagomorph that is endemic to the Qinghai-Tibetan Plateau and is considered to be the keystone species in the maintenance of ecological stability. We comprehensively investigated the gut microbiota of the plateau pika via a multiomics endeavor. Combining full-length 16S rRNA metataxonomics, shotgun metagenomics, and metabolomics, we elucidated the species-level taxonomic assignment of the core uncultured intestinal microbiota of the plateau pika and revealed their correlation to host nutritional metabolism and adaptation. Our findings provide insights into the microbial diversity and biological significance of alpine animals.

Lignocellulose degradation by rumen bacterial communities: New insights from metagenome analyses

Ruminant animals house a dense and diverse community of microorganisms in their rumen, an enlarged compartment in their stomach, which provides a supportive environment for the storage and microbial fermentation of ingested feeds dominated by plant materials. The rumen microbiota has acquired diverse and functionally overlapped enzymes for the degradation of plant cell wall polysaccharides. In rumen Bacteroidetes, enzymes involved in degradation are clustered into polysaccharide utilization loci to facilitate coordinated expression when target polysaccharides are available. Firmicutes use free enzymes and cellulosomes to degrade the polysaccharides. Fibrobacters either aggregate lignocellulose-degrading enzymes on their cell surface or release them into the extracellular medium in membrane vesicles, a mechanism that has proven extremely effective in the breakdown of recalcitrant cellulose. Based on current metagenomic analyses, rumen Bacteroidetes and Firmicutes are categorized as generalist microbes that can degrade a wide range of polysaccharides, while other members adapted toward specific polysaccharides. Particularly, there is ample evidence that Verrucomicrobia and Spirochaetes have evolved enzyme systems for the breakdown of complex polysaccharides such as xyloglucans, peptidoglycans, and pectin. It is concluded that diversity in degradation mechanisms is required to ensure that every component in feeds is efficiently degraded, which is key to harvesting maximum energy by host animals.

Production, purification, characterization and application of two novel endoglucanases from buffalo rumen metagenome

BACKGROUND

Lignocellulose biomass is the most abundant and renewable material in nature. The objectives of this study were to characterize two endoglucanases TrepCel3 and TrepCel4, and determine the effect of the combination of them (1.2 mg TrepCel3, 0.8 mg TrepCel4) on in vitro rumen fermentation characteristics. In this study, three nature lignocellulosic substrates (rice straw, RS; wheat straw, WS; leymus chinensis, LC) were evaluated for their in vitro digestibility, gas, NH3-N and volatile fatty acid (VFA) production, and microbial protein (MCP) synthesis by adding enzymatic combination.

METHODS

Two endoglucanases' genes were successfully expressed in Escherichia coli (E. coli) BL21 (DE3), and enzymatic characteristics were further characterized. The combination of TrepCel3 and TrepCel4 was incubated with lignocellulosic substrates to evaluate its hydrolysis ability.

RESULTS

The maximum enzymatic activity of TrepCel3 was determined at pH 5.0 and 40 °C, while TrepCel4 was at pH 6.0 and 50 °C. They were stable over the temperature range of 30 to 60 °C, and active within the pH range of 4.0 to 9.0. The TrepCel3 and TrepCel4 had the highest activity in lichenan 436.9 ± 8.30 and 377.6 ± 6.80 U/mg, respectively. The combination of TrepCel3 and TrepCel4 exhibited the highest efficiency at the ratio of 60:40. Compared to maximum hydrolysis of TrepCel3 or TrepCel4 separately, this combination was shown to have a superior ability to maximize the saccharification yield from lignocellulosic substrates up to 188.4% for RS, 236.7% for wheat straw WS, 222.4% for LC and 131.1% for sugar beet pulp (SBP). Supplemental this combination enhanced the dry matter digestion (DMD), gas, NH3-N and VFA production, and MCP synthesis during in vitro rumen fermentation.

CONCLUSIONS

The TrepCel3 and TrepCel4 exhibited the synergistic relationship (60:40) and significantly increased the saccharification yield of lignocellulosic substrates. The combination of them stimulated in vitro rumen fermentation of lignocellulosic substrates. This combination has the potential to be a feed additive to improve agricultural residues utilization in ruminants. If possible, in the future, experiments in vivo should be carried out to fully evaluate its effect.

Dynamic changes in fecal microbiota in donkey foals during weaning: From pre-weaning to post-weaning

Introduction

A better understanding of the microbiota community in donkey foals during the weaning transition is a prerequisite to optimize gut function and improve feed efficiency. The objective of the present study was to investigate the dynamic changes in fecal microbiota in donkey foals from pre-to post-weaning period.

Methods

A total of 27 fecal samples of donkey foals were collected in the rectum before morning feeding at pre-weaning (30 days of age, PreW group, n = 9), dur-weaning (100 days of age, DurW group, n = 9) and post-weaning (170 days of age, PostW group, n = 9) period. The 16S rRNA amplicon sequencing were employed to indicate the microbial changes during the weaning period.

Results

In the present study, the cessation of breastfeeding gradually and weaning onto plant-based feeds increased the microbial diversity and richness, with a higher Shannon, Ace, Chao and Sobs index in DurW and PostW than in PreW (p < 0.05). The predominant bacterial phyla in donkey foal feces were Firmicutes (>50.5%) and Bacteroidota (>29.5%), and the predominant anaerobic fungi and archaea were Neocallimastigomycota and Euryarchaeota. The cellulolytic related bacteria including phylum Firmicutes, Spirochaetota and Fibrobacterota and genus norank_f_F082, Treponema, NK4A214_group, Lachnospiraceae_AC2044_group and Streptococcus were increased from pre-to post-weaning donkey foals (p < 0.05). Meanwhile, the functions related to the fatty acid biosynthesis, carbohydrate metabolism and amino acid biosynthesis were significantly enriched in the fecal microbiome in the DurW and PostW donkeys. Furthermore, the present study provided the first direct evidence that the initial colonization and establishment of anaerobic fungi and archaea in donkey foals began prior to weaning. The relative abundance of Orpinomyces were the highest in DurW donkey foals among the three groups (p < 0.01). In terms of archaea, the abundance of Methanobrevibacter were higher in PreW than in DurW and PostW (p < 0.01), but the abundance of Methanocorpusculum were significantly increased in DurW and PostW compared to PreW donkey foals (p < 0.01).

Discussion

Altogether, the current study contributes to a comprehensive understanding of the development of the microbiota community in donkey foals from pre-to post-weaning period, which may eventually result in an improvement of the digestion and feed efficiency in donkeys.

Effect of Methionine Hydroxy Analog on Hu Sheep Digestibility, Rumen Fermentation, and Rumen Microbial Community In Vitro

This experiment was conducted to evaluate the effects of a methionine hydroxy analog (MHA) on in vitro gas production, rumen fermentation parameters, and rumen microbiota. Two different MHA, 2-hydroxy-4-(methylthio) butanoic acid isopropyl ester (HMBi) and the calcium salt of the hydroxy analog of methionine (MHA-Ca), were selected for in vitro experiments. The treatments were the Control group (0% of MHA), HMBi group (2%HMBi), and MHA-Ca group (2%MHA-Ca). Dry matter digestibility was measured after 12 h and 24 h of fermentation, and fermentation parameters and microbial composition were analyzed after 24 h. HMBi and MHA-Ca showed increased (p = 0.001) cumulative gas production in 3 h. The total volatile fatty acids, microbial protein (MCP) concentration, acetate, and acetate to propionate ratio in the HMBi and MHA-Ca groups were significantly higher than those in the Control group (p = 0.006, p = 0.002, p = 0.001, p = 0.004), and the NH₃-N concentrations in the HMBi and MHA-Ca groups were significantly lower than those in the Control group (p = 0.004). The 16S rRNA sequencing revealed that the HMBi group had a higher (p = 0.039, p = 0.001, p = 0.027) relative abundance of Bacteroidetes, Firmicutes, and Synergistetes and a lower relative abundance of Proteobacteria (p = 0.001) than the Control group. At the genus level, Prevotella abundance was higher (p = 0.001), while Ruminobacter abundance was lower (p = 0.001), in the HMBi and MHA-Ca groups than in the Control group. Spearman's correlation analysis showed that the relative abundance of Prevotella_1, Streptococcus, and Desulfovibrio was positively correlated with dry matter digestibility, MCP, and fermentation parameters. MHA, thus, significantly increased gas production and altered the rumen fermentation parameters and microbiota composition of sheep.

The claim of primacy of human gut Bacteroides ovatus in dietary cellobiose degradation

A demonstration of cellulose degrading bacterium from human gut changed our view that human cannot degrade the cellulose. However, investigation of cellulose degradation by human gut microbiota on molecular level has not been completed so far. We showed here, using cellobiose as a model that promoted the growth of human gut key members, such as Bacteroides ovatus (BO), to clarify the molecular mechanism. Our results showed that a new polysaccharide utilization locus (PUL) from BO was involved in the cellobiose capturing and degradation. Further, two new cellulases BACOVA_02626GH5 and BACOVA_02630GH5 on the cell surface performed the degradation of cellobiose into glucose were determined. The predicted structures of BACOVA_02626GH5 and BACOVA_02630GH5 were highly homologous with the cellulase from soil bacteria, and the catalytic residues were highly conservative with two glutamate residues. In murine experiment, we observed cellobiose reshaped the composition of gut microbiota and probably modified the metabolic function of bacteria. Taken together, our findings further highlight the evidence of cellulose can be degraded by human gut microbes and provide new insight in the field of investigation on cellulose.

Prevotella: A Key Player in Ruminal Metabolism

Ruminants are foregut fermenters that have the remarkable ability of converting plant polymers that are indigestible to humans into assimilable comestibles like meat and milk, which are cornerstones of human nutrition. Ruminants establish a symbiotic relationship with their microbiome, and the latter is the workhorse of carbohydrate fermentation. On the other hand, during carbohydrate fermentation, synthesis of propionate sequesters H, thus reducing its availability for the ultimate production of methane (CH4) by methanogenic archaea. Biochemically, methane is the simplest alkane and represents a downturn in energetic efficiency in ruminants; environmentally, it constitutes a potent greenhouse gas that negatively affects climate change. Prevotella is a very versatile microbe capable of processing a wide range of proteins and polysaccharides, and one of its fermentation products is propionate, a trait that appears conspicuous in P. ruminicola strain 23. Since propionate, but not acetate or butyrate, constitutes an H sink, propionate-producing microbes have the potential to reduce methane production. Accordingly, numerous studies suggest that members of the genus Prevotella have the ability to divert the hydrogen flow in glycolysis away from methanogenesis and in favor of propionic acid production. Intended for a broad audience in microbiology, our review summarizes the biochemistry of carbohydrate fermentation and subsequently discusses the evidence supporting the essential role of Prevotella in lignocellulose processing and its association with reduced methane emissions. We hope this article will serve as an introduction to novice Prevotella researchers and as an update to others more conversant with the topic.

Exploration of rumen microbial and carbohydrate-active enzyme profiles in cattle fed coir a lignin-rich diet using a metagenomic approach

Lignocellulosic biomass is a rich source of feed for cattle. Amongst them, coconut coir may be the potential source of feed supplements. To assess, the effect of various concentrations of coconut coir (0 %, 21 % and 40 %) as a feed supplement on the rumen microbiome of cattle (Kankrej breed), a metagenomic (16S rRNA gene amplicon and shotgun sequencing) study was performed. The Alpha diversity estimation from the amplicon study suggested that the group of cattle fed food without the coconut coir has a higher number of genera than the cattle fed with mixed ration. Within the liquid fraction, bacterial phyla Bacteroidetes were abundant followed by Firmicutes and Fibrobacteres, whereas the proportion of Tenericutes, TM7, SRI, Verrucomicrobia, Lentisphaerae, and Elusimicrobia had decreased with the rise in the coir concentration. While within the solid fractions, the proportion of Elusimicrobia increased, but the count of Bacteriodetes, Firmicutes, Fibrobacteres Tenericutes, TM7, SRI, Verrucomicrobia, and Lentisphaerae decreased with an increase in coir percentages. The results obtained from shotgun sequencing show similar results for bacterial diversity. The functions associated with carbohydrate metabolism were abundant in both the treatments as compared to the control. Functions related to glycoside hydrolases, glycosyltransferases and carbohydrate-binding modules were abundant in both the treatments as compared to control. Thus, the study indicates that the microbiome does alter after feeding coir as a supplement and may be used as feed for cattle.

Microbiota-host crosstalk in the newborn and adult rumen at single-cell resolution

BACKGROUND

The rumen is the hallmark organ of ruminants, playing a vital role in their nutrition and providing products for humans. In newborn suckling ruminants milk bypasses the rumen, while in adults this first chamber of the forestomach has developed to become the principal site of microbial fermentation of plant fibers. With the advent of single-cell transcriptomics, it is now possible to study the underlying cell composition of rumen tissues and investigate how this relates the development of mutualistic symbiosis between the rumen and its epithelium-attached microbes.

RESULTS

We constructed a comprehensive cell landscape of the rumen epithelium, based on single-cell RNA sequencing of 49,689 high-quality single cells from newborn and adult rumen tissues. Our single-cell analysis identified six immune cell subtypes and seventeen non-immune cell subtypes of the rumen. On performing cross-species analysis of orthologous genes expressed in epithelial cells of cattle rumen and the human stomach and skin, we observed that the species difference overrides any cross-species cell-type similarity. Comparing adult with newborn cattle samples, we found fewer epithelial cell subtypes and more abundant immune cells, dominated by T helper type 17 cells in the rumen tissue of adult cattle. In newborns, there were more fibroblasts and myofibroblasts, an IGFBP3+ epithelial cell subtype not seen in adults, while dendritic cells were the most prevalent immune cell subtype. Metabolism-related functions and the oxidation-reduction process were significantly upregulated in adult rumen epithelial cells. Using 16S rDNA sequencing, fluorescence in situ hybridization, and absolute quantitative real-time PCR, we found that epithelial Desulfovibrio was significantly enriched in the adult cattle. Integrating the microbiome and metabolome analysis of rumen tissues revealed a high co-occurrence probability of Desulfovibrio with pyridoxal in the adult cattle compared with newborn ones while the scRNA-seq data indicated a stronger ability of pyroxidal binding in the adult rumen epithelial cell subtypes. These findings indicate that Desulfovibrio and pyridoxal likely play important roles in maintaining redox balance in the adult rumen.

CONCLUSIONS

Our integrated multi-omics analysis provides novel insights into rumen development and function and may facilitate the future precision improvement of rumen function and milk/meat production in cattle.

Sex Differences in Fecal Microbiome Composition and Function of Dromedary Camels in Saudi Arabia

The gastrointestinal microbiome plays a significant role in diet digestion and the energy production of its host. Several factors that affect the gastrointestinal microbiota composition were studied in camels. Yet, the impact of sex on the gastrointestinal bacteriome of camels remains unexplored to date. In this perspective, the fecal microbiome community composition from dromedary camels was determined in 10 male and 10 female samples using the 16S rRNA amplicon, in order to estimate if this was influenced by sex. The core microbiome in females contained 284 bacterial OTUs and one archaeal OUT, whereas in males, it contained 279 bacterial OTUs and one archaeal OTU. In females, Bacteroidetes and Spirochaetes were significantly more abundant than in male camels, whereas Lentisphaerae and Euryarchaeota were significantly abundant in males. According to Principal Coordinate Analysis and UPGMA clustering, grouping with respect to sex was observed. The functional prediction results showed differences such as energy production and conversion, and that the cell wall/membrane/envelope were enriched in female camels. The fecal microbiome of male camels was rich in amino acid, lipid transport and metabolism.

Investigating the impact of database choice on the accuracy of metagenomic read classification for the rumen microbiome

Microbiome analysis is quickly moving towards high-throughput methods such as metagenomic sequencing. Accurate taxonomic classification of metagenomic data relies on reference sequence databases, and their associated taxonomy. However, for understudied environments such as the rumen microbiome many sequences will be derived from novel or uncultured microbes that are not present in reference databases. As a result, taxonomic classification of metagenomic data from understudied environments may be inaccurate. To assess the accuracy of taxonomic read classification, this study classified metagenomic data that had been simulated from cultured rumen microbial genomes from the Hungate collection. To assess the impact of reference databases on the accuracy of taxonomic classification, the data was classified with Kraken 2 using several reference databases. We found that the choice and composition of reference database significantly impacted on taxonomic classification results, and accuracy. In particular, NCBI RefSeq proved to be a poor choice of database. Our results indicate that inaccurate read classification is likely to be a significant problem, affecting all studies that use insufficient reference databases. We observed that adding cultured reference genomes from the rumen to the reference database greatly improved classification rate and accuracy. We also demonstrated that metagenome-assembled genomes (MAGs) have the potential to further enhance classification accuracy by representing uncultivated microbes, sequences of which would otherwise be unclassified or incorrectly classified. However, classification accuracy was strongly dependent on the taxonomic labels assigned to these MAGs. We therefore highlight the importance of accurate reference taxonomic information and suggest that, with formal taxonomic lineages, MAGs have the potential to improve classification rate and accuracy, particularly in environments such as the rumen that are understudied or contain many novel genomes.

Metagenomic Analysis of in Vitro Ruminal Fermentation Reveals the Role of the Copresent Microbiome in Plant Biomass Degradation

In vitro ruminal fermentation is considered an efficient way to degrade crop residue. To better understand the microbial communities and their functions during in vitro ruminal fermentation, the microbiome and short chain fatty acid (SCFA) production were investigated using the metagenomic sequencing and rumen simulation technique (RUSITEC) system. A total of 1677 metagenome-assembled genomes (MAGs) were reconstructed, and 298 MAGs were found copresenting in metagenomic data of the current work and 58 previously ruminal representative samples. Additionally, the domains related to pectin and xylan degradation were overrepresented in the copresent MAGs compared with total MAGs. Among the copresent MAGs, we obtained 14 MAGs with SCFA-synthesis-related genes positively correlated with SCFA concentrations. The MAGs obtained from this study enable a better understanding of dominant microbial communities across in vivo and in vitro ruminal fermentation and show promise for pointing out directions for further research on in vitro ruminal fermentation.

Rumen Metaproteomics Highlight the Unique Contributions of Microbe-Derived Extracellular and Intracellular Proteins for In Vitro Ruminal Fermentation

Rumen microorganisms can be used in in vitro anaerobic fermentation to encourage the sustainable exploitation of agricultural wastes. However, the understanding of active microbiota under in vitro ruminal fermentation conditions is still insufficient. To investigate how rumen microbes actively participate in the fermentation process in vitro, we resolved the metaproteome generated from ruminal fermentation broth after seven days of in vitro incubation. Herein, the sample-specific database for metaproteomic analysis was constructed according to the metagenomic data of in vitro ruminal fermentation. Based on the sample-specific database, we found in the metaproteome that Bacteroidetes and Firmicutes_A were the most active in protein expression, and over 50% of these proteins were assigned to gene categories involved in energy conversion and basic structures. On the other hand, a variety of bacteria-derived extracellular proteins, which contained carbohydrate-active enzyme domains, were found in the extracellular proteome of fermentation broth. Additionally, the bacterial intracellular/surface moonlighting proteins (ISMPs) and proteins of outer membrane vesicles were detected in the extracellular proteome, and these ISMPs were involved in maintaining microbial population size through potential adherence to substrates. The metaproteomic characterizations of microbial intracellular/extracellular proteins provide new insights into the ability of the rumen microbiome to maintain in vitro ruminal fermentation.

Comparative and functional analyses of fecal microbiome in Asian elephants

Asian elephant is large herbivorous animal with elongated hindgut. To explore fecal microbial community composition with various ages, sex and diets, and their role in plant biomass degrading and nutrition conversation. We generated 119 Gb by metagenome sequencing from 10 different individual feces and identified 5.3 million non-redundant genes. The comprehensive analysis established that the Bacteroidetes, Firmicutes and Proteobacteria constituted the most dominant phyla in overall fecal samples. In different individuals, the alpha diversity of the fecal microbiota in female was lower than male, and the alpha diversity of the fecal microbiota in older was higher than younger, and the fecal microbial diversity was the most complex in wild elephant. But the predominant population compositions were similar to each other. Moreover, the newborn infant elephant feces assembled and maintained a diverse but host-specific fecal microbial population. The discovery speculated that Asian elephant maybe have start to building microbial populations before birth. Meanwhile, these results illustrated that host phylogeny, diets, ages and sex are significant factors for fecal microbial community composition. Therefore, we put forward the process of Asian elephant fecal microbial community composition that the dominant populations were built first under the guidance of phylogeny, and then shaped gradually a unique and flexible gut microbial community structure under the influences of diet, age and sex. This study found also that the Bacteroidetes were presumably the main drivers of plant fiber-degradation. A large of secondary metabolite biosynthetic gene clusters, and genes related to enediyne biosynthesis were found and showed that the Asian elephant fecal microbiome harbored a diverse and abundant genetic resource. A picture of antibiotic resistance genes (ARGs) reservoirs of fecal microbiota in Asian elephants was provided. Surprisingly, there was such wide range of ARGs in newborn infant elephant. Further strengthening our speculation that the fetus of Asian elephant has colonized prototypical fecal microbiota before birth. However, it is necessary to point out that the data give a first inside into the gut microbiota of Asian elephants but too few individuals were studied to draw general conclusions for differences among wild and captured elephants, female and male or different ages. Further studies are required. Additionally, the cultured actinomycetes from Asian elephant feces also were investigated, which the feces of Asian elephants could be an important source of actinomycetes.

Metagenomic insights into the microbe-mediated B and K2 vitamin biosynthesis in the gastrointestinal microbiome of ruminants

BACKGROUND

B and K₂ vitamins, essential nutrients in host metabolism, can be synthesized by the rumen microbiome in ruminants and subsequently absorbed by the host. However, the B and K₂ vitamin biosynthesis by the whole gastrointestinal microbiome and their abundances in different dietary strategies are largely unknown. Here, we reanalyzed our previous large-scale metagenomic data on the gastrointestinal microbiome of seven ruminant species and recruited 17,425 nonredundant microbial genomes from published datasets to gain a comprehensive understanding of the microbe-mediated B and K₂ vitamin biosynthesis in ruminants.

RESULTS

We identified 1,135,807 genes and 167 enzymes involved in B and K₂ vitamin biosynthesis. Our results indicated that the total abundances of B and K₂ vitamin biosynthesis were dominant in the stomach microbiome, while the biosynthesis of thiamine, niacin, and pyridoxine was more abundant in the large intestine. By examining 17,425 nonredundant genomes, we identified 2366 high-quality genomes that were predicted to de novo biosynthesize at least one vitamin. Genomic analysis suggested that only 2.7% of these genomes can synthesize five or more vitamins, and nearly half of genomes can synthesize only one vitamin. Moreover, we found that most genomes possessed cobalamin transporters or cobalamin-dependent enzymes to consume cobalamin directly, and only a few microbial genomes possessed a complete cobalamin biosynthesis pathway. Based on these genomic data, we examined the effect of the high-grain (HG) diet on the vitamin biosynthesis of the rumen microbiome of dairy cattle. We revealed that most vitamin biosynthesis was enhanced in the HG group, while only cobalamin synthesis was inhibited in the HG group, indicating that dietary fiber is vital for cobalamin biosynthesis.

CONCLUSIONS

We primarily provided a gene catalog and 2366 microbial genomes involved in B and K₂ vitamin biosynthesis in ruminants. Our findings demonstrated the regional heterogeneity and dietary effect of vitamin biosynthetic potential in the ruminant gastrointestinal microbiome and interpreted the biosynthesis mechanisms of these microbes and their physiological adaptability. This study expands our understanding of microbe-mediated vitamin biosynthesis in ruminants and may provide novel targets for manipulation to improve the production of these essential vitamins. Video abstract.

Metaproteomics reveals enzymatic strategies deployed by anaerobic microbiomes to maintain lignocellulose deconstruction at high solids

Economically viable production of cellulosic biofuels requires operation at high solids loadings—on the order of 15 wt%. To this end we characterize Nature’s ability to deconstruct and utilize mid-season switchgrass at increasing solid loadings using an anaerobic methanogenic microbiome. This community exhibits undiminished fractional carbohydrate solubilization at loadings ranging from 30 g/L to 150 g/L. Metaproteomic interrogation reveals marked increases in the abundance of specific carbohydrate-active enzyme classes. Significant enrichment of auxiliary activity family 6 enzymes at higher solids suggests a role for Fenton chemistry. Stress-response proteins accompanying these reactions are similarly upregulated at higher solids, as are β-glucosidases, xylosidases, carbohydrate-debranching, and pectin-acting enzymes—all of which indicate that removal of deconstruction inhibitors is important for observed undiminished solubilization. Our work provides insights into the mechanisms by which natural microbiomes effectively deconstruct and utilize lignocellulose at high solids loadings, informing the future development of defined cultures for efficient bioconversion.

Fecal microbiome of horses transitioning between warm-season and cool-season grass pasture within integrated rotational grazing systems

BACKGROUND

Diet is a key driver of equine hindgut microbial community structure and composition. The aim of this study was to characterize shifts in the fecal microbiota of grazing horses during transitions between forage types within integrated warm- (WSG) and cool-season grass (CSG) rotational grazing systems (IRS). Eight mares were randomly assigned to two IRS containing mixed cool-season grass and one of two warm-season grasses: bermudagrass [Cynodon dactylon (L.) Pers.] or crabgrass [Digitaria sanguinalis (L.) Scop.]. Fecal samples were collected during transitions from CSG to WSG pasture sections (C-W) and WSG to CSG (W-C) on days 0, 2, 4, and 6 following pasture rotation and compared using 16S rRNA gene sequencing.

RESULTS

Regardless of IRS or transition (C-W vs. W-C), species richness was greater on day 4 and 6 in comparison to day 0 (P < 0.05). Evenness, however, did not differ by day. Weighted UniFrac also did not differ by day, and the most influential factor impacting β-diversity was the individual horse (R² ≥ 0.24; P = 0.0001). Random forest modeling was unable to accurately predict days within C-W and W-C, but could predict the individual horse based on microbial composition (accuracy: 0.92 ± 0.05). Only three differentially abundant bacterial co-abundance groups (BCG) were identified across days within all C-W and W-C for both IRS (W ≥ 126). The BCG differing by day for all transitions included amplicon sequence variants (ASV) assigned to bacterial groups with known fibrolytic and butyrate-producing functions including members of Lachnospiraceae, Clostridium sensu stricto 1, Anaerovorax the NK4A214 group of Oscillospiraceae, and Sarcina maxima. In comparison, 38 BCG were identified as differentially abundant by horse (W ≥ 704). The ASV in these groups were most commonly assigned to genera associated with degradation of structural carbohydrates included Rikenellaceae RC9 gut group, Treponema, Christensenellaceae R-7 group, and the NK4A214 group of Oscillospiraceae. Fecal pH also did not differ by day.

CONCLUSIONS

Overall, these results demonstrated a strong influence of individual horse on the fecal microbial community, particularly on the specific composition of fiber-degraders. The equine fecal microbiota were largely stable across transitions between forages within IRS suggesting that the equine gut microbiota adjusted at the individual level to the subtle dietary changes imposed by these transitions. This adaptive capacity indicates that horses can be managed in IRS without inducing gastrointestinal dysfunction.

Unique pool of carbohydrate-degrading enzymes in novel bacteria assembled from cow and buffalo rumen metagenomes

Reconstruction of genomes from environmental metagenomes offers an excellent prospect for studying the metabolic potential of organisms resilient to isolation in laboratory conditions. Here, we assembled 12 high-quality metagenome-assembled genomes (MAGs) with an estimated completion of ≥ 90% from cow and buffalo rumen metagenomes. Average nucleotide identity (ANI) score-based screening with an existing database suggests the novelty of these genomes. Gene prediction led to the identification of 30,359 protein-encoding genes (PEGs) across 12 genomes, of which only 44.8% were annotated against a specific functional attribute. Further analysis revealed the presence of 985 carbohydrate-active enzymes (CAZymes) from more than 50 glycoside hydrolase families, of which 90% do not have a proper match in the CAZy database. Genome mining revealed the presence of a high frequency of plant biomass deconstructing genes in Bacteroidetes MAGs compared to Firmicutes. The results strongly indicate that the rumen chamber harbors high numbers of deeply branched and as-yet uncultured microbes that encode novel CAZymes, candidates for prospective usage in plant biomass-hydrolyzing and biofuels industries. KEY POINTS: • Genome binning plays a crucial role in revealing the metabolic potential of uncultivable microbes. • Assembled 12 novel genomes from cow and buffalo rumen metagenome datasets. • High frequency of plant biomass deconstructing genes identified in Bacteroidetes MAGs.

Lignocellulose degradation in Protaetia brevitarsis larvae digestive tract: refining on a tightly designed microbial fermentation production line

BACKGROUND

The Scarabaeidae insect Protaetia brevitarsis (PB) has recently gained increasing research interest as a resource insect because its larvae can effectively convert decaying organic matter to plant growth-promoting frass with a high humic acid content and produce healthy, nutritional insect protein sources. Lignocellulose is the main component of PB larvae (PBL) feed, but PB genome annotation shows that PBL carbohydrate-active enzymes are not able to complete the lignocellulose degradation process. Thus, the mechanism by which PBL efficiently degrade lignocellulose is worthy of further study.

RESULTS

Herein, we used combined host genomic and gut metagenomic datasets to investigate the lignocellulose degradation activity of PBL, and a comprehensive reference catalog of gut microbial genes and host gut transcriptomic genes was first established. We characterized a gene repertoire comprising highly abundant and diversified lignocellulose-degrading enzymes and demonstrated that there was unique teamwork between PBL and their gut bacterial microbiota for efficient lignocellulose degradation. PBL selectively enriched lignocellulose-degrading microbial species, mainly from Firmicutes and Bacteroidetes, which are capable of producing a broad array of cellulases and hemicellulases, thus playing a major role in lignocellulosic biomass degradation. In addition, most of the lignocellulose degradation-related module sequences in the PBL microbiome were novel. PBL provide organic functional complementarity for lignocellulose degradation via their evolved strong mouthparts, alkaline midgut, and mild stable hindgut microenvironment to facilitate lignocellulosic biomass grinding, dissolving, and symbiotic microbial fermentation, respectively.

CONCLUSIONS

This work shows that PBL are a promising model to study lignocellulose degradation, which can provide highly abundant novel enzymes and relevant lignocellulose-degrading bacterial strains for biotechnological biomass conversion industries. The unique teamwork between PBL and their gut symbiotic bacterial microbiota for efficient lignocellulose degradation will expand the knowledge of holobionts and open a new beginning in the theory of holobionts. Video Abstract.

Microbial Identification Using rRNA Operon Region: Database and Tool for Metataxonomics with Long-Read Sequence

Recent development of long-read sequencing platforms has enabled researchers to explore bacterial community structure through analysis of full-length 16S rRNA gene (∼1,500 bp) or 16S-ITS-23S rRNA operon region (∼4,300 bp), resulting in higher taxonomic resolution than short-read sequencing platforms. Despite the potential of long-read sequencing in metagenomics, resources and protocols for this technology are scarce. Here, we describe MIrROR, the database and analysis tool for metataxonomics using the bacterial 16S-ITS-23S rRNA operon region. We collected 16S-ITS-23S rRNA operon sequences extracted from bacterial genomes from NCBI GenBank and performed curation. A total of 97,781 16S-ITS-23S rRNA operon sequences covering 9,485 species from 43,653 genomes were obtained. For user convenience, we provide an analysis tool based on a mapping strategy that can be used for taxonomic profiling with MIrROR database. To benchmark MIrROR, we compared performance against publicly available databases and tool with mock communities and simulated data sets. Our platform showed promising results in terms of the number of species covered and the accuracy of classification. To encourage active 16S-ITS-23S rRNA operon analysis in the field, BLAST function and taxonomic profiling results with 16S-ITS-23S rRNA operon studies, which have been reported as BioProject on NCBI are provided. MIrROR (http://mirror.egnome.co.kr/) will be a useful platform for researchers who want to perform high-resolution metagenome analysis with a cost-effective sequencer such as MinION from Oxford Nanopore Technologies. IMPORTANCE Metabarcoding is a powerful tool to investigate community diversity in an economic and efficient way by amplifying a specific gene marker region. With the advancement of long-read sequencing technologies, the field of metabarcoding has entered a new phase. The technologies have brought a need for development in several areas, including new markers that long-read can cover, database for the markers, tools that reflect long-read characteristics, and compatibility with downstream analysis tools. By constructing MIrROR, we met the need for a database and tools for the 16S-ITS-23S rRNA operon region, which has recently been shown to have sufficient resolution at the species level. Bacterial community analysis using the 16S-ITS-23S rRNA operon region with MIrROR will provide new insights from various research fields.

Metagenomics Reveals the Diversity and Taxonomy of Carbohydrate-Active Enzymes and Antibiotic Resistance Genes in Suancai Bacterial Communities

Suancai, as a traditional fermented food in China with reputed health benefits, has piqued global attention for many years. In some circumstances, the microbial-driven fermentation may confer health (e.g., probiotics) or harm (e.g., antibiotic resistance genes) to the consumers. To better utilize beneficial traits, a deeper comprehension of the composition and functionality of the bacterial species harboring enzymes of catalytically active is required. On the other hand, ingestion of fermented food increases the likelihood of microbial antibiotic resistance genes (ARGs) spreading in the human gastrointestinal tract. Besides, the diversity and taxonomic origin of ARGs in suancai are little known. In our study, a metagenomic approach was employed to investigate distribution structures of CAZymes and ARGs in main bacterial species in suancai. Functional annotation using the CAZy database identified a total of 8796 CAZymes in metagenomic data. A total of 83 ARGs were detected against the CARD database. The most predominant ARG category is multidrug-resistant genes. The ARGs of antibiotic efflux mechanism are mostly in Proteobacteria. The resistance mechanism of ARGs in Firmicutes is primarily antibiotic inactivation, followed by antibiotic efflux. Due to the abundance of species with different ARGs, strict quality control including microbial species, particularly those with lots of ARGs, is vital for decreasing the risk of ARG absorption via consumption. Ultimately, we significantly widen the understanding of suancai microbiomes by using metagenomic sequencing to offer comprehensive information on the microbial functional potential (including CAZymes and ARGs content) of household suancai.

The mechanism by which Enteromorpha Linza polysaccharide promotes Bacillus subtilis growth and nitrate removal

In this study, we discussed the relationship between Entermorpha linza polysaccharide (EP) and Bacillus subtilis, which can transform nitrate. A sole carbon source experiment showed that Bacillus subtilis could utilize EP, and the bacterial density was maximally increased by 54.43% in the EP groups. The results of reducing sugar determination proved the secretion of polysaccharide-degrading enzymes. Scanning electron microscopy (SEM) showed that the EP groups had fewer spores and shrunken bacteria, indicating that EP could improve the growth environment and maintain bacterial integrity. Additionally, the ratios of periplasmic nitrate reductase (NAP), nitrite reductase (NIR), and dissimilatory nitrate reductase (D-NRase) in the EP groups were maximally increased by 107.22%, 84.70% and 36.10%, respectively. Transcriptome analysis further confirmed the above mentioned results. For example, the high expression of quorum sensing genes indicated that EP groups had higher bacterial density. Moreover, the high expression of antioxidant genes in the EP groups may be related to morphological integrity. Our study provides a basis for further discussion of the mechanism.

The effect of droplet size on syntrophic dynamics in droplet-enabled microbial co-cultivation

Co-cultivation in microfluidic droplets has emerged as a versatile tool for the study of natural and synthetic microbial communities. In particular, the identification and characterization of syntrophic interactions in these communities is attracting increasing interest due to their critical importance for the functioning of environmental and host-associated communities as well as new biotechnological applications. However, one critical parameter in droplet-enabled co-cultivation that has evaded appropriate evaluation is the droplet size. Given the same number of initial cells, a larger droplet size can increase the length scale secreted metabolites must diffuse as well as dilute the initial concentration of cells and exchanged metabolites, impacting the community dynamics. To evaluate the effect of droplet size on a spectrum of syntrophic interactions, we cultivated a synthetic model system consisting of two E. coli auxotrophs, whose interactions could be modulated through supplementation of related amino acids in the medium. Our results demonstrate that the droplet size impacts substantially numerous aspects of the growth of a cross-feeding bi-culture, particularly the growth capacity, maximum specific growth rate, and lag time, depending on the degree of the interaction. This work heavily suggests that one droplet size does not fit all types of interactions; this parameter should be carefully evaluated and chosen in experimental studies that aim to utilize droplet-enabled co-cultivation to characterize or elucidate microbial interactions.

Reliable and Scalable Identification and Prioritization of Putative Cellulolytic Anaerobes With Large Genome Data

In the era of high-throughput sequencing, genetic information that is inherently whispering hints of the microbes’ functional niches is becoming easily accessible; however, properly identifying and characterizing these genetic hints to infer the microbes’ functional niches remains a challenge. Regarding genome-centric interpretation on the specific functional niche of cellulose hydrolysis for anaerobes, often encountered in practice is a lack of confidence in predicting the anaerobes’ real cellulolytic competency based solely on abundances of the varying carbohydrate-active enzyme modules annotated or on their taxonomy affiliation. Recognition of the synergy machineries that include but not limited to the cellulosome gene clusters is equally important as the annotation of individual carbohydrate-active modules or genes. In the interpretation of complete genomes of 2,768 microbe strains whose phenotypes have been well documented, with the incorporation of an automatic recognition of synergy among the carbohydrate active elements annotated, an explicit genotype–phenotype correlation was evidenced to be feasible for cellulolytic anaerobes, and a bioinformatic pipeline was developed accordingly. This genome-centric pipeline would categorize putative cellulolytic anaerobes into six genotype groups based on differential cellulose-hydrolyzing capacity and varying synergy mechanisms. Suggested in this genotype–phenotype correlation analysis was a finer categorization of the cellulosome gene clusters: although cellulosome complexes, by their nature, could enable the assembly of a number of carbohydrate-active units, they do not certainly guarantee the formation of the cellulose–enzyme–microbe complex or the cellulose-hydrolyzing activity of the corresponding anaerobe strains, for example, the well-known Clostridium acetobutylicum strains. Also, recognized in this genotype-phenotype correlation analysis was the genetic foundation of a previously unrecognized machinery that may mediate the microbe–cellulose adhesion, to be specific, enzymes encoded by genes harboring both the surface layer homology and cellulose-binding CBM modules. Applicability of this pipeline on scalable annotation of large genome datasets was further tested with the annotation of 7,902 reference genomes downloaded from NCBI, from which 14 genomes of putative paradigm cellulose-hydrolyzing anaerobes were identified. We believe the pipeline developed in this study would be a good add as a bioinformatic tool for genome-centric interpretation of uncultivated anaerobes, specifically on their functional niche of cellulose hydrolysis.

Metagenomic Analysis Reveals New Microbiota Related to Fiber Digestion in Pigs

Making full use of high fiber and low-cost crop coproducts is helpful to alleviate the situation of people and livestock competing for crops. Digestion of dietary fibers in pigs is mainly through microbial fermentation in the large intestine. To reveal microbiota related to fiber digestion in pigs, fecal samples have been collected from 274 healthy female Suhuai pigs at 160 days of age under the same feeding conditions and have measured apparent neutral detergent fiber (NDF) and acid detergent fiber (ADF) digestibility. Samples from Suhuai pigs with extreme high and low apparent NDF digestibility and extreme high and low apparent ADF digestibility were subjected to shotgun metagenomic sequencing. At the species level, 62 microbial species in H_NDF group and 54 microbial species in H_ADF group were related to high fiber digestibility. Among them, Lachnospiraceae bacterium 3-1 and Alistipes sp. CAG:514 may be new types of microorganisms associated with fiber digestion. In addition, we found that more abundant GH5 and GH48 family (contribute to cellulose degradation) genes, GH39 and GH53 family (contribute to hemicellulose degradation) genes in microorganisms may contribute to the higher apparent NDF digestibility of pigs, and more abundant GH3 and GH9 family (contribute to cellulose degradation) genes in microorganisms may contribute to the higher apparent ADF digestibility of pigs. The abundance of AA4 family (helps in lignin degradation) genes in H_NDF and H_ADF groups was significantly higher than that in L_NDF and L_ADF groups, respectively (P < 0.05). Three pathways in H_NDF group and four pathways in H_ADF group are important pathways associated with degradation of non-starch polysaccharides, and their relative abundance is significantly higher than that in L_NDF and L_ADF groups, respectively. Gut microbiota of Suhuai pigs with high apparent fiber digestibility had higher abundance of genes and microbiota related to fiber digestion and may have stronger fiber digestion potential compared with low apparent fiber digestibility group. This study revealed that the characteristics of gut microbiota and microbial gene functions of pigs with high fiber apparent digestibility, which provided a theoretical basis and reference for further understanding the impact of gut microbiota on fiber digestibility of pigs.

Accessing Dietary Effects on the Rumen Microbiome: Different Sequencing Methods Tell Different Stories

The current study employed both amplicon and shotgun sequencing to examine and compare the rumen microbiome in Angus bulls fed with either a backgrounding diet (BCK) or finishing diet (HG), to assess if both methods produce comparable results. Rumen digesta samples from 16 bulls were subjected for microbial profiling. Distinctive microbial profiles were revealed by the two methods, indicating that choice of sequencing approach may be a critical facet in studies of the rumen microbiome. Shotgun-sequencing identified the presence of 303 bacterial genera and 171 archaeal species, several of which exhibited differential abundance. Amplicon-sequencing identified 48 bacterial genera, 4 archaeal species, and 9 protozoal species. Among them, 20 bacterial genera and 5 protozoal species were differentially abundant between the two diets. Overall, amplicon-sequencing showed a more drastic diet-derived effect on the ruminal microbial profile compared to shotgun-sequencing. While both methods detected dietary differences at various taxonomic levels, few consistent patterns were evident. Opposite results were seen for the phyla Firmicutes and Bacteroidetes, and the genus Selenomonas. This study showcases the importance of sequencing platform choice and suggests a need for integrative methods that allow robust comparisons of microbial data drawn from various omic approaches, allowing for comprehensive comparisons across studies.

Insights into rumen microbial biosynthetic gene cluster diversity through genome-resolved metagenomics

Ruminants are critical to global food security as they transform lignocellulosic biomass into high-quality protein products. The rumen microbes ferment feed to provide necessary energy and nutrients for the ruminant host. However, we still lack insight into the metabolic processes encoded by most rumen microbial populations. In this study, we implemented metagenomic binning approaches to recover 2,809 microbial genomes from cattle, sheep, moose, deer, and bison. By clustering genomes based on average nucleotide identity, we demonstrate approximately one-third of the metagenome-assembled genomes (MAGs) to represent species not present in current reference databases and rumen microbial genome collections. Combining these MAGs with other rumen genomic datasets permitted a phylogenomic characterization of the biosynthetic gene clusters (BGCs) from 8,160 rumen microbial genomes, including the identification of 195 lanthipeptides and 5,346 diverse gene clusters for nonribosomal peptide biosynthesis. A subset of Prevotella and Selenomonas BGCs had higher expression in steers with lower feed efficiency. Moreover, the microdiversity of BGCs was fairly constant across types of BGCs and cattle breeds. The reconstructed genomes expand the genomic representation of rumen microbial lineages, improve the annotation of multi-omics data, and link microbial populations to the production of secondary metabolites that may constitute a source of natural products for manipulating rumen fermentation.

Anderson and Fernando use metagenomic binning approaches to reconstruct 2,809 microbial metagenome-assembled genomes from ruminants, and perform phylogenomic analyses on the biosynthetic gene clusters from over 8,000 total rumen microbial genomes. These genomes provide insight into the relationship between microbial populations and the production of secondary metabolites that may be important for manipulating rumen fermentation.

An integrated gene catalog and over 10,000 metagenome-assembled genomes from the gastrointestinal microbiome of ruminants

BACKGROUND

Gastrointestinal tract (GIT) microbiomes in ruminants play major roles in host health and thus animal production. However, we lack an integrated understanding of microbial community structure and function as prior studies. are predominantly biased towards the rumen. Therefore, to acquire a microbiota inventory of the discrete GIT compartments, In this study, we used shotgun metagenomics to profile the microbiota of 370 samples that represent 10 GIT regions of seven ruminant species.

RESULTS

Our analyses reconstructed a GIT microbial reference catalog with > 154 million nonredundant genes and identified 8745 uncultured candidate species from over 10,000 metagenome-assembled genomes. The integrated gene catalog across the GIT regions demonstrates spatial associations between the microbiome and physiological adaptations, and 8745 newly characterized genomes substantially expand the genomic landscape of ruminant microbiota, particularly those from the lower gut. This substantially expands the previously known set of endogenous microbial diversity and the taxonomic classification rate of the GIT microbiome. These candidate species encode hundreds of enzymes and novel biosynthetic gene clusters that improve our understanding concerning methane production and feed efficiency in ruminants. Overall, this study expands the characterization of the ruminant GIT microbiota at unprecedented spatial resolution and offers clues for improving ruminant livestock production in the future.

CONCLUSIONS

Having access to a comprehensive gene catalog and collections of microbial genomes provides the ability to perform efficiently genome-based analysis to achieve a detailed classification of GIT microbial ecosystem composition. Our study will bring unprecedented power in future association studies to investigate the impact of the GIT microbiota in ruminant health and production. Video abstract.

Characterizing rumen microbiota and CAZyme profile of Indian dromedary camel (Camelus dromedarius) in response to different roughages

In dromedary camels, which are pseudo-ruminants, rumen or C1 section of stomach is the main compartment involved in fiber degradation, as in true ruminants. However, as camels are adapted to the harsh and scarce grazing conditions of desert, their ruminal microbiota makes an interesting target of study. The present study was undertaken to generate the rumen microbial profile of Indian camel using 16S rRNA amplicon and shotgun metagenomics. The camels were fed three diets differing in the source of roughage. The comparative metagenomic analysis revealed greater proportions of significant differences between two fractions of rumen content followed by diet associated differences. Significant differences were also observed in the rumen microbiota collected at different time-points of the feeding trial. However, fraction related differences were more highlighted as compared to diet dependent changes in microbial profile from shotgun metagenomics data. Further, 16 genera were identified as part of the core rumen microbiome of Indian camels. Moreover, glycoside hydrolases were observed to be the most abundant among all Carbohydrate-Active enzymes and were dominated by GH2, GH3, GH13 and GH43. In all, this study describes the camel rumen microbiota under different dietary conditions with focus on taxonomic, functional, and Carbohydrate-Active enzymes profiles.

Identification of the Potential Role of the Rumen Microbiome in Milk Protein and Fat Synthesis in Dairy Cows Using Metagenomic Sequencing

Simple Summary

The rumen is the main digestive and absorption organ of dairy cows. It contains abundant microorganisms and can effectively use human-indigestible plant mass. Therefore, we used metagenomics to explore the role of rumen microbes in the regulation of milk protein and fat in dairy cows. This study showed that Prevotella species and Neocallimastix californiae in the rumen of cows are related to the synthesis of milk components due to their important functions in carbohydrate, amino acid, pyruvate, insulin, and lipid metabolism and transportation metabolic pathways.

Abstract

The rumen contains abundant microorganisms that aid in the digestion of lignocellulosic feed and are associated with host phenotype traits. Cows with extremely high milk protein and fat percentages (HPF; n = 3) and low milk protein and fat percentages (LPF; n = 3) were selected from 4000 lactating Holstein cows under the same nutritional and management conditions. We found that the total concentration of volatile fatty acids, acetate, butyrate, and propionate in the rumen fluid was significantly higher in the HPF group than in the LPF group. Moreover, we identified 38 most abundant species displaying differential richness between the two groups, in which Prevotella accounted for 68.8% of the species, with the highest abundance in the HPF group. Functional annotation based on the Kyoto Encyclopedia of Gene and Genome (KEGG), evolutionary genealogy of genes: Non-supervised Orthologous Groups (eggNOG), and Carbohydrate-Active enzymes (CAZy) databases showed that the significantly more abundant species in the HPF group are enriched in carbohydrate, amino acid, pyruvate, insulin, and lipid metabolism and transportation. Furthermore, Spearman’s rank correlation analysis revealed that specific microbial taxa (mainly the Prevotella species and Neocallimastix californiae) are positively correlated with total volatile fatty acids (VFA). Collectively, we found that the HPF group was enriched with several Prevotella species related to the total VFA, acetate, and amino acid synthesis. Thereby, these fulfilled the host’s needs for energy, fat, and rumen microbial protein, which can be used for increased biosynthesis of milk fat and milk protein. Our findings provide novel information for elucidation of the regulatory mechanism of the rumen in the formation of milk composition.

Metagenomic analysis reveals a dynamic microbiome with diversified adaptive functions to utilize high lignocellulosic forages in the cattle rumen

Rumen microbiota play a key role in the digestion and utilization of plant materials by the ruminant species, which have important implications for greenhouse gas emission. Yet, little is known about the key taxa and potential gene functions involved in the digestion process. Here, we performed a genome-centric analysis of rumen microbiota attached to six different lignocellulosic biomasses in rumen-fistulated cattle. Our metagenome sequencing provided novel genomic insights into functional potential of 523 uncultured bacteria and 15 mostly uncultured archaea in the rumen. The assembled genomes belonged mainly to Bacteroidota, Firmicutes, Verrucomicrobiota, and Fibrobacterota and were enriched for genes related to the degradation of lignocellulosic polymers and the fermentation of degraded products into short chain volatile fatty acids. We also found a shift from copiotrophic to oligotrophic taxa during the course of rumen fermentation, potentially important for the digestion of recalcitrant lignocellulosic substrates in the physiochemically complex and varying environment of the rumen. Differential colonization of forages (the incubated lignocellulosic materials) by rumen microbiota suggests that taxonomic and metabolic diversification is an evolutionary adaptation to diverse lignocellulosic substrates constituting a major component of the cattle's diet. Our data also provide novel insights into the key role of unique microbial diversity and associated gene functions in the degradation of recalcitrant lignocellulosic materials in the rumen.

Rumen Epithelial Communities Share a Core Bacterial Microbiota: A Meta-Analysis of 16S rRNA Gene Illumina MiSeq Sequencing Datasets

In this meta-analysis, 17 rumen epithelial 16S rRNA gene Illumina MiSeq amplicon sequencing data sets were analyzed to identify a core rumen epithelial microbiota and core rumen epithelial OTUs shared between the different studies included. Sequences were quality-filtered and screened for chimeric sequences before performing closed-reference 97% OTU clustering, and de novo 97% OTU clustering. Closed-reference OTU clustering identified the core rumen epithelial OTUs, defined as any OTU present in ≥ 80% of the samples, while the de novo data was randomly subsampled to 10,000 reads per sample to generate phylum- and genus-level distributions and beta diversity metrics. 57 core rumen epithelial OTUs were identified including metabolically important taxa such as Ruminococcus, Butyrivibrio, and other Lachnospiraceae, as well as sulfate-reducing bacteria Desulfobulbus and Desulfovibrio. Two Betaproteobacteria OTUs (Neisseriaceae and Burkholderiaceae) were core rumen epithelial OTUs, in contrast to rumen content where previous literature indicates they are rarely found. Two core OTUs were identified as the methanogenic archaea Methanobrevibacter and Methanomethylophilaceae. These core OTUs are consistently present across the many variables between studies which include different host species, geographic region, diet, age, farm management practice, time of year, hypervariable region sequenced, and more. When considering only cattle samples, the number of core rumen epithelial OTUs expands to 147, highlighting the increased similarity within host species despite geographical location and other variables. De novo OTU clustering revealed highly similar rumen epithelial communities, predominated by Firmicutes, Bacteroidetes, and Proteobacteria at the phylum level which comprised 79.7% of subsampled sequences. The 15 most abundant genera represented an average of 54.5% of sequences in each individual study. These abundant taxa broadly overlap with the core rumen epithelial OTUs, with the exception of Prevotellaceae which were abundant, but not identified within the core OTUs. Our results describe the core and abundant bacteria found in the rumen epithelial environment and will serve as a basis to better understand the composition and function of rumen epithelial communities.

New Insights into the Co-Occurrences of Glycoside Hydrolase Genes among Prokaryotic Genomes through Network Analysis

Glycoside hydrolase (GH) represents a crucial category of enzymes for carbohydrate utilization in most organisms. A series of glycoside hydrolase families (GHFs) have been classified, with relevant information deposited in the CAZy database. Statistical analysis indicated that most GHFs (134 out of 154) were prone to exist in bacteria rather than archaea, in terms of both occurrence frequencies and average gene numbers. Co-occurrence analysis suggested the existence of strong or moderate-strong correlations among 63 GHFs. A combination of network analysis by Gephi and functional classification among these GHFs demonstrated the presence of 12 functional categories (from group A to L), with which the corresponding microbial collections were subsequently labeled, respectively. Interestingly, a progressive enrichment of particular GHFs was found among several types of microbes, and type-L as well as type-E microbes were deemed as functional intensified species which formed during the microbial evolution process toward efficient decomposition of lignocellulose as well as pectin, respectively. Overall, integrating network analysis and enzymatic functional classification, we were able to provide a new angle of view for GHs from known prokaryotic genomes, and thus this study is likely to guide the selection of GHs and microbes for efficient biomass utilization.

Metagenomic analysis of the cow, sheep, reindeer and red deer rumen

The rumen microbiota comprises a community of microorganisms which specialise in the degradation of complex carbohydrates from plant-based feed. These microbes play a highly important role in ruminant nutrition and could also act as sources of industrially useful enzymes. In this study, we performed a metagenomic analysis of samples taken from the ruminal contents of cow (Bos Taurus), sheep (Ovis aries), reindeer (Rangifer tarandus) and red deer (Cervus elaphus). We constructed 391 metagenome-assembled genomes originating from 16 microbial phyla. We compared our genomes to other publically available microbial genomes and found that they contained 279 novel species. We also found significant differences between the microbiota of different ruminant species in terms of the abundance of microbial taxonomies, carbohydrate-active enzyme genes and KEGG orthologs. We present a dataset of rumen-derived genomes which in combination with other publicly-available rumen genomes can be used as a reference dataset in future metagenomic studies.