Its Role in Ruminant Nutrition and Its Potential Industrial Application for Organic Acid Biosynthesis.

The Gram-negative, strictly anaerobic bacterium was first isolated from the rumen in 1953 and is common in the mammalian gastrointestinal tract. Its ability to use either lactate or glucose as its major energy sources for growth has been well documented, although it can also ferment amino acids into ammonia and branched-chain fatty acids, which are growth factors for other bacteria. The ruminal abundance of usually increases in animals fed grain-based diets due to its ability to use lactate (the product of rapid ruminal sugar fermentation), especially at a low ruminal pH (<5.

Degradation of Cellulose and Hemicellulose by Ruminal Microorganisms.

As major structural components of plant cell walls, cellulose and hemicellulose are degraded and fermented by anaerobic microbes in the rumen to produce volatile fatty acids, the main nutrient source for the host. Cellulose degradation is carried out primarily by specialist bacteria, with additional contributions from protists and fungi, via a variety of mechanisms. Hemicelluloses are hydrolyzed by cellulolytic bacteria and by generalist, non-cellulolytic microbes, largely via extracellular enzymes.

Microbial communities for valorizing biomass using the carboxylate platform to produce volatile fatty acids: A review.

The carboxylate platform employs a diverse microbial consortium of anaerobes in which the methanogens are inhibited. Nearly all biomass components are digested to a mixture of C1-C8 monocarboxylic acids and their corresponding salts. The methane-arrested anaerobic digestion proceeds readily without needing to sterilize biomass or equipment.

Effects of preservation of rumen inoculum on volatile fatty acids production and the community dynamics during batch fermentation of fruit pomace.

Rumen fluid (RF) as inocula is useful for evaluating biomass digestibility and has potential for producing volatile fatty acids (VFA) via the carboxylate platform. However, RF is not readily available, necessitating evaluation of potential preservation methods. Glycerol (50% v/v) and DMSO (5% v/v) were used to preserve rumen inocula for 3 months at -80 °C.

Assignment of virus and antimicrobial resistance genes to microbial hosts in a complex microbial community by combined long-read assembly and proximity ligation.

We describe a method that adds long-read sequencing to a mix of technologies used to assemble a highly complex cattle rumen microbial community, and provide a comparison to short read-based methods. Long-read alignments and Hi-C linkage between contigs support the identification of 188 novel virus-host associations and the determination of phage life cycle states in the rumen microbial community. The long-read assembly also identifies 94 antimicrobial resistance genes, compared to only seven alleles in the short-read assembly.

Valorisation of the invasive species, Prosopis juliflora, using the carboxylate platform to produce volatile fatty acids.

Biomass derived from low-value, high-volume invasive plant species is an attractive, alternative feedstock to produce biofuels and biochemicals. This study aimed to use the carboxylate platform to valorize the invasive leguminous shrub, Prosopis juliflora (Mesquite), by utilizing in vitro rumen fermentations without chemical pretreatment to produce volatile fatty acids. The three fractions of the mesquite: leaves (ProL), stems (ProS) and branches (ProB) were compared regarding chemical composition, neutral detergent fiber (NDF) digestibility at 7 time points and VFA production after 72 h with sugarcane bagasse (SCB) as a reference.

Shifts in fermentation end products and bacterial community composition in long-term, sequentially transferred in vitro ruminal enrichment cultures fed switchgrass with and without ethanol as a co-substrate.

In vitro ruminal fermentations resemble in vivo fermentations with respect to substrate consumption and distribution of fermentation products in short term (1-5 d) incubations. However, little is known regarding changes in in vitro fermentations over prolonged incubation or multiple transfers. Gas production, pH, fermentation products, and bacterial community composition were examined in duplicate in vitro fermentations of switchgrass plus distillers grains that were transferred at 3-4 d intervals over 900 d.

A global analysis of gene expression in S85 grown on cellulose and soluble sugars at different growth rates.

Background: Cellulose is the most abundant biological polymer on earth, making it an attractive substrate for the production of next-generation biofuels and commodity chemicals. However, the economics of cellulose utilization are currently unfavorable due to a lack of efficient methods for its hydrolysis. strain S85, originally isolated from the bovine rumen, is among the most actively cellulolytic mesophilic bacteria known, producing succinate as its major fermentation product.

Diet Influences Early Microbiota Development in Dairy Calves without Long-Term Impacts on Milk Production.

Gastrointestinal tract (GIT) microorganisms play important roles in the health of ruminant livestock and affect the production of agriculturally relevant products, including milk and meat. Despite this link, interventions to alter the adult microbiota to improve production have proven ineffective, as established microbial communities are resilient to change. In contrast, developing communities in young animals may be more easily altered but are less well studied.

Camelina Seed Supplementation at Two Dietary Fat Levels Change Ruminal Bacterial Community Composition in a Dual-Flow Continuous Culture System.

This experiment aimed to determine the effects of camelina seed (CS) supplementation at different dietary fat levels on ruminal bacterial community composition and how it relates to changes in ruminal fermentation in a dual-flow continuous culture system. Diets were randomly assigned to 8 fermenters (1,200-1,250 mL) in a 2 × 2 factorial arrangement of treatments in a replicated 4 × 4 Latin square with four 10-day experimental periods that consisted of 7 days for diet adaptation and 3 days for sample collection. Treatments were: (1) no CS at 5% ether extract (EE, NCS5); (2) no CS at 8% EE (NCS8); (3) 7.

Transient changes in milk production efficiency and bacterial community composition resulting from near-total exchange of ruminal contents between high- and low-efficiency Holstein cows.

The objectives of this study were to determine if milk production efficiency (MPE) is altered by near-total exchange of ruminal contents between high- (HE) and low-MPE (LE) cows and to characterize ruminal bacterial community composition (BCC) before exchange and over time postexchange. Three pairs of ruminally cannulated, third-lactation cows were selected whose MPE (energy-corrected milk per unit of dry matter intake) differed over their first 2 lactations. Approximately 95% of ruminal contents were exchanged between cows within each pair.

Fermentation of model hemicelluloses by Prevotella strains and Butyrivibrio fibrisolvens in pure culture and in ruminal enrichment cultures.

Hemicelluloses are major components of plant biomass, but their fermentation in the rumens of cattle and other ruminants is poorly understood. We compared four species of the ruminally dominant genus Prevotella and the well-known hemicellulose utilizer, Butyrivibrio fibrisolvens, with respect to degradation of several isolated hemicelluloses (xylans, glucomannan, and xyloglucan). We also performed Illumina sequencing of the V3/V4 region of 16S rRNA genes to determine the relative proportions of Prevotella and Butyrivibrio in hemicellulose-fed enrichment cultures inoculated from ruminal contents of dairy cattle fed a total mixed ration (TMR) rich in hemicelluloses.

Impacts of ruminal microorganisms on the production of fuels: how can we intercede from the outside?

The ruminal microbiome rapidly converts plant biomass to short-chain fatty acids (SCFA) that nourish the ruminant animal host. Because of its high species diversity, functional redundancy, and ease of extraruminal cultivation, this mixed microbial community is a particularly accomplished practitioner of the carboxylate platform for producing fuels and chemical precursors. Unlike reactor microbiomes derived from anaerobic digesters or sediments, the ruminal community naturally produces high concentrations of SCFA, with only modest methane production owing to the absence of both proton-reducing acetogens and aceticlastic methanogens.

Diet specialization selects for an unusual and simplified gut microbiota in two- and three-toed sloths.

Symbiotic microbial communities are critical to the function and survival of animals. This relationship is obligatory for herbivores that engage gut microorganisms for the conversion of dietary plant materials into nutrients such as short-chain organic acids (SCOAs). The constraint on body size imposed by their arboreal lifestyle is thought to make this symbiosis especially important for sloths.

Redox mediators modify end product distribution in biomass fermentations by mixed ruminal microbes in vitro.

The fermentation system of mixed ruminal bacteria is capable of generating large amounts of short-chain volatile fatty acids (VFA) via the carboxylate platform in vitro. These VFAs are subject to elongation to larger, more energy-dense products through reverse β-oxidation, and the resulting products are useful as precursors for liquid fuels production. This study examined the effect of several redox mediators (neutral red, methyl viologen, safranin O, tannic acid) as alternative electron carriers for mixed ruminal bacteria during the fermentation of biomass (ground switchgrass not subjected to other pretreatments) and their potential to enhance elongation of end-products to medium-chain VFAs with no additional run-time.

Ruminal Bacterial Community Composition in Dairy Cows Is Dynamic over the Course of Two Lactations and Correlates with Feed Efficiency.

Fourteen Holstein cows of similar ages were monitored through their first two lactation cycles, during which ruminal solids and liquids, milk samples, production data, and feed consumption data were collected for each cow during early (76 to 82 days in milk [DIM]), middle (151 to 157 DIM), and late (251 to 257 DIM) lactation periods. The bacterial community of each ruminal sample was determined by sequencing the region from V6 to V8 of the 16S rRNA gene using 454 pyrosequencing. Gross feed efficiency (GFE) for each cow was calculated by dividing her energy-corrected milk by dry matter intake (ECM/DMI) for each period of both lactation cycles.

Redundancy, resilience, and host specificity of the ruminal microbiota: implications for engineering improved ruminal fermentations.

The ruminal microbial community is remarkably diverse, containing 100s of different bacterial and archaeal species, plus many species of fungi and protozoa. Molecular studies have identified a "core microbiome" dominated by phyla Firmicutes and Bacteroidetes, but also containing many other taxa. The rumen provides an ideal laboratory for studies on microbial ecology and the demonstration of ecological principles.

Bacterial communities in the rumen of Holstein heifers differ when fed orchardgrass as pasture vs. hay.

The rich and diverse microbiota of the rumen provides ruminant animals the capacity to utilize highly fibrous feedstuffs as their energy source, but there is surprisingly little information on the composition of the microbiome of ruminants fed all-forage diets, despite the importance of such agricultural production systems worldwide. In three 28-day periods, three ruminally-cannulated Holstein heifers sequentially grazed orchardgrass pasture (OP), then were fed orchardgrass hay (OH), then returned to OP. These heifers displayed greater shifts in ruminal bacterial community composition (determined by automated ribosomal intergenic spacer analysis and by pyrotag sequencing of 16S rRNA genes) than did two other heifers maintained 84 d on the same OP.

Unique aspects of fiber degradation by the ruminal ethanologen Ruminococcus albus 7 revealed by physiological and transcriptomic analysis.

Background: Bacteria in the genus Ruminococcus are ubiquitous members of the mammalian gastrointestinal tract. In particular, they are important in ruminants where they digest a wide range of plant cell wall polysaccharides. For example, Ruminococcus albus 7 is a primary cellulose degrader that produces acetate usable by its bovine host.

Production of medium-chain volatile fatty acids by mixed ruminal microorganisms is enhanced by ethanol in co-culture with Clostridium kluyveri.

Mixed bacterial communities from the rumen ferment cellulosic biomass primarily to C2-C4 volatile fatty acids, and perform only limited chain extension to produce C5 (valeric) and C6 (caproic) acids. The aim of this study was to increase production of caproate and valerate in short-term in vitro incubations. Co-culture of mixed ruminal microbes with a rumen-derived strain of the bacterium Clostridium kluyveri converted cellulosic biomass (alfalfa stems or switchgrass herbage) plus ethanol to VFA mixtures that include valeric and caproic acids as the major fermentation products over a 48-72h run time.

Improving ethanol production from alfalfa stems via ambient-temperature acid pretreatment and washing.

The concept of co-production of liquid fuel (ethanol) along with animal feed on farm was proposed, and the strategy of using ambient-temperature acid pretreatment, ensiling and washing to improve ethanol production from alfalfa stems was investigated. Alfalfa stems were separated and pretreated with sulfuric acid at ambient-temperature after harvest, and following ensiling, after which the ensiled stems were subjected to simultaneous saccharification and fermentation (SSF) for ethanol production. Ethanol yield was improved by ambient-temperature sulfuric acid pretreatment before ensiling, and by washing before SSF.

A syndrome of mutualism reinforces the lifestyle of a sloth.

Arboreal herbivory is rare among mammals. The few species with this lifestyle possess unique adaptions to overcome size-related constraints on nutritional energetics. Sloths are folivores that spend most of their time resting or eating in the forest canopy.

Changes in rumen bacterial community composition in steers in response to dietary nitrate.

The effect of dietary nitrate supplementation on rumen bacterial community composition was examined in beef steers fed either a nitrate-N diet or urea-N diet. An automated method of ribosomal intergenic spacer analysis was applied to solid and liquid fractions of ruminal contents to allow comparison of bacterial communities. Supplemental N source affected relative population size of four amplicon lengths (ALs) in the liquid fraction and three ALs in the solid fraction.

In vitro degradation and fermentation of three dietary fiber sources by human colonic bacteria.

Although clinical benefits of dietary fiber supplementation seem to depend partially on the extent of fiber degradation and fermentation by colonic bacteria, little is known about the effect of supplemental fiber type on bacterial metabolism. In an experiment using a nonadapted human bacterial population from three normal subjects, the extent of in vitro fermentation was greater for gum arabic (GA) than for psyllium (PSY), which was greater than that for carboxymethylcellulose (CMC). In a separate experiment, in vitro incubation with feces from 52 subjects with fecal incontinence, before and after random assignment to and consumption of one of three fiber (GA, PSY, or CMC) supplements or a placebo for 20-21 days, indicated that prior consumption of a specific fiber source did not increase its degradation by fecal bacteria.