Microbial ecology and activities in the rumen: Part II

Comparative untargeted metabolome analysis of ruminal fluid and feces of Nelore steers (Bos indicus)

We conducted a study to identify the fecal metabolite profile and its proximity to the ruminal metabolism of Nelore steers based on an untargeted metabolomic approach. Twenty-six Nelore were feedlot with same diet during 105 d. Feces and rumen fluid were collected before and at slaughter, respectively. The metabolomics analysis indicated 49 common polar metabolites in the rumen and feces. Acetate, propionate, and butyrate were the most abundant polar metabolites in both bio-samples. The rumen presented significantly higher concentrations of the polar compounds when compared to feces (P < 0.05); even though, fecal metabolites presented an accentuated representability of the ruminal fluid metabolites. All fatty acids present in the ruminal fluid were also observed in the feces, except for C20:2n6 and C20:4n6. The identified metabolites offer information on the main metabolic pathways (higher impact factor and P < 0.05), as synthesis and degradation of ketone bodies; the alanine, aspartate and glutamate metabolisms, the glycine, serine; and threonine metabolism and the pyruvate metabolism. The findings reported herein on the close relationship between the ruminal fluid and feces metabolic profiles may offer new metabolic information, in addition to facilitating the sampling for metabolism investigation in animal production and health routines.

Stochasticity constrained by deterministic effects of diet and age drive rumen microbiome assembly dynamics

How complex communities assemble through the animal's life, and how predictable the process is remains unexplored. Here, we investigate the forces that drive the assembly of rumen microbiomes throughout a cow's life, with emphasis on the balance between stochastic and deterministic processes. We analyse the development of the rumen microbiome from birth to adulthood using 16S-rRNA amplicon sequencing data and find that the animals shared a group of core successional species that invaded early on and persisted until adulthood. Along with deterministic factors, such as age and diet, early arriving species exerted strong priority effects, whereby dynamics of late successional taxa were strongly dependent on microbiome composition at early life stages. Priority effects also manifest as dramatic changes in microbiome development dynamics between animals delivered by C-section vs. natural birth, with the former undergoing much more rapid species invasion and accelerated microbiome development. Overall, our findings show that together with strong deterministic constrains imposed by diet and age, stochastic colonization in early life has long-lasting impacts on the development of animal microbiomes.

Archaea in the microbial community of the reindeer rumen in the Russian Arctic

Archaea is the least studied group of the reindeer rumen microbiocenosis. Although the functional load performed by this group of microorganisms in the rumen is large. Methane-forming archaea play a key role in the process of anaerobic decomposition of organic substances, the formation of methane. This study for the first time analyzed the composition of the archaeal part of the microbial community of the reindeer rumen using the T-RFLP method from various regions of the Russian Arctic. As a result, it was found that according to the estimates of the number of archaea by quantitative PCR in the reindeer rumen in the winter-spring period, on average, 108 genomes/g of archaea were observed in individuals of the Yamalo-Nenets Autonomous District, and 109 genomes/in animals from the Nenets Autonomous District Archean. Thus, in the winter-spring period, a lower number of archaea in the rumen was observed in the Yamalo-Nenets Autonomous District. According to the results of the T-RFLP method, 44 to 134 phylotypes were detected in the archaeal community of the reindeer rumen, the Shannon index was 2.02–3.80. The lowest content (up to 11.10 %) of methanogenic archaea of the Methanomicrobia class (including the families Methanosarcinaceae and Methanocorpusculaceae) was revealed in the Nenets Autonomous District, while their presence in individuals of the Yamalo-Nenets Autonomous District reached 36.33 %. Interestingly, in adults of the Yamalo-Nenets and Nenets Autonomous Districts, a significant decrease in the representation of methanogenic archaea of the Methanomicrobia class was noted by 1.38 (P <0.05) and 2.70 times (P <0.01), respectively, compared with young individuals (up to 2 years).

Effects of gallic acid on in vitro rumen fermentation and methane production using rumen simulation (Rusitec) and batch-culture techniques

Two experiments were conducted to investigate the effects of adding gallic acid (GA) to ruminant diets on long- and short-term in vitro rumen fermentation and methane (CH4) production, and to test possible interactions between GA and ethanol on fermentation. The first experiment was conducted using the rumen simulation technique (Rusitec), as a completely randomised block design with four replications and the following four doses of GA: 0, 5, 10 and 20 mg GA/g dry matter (DM). Ethanol was used in all treatments to increase the solubilisation of GA in rumen fluid. The experimental period lasted 16 days, of which the first 7 days were for adaptation and the subsequent 9 days were for sampling. The second experiment was a 48-h batch-culture incubation conducted as a completely randomised design with a 4 (GA dose; 0, 10, 20, and 40 mg GA/g DM) × 2 (with or without ethanol) arrangement of treatments. In the Rusitec experiment, addition of GA up to 20 mg/g DM did not affect DM disappearance (DMD), organic matter (OM) disappearance, neutral detergent-fibre disappearance (NDFD), acid detergent-fibre disappearance (ADFD) or starch disappearance (P &gt; 0.05), but crude protein disappearance was linearly decreased (P = 0.04) from 78.3% to 72.0%. Daily gas production and CH4 production expressed as mL/g DM and mL/g DMD were not affected by addition of GA (P &gt; 0.05). Addition of GA up to 20 mg/g DM increased butyrate and isovalerate production (P &lt; 0.05) and tended to increase isobutyrate (P = 0.09) and decrease heptanoate production (P = 0.07). In the batch-culture experiment, adding GA up to 40 mg/g DM linearly increased 48-h DMD, NDFD and ADFD (P &lt; 0.05) and decreased (P &lt; 0.05) CH4 expressed as mL/g DMD, mL/g NDFD and mL/g ADFD. Methane production was decreased after 24 h and 48 h only when GA was added at 10 mg/g DM without ethanol. Fermentation liquid pH and concentration of ammonia-nitrogen (ammonia-N) were also reduced (P &lt; 0.05) with an increasing concentration of GA. Treatments with ethanol notably enhanced 48-h DMD, NDFD, ADFD, gas production (mL/g DM, mL/g OM or mL/g DMD), CH4 production (mL/g DM, mL/g DMD or mL/g NDFD), total volatile fatty acid concentration, the acetate:propionate ratio, acetate, valerate, isovalerate and caproate molar proportions (P &lt; 0.01) and decreased propionate, butyrate and isobutyrate molar proportions (P &lt; 0.01). Significant dose of GA × ethanol interaction was observed only for acetate molar proportion (P = 0.03). In conclusion, our study suggests that the beneficial effects of GA on feed digestion and CH4 production may be short term, while improvements in N metabolism may be sustained over the long term. It may be useful to conduct long-term in vivo studies using a range of diets and doses to verify whether GA can be used as a feed additive to mitigate enteric CH4 production and improve N metabolism of ruminants.

Contribution of different rumen microbial groups to gas, short-chain fatty acid and ammonium production from different diets-an approach in an in vitro fermentation system

In this study, the relative contribution of different microbial groups to ruminal metabolism was investigated for different diets. The rumen microbial cultures included whole rumen fluid, fungi + protozoa, bacteria + protozoa, protozoa and bacteria + fungi and were established by physical and chemical methods. Gas production, short-chain fatty acid (SCFA) and ammonium production were measured at 24 hr in in vitro incubations using the Hohenheim gas test (HGT) procedure. Seven donor animal diets with different concentrate-to-roughage ratios (C:R: 10:90, 30:70, 50:50, 70:30, 70:30BC (BC = NaHCO₃ ), 90:10 and 90:10BC) and five HGT diets (C:R: 10:90, 30:70, 50:50, 70:30 and 90:10) were formulated. Incubations in the HGT were always based on inoculum from sheep diets with the respective C:R ratio. Gas and ammonium production increased (p < 0.001) as a result of a gradual increase in concentrate proportion of the diets. In general, SCFA production followed the same trend. Whole rumen fluid and bacteria + fungi produced approximately 50% higher gas volume than protozoa and fungi + protozoa fractions, whereas gas production with bacteria + protozoa was at an intermediate level. Coculture of protozoa either with bacteria or with fungi produced more ammonium. Populations without bacteria were characterized by a particularly high acetate/propionate ratio. Although an interaction between microbial group and diet was observed for several variables, no clear direction could be established. Manipulating rumen fluid by selectively suppressing specific rumen microbial groups may be a helpful tool in elucidating their role in nutrient degradation and turnover in vitro.

The rumen microbial metagenome associated with high methane production in cattle

Background

Methane represents 16 % of total anthropogenic greenhouse gas emissions. It has been estimated that ruminant livestock produce ca. 29 % of this methane. As individual animals produce consistently different quantities of methane, understanding the basis for these differences may lead to new opportunities for mitigating ruminal methane emissions. Metagenomics is a powerful new tool for understanding the composition and function of complex microbial communities. Here we have applied metagenomics to the rumen microbial community to identify differences in the microbiota and metagenome that lead to high- and low-methane-emitting cattle phenotypes.

Methods

Four pairs of beef cattle were selected for extreme high and low methane emissions from 72 animals, matched for breed (Aberdeen-Angus or Limousin cross) and diet (high or medium concentrate). Community analysis was carried out by qPCR of 16S and 18S rRNA genes and by alignment of Illumina HiSeq reads to the GREENGENES database. Total genomic reads were aligned to the KEGG genes databasefor functional analysis.

Results

Deep sequencing produced on average 11.3 Gb per sample. 16S rRNA gene abundances indicated that archaea, predominantly Methanobrevibacter, were 2.5× more numerous (P = 0.026) in high emitters, whereas among bacteria Proteobacteria, predominantly Succinivibrionaceae, were 4-fold less abundant (2.7 vs. 11.2 %; P = 0.002). KEGG analysis revealed that archaeal genes leading directly or indirectly to methane production were 2.7-fold more abundant in high emitters. Genes less abundant in high emitters included acetate kinase, electron transport complex proteins RnfC and RnfD and glucose-6-phosphate isomerase. Sequence data were assembled de novo and over 1.5 million proteins were annotated on the subsequent metagenome scaffolds. Less than half of the predicted genes matched matched a domain within Pfam. Amongst 2774 identified proteins of the 20 KEGG orthologues that correlated with methane emissions, only 16 showed 100 % identity with a publicly available protein sequence.

Conclusions

The abundance of archaeal genes in ruminal digesta correlated strongly with differing methane emissions from individual animals, a finding useful for genetic screening purposes. Lower emissions were accompanied by higher Succinovibrionaceae abundance and changes in acetate and hydrogen production leading to less methanogenesis, as similarly postulated for Australian macropods. Large numbers of predicted protein sequences differed between high- and low-methane-emitting cattle. Ninety-nine percent were unknown, indicating a fertile area for future exploitation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2032-0) contains supplementary material, which is available to authorized users.

Isolation and Characterization of Xylan-Degrading Strains of Butyrivibrio fibrisolvens from a Napier Grass-Fed Anaerobic Digester

Six new xylanolytic bacterial strains have been isolated from a Napier grass-fed anaerobic digester. These strains were identified as Butyrivibrio fibrisolvens and were similar in many respects to ruminal isolates described previously. The new isolates exhibited a high degree of DNA homology with several ruminal strains of B. fibrisolvens. Xylan or xylose was required to induce the production of enzymes for xylan degradation, xylanase and xylosidase. Production of these enzymes was repressed in the presence of glucose. Xylanase activity was predominantly extracellular, while that of xylosidases was cell associated. The new isolates of B. fibrisolvens grew well in defined medium containing xylan as the sole carbon source and did not produce obvious slime or capsular layers. These strains may be useful for future genetic investigations.

Microbial aggregates in anaerobic wastewater treatment

The phenomenon aggregation of anaerobic bacteria gives an opportunity to speed up the digestion rate during methanogenesis. The aggregates are mainly composed of methanogenic bacteria which convert acetate and H2/CO2 into methane. Other bacteria are also included in the aggregates but their concentration is rather small. The aggregates may also be formed during acetogenesis or even hydrolysis but such aggregates are not stable and disrupt quickly when not fed. A two stage process seems to be suitable when high concentrated solid waste must be treated. Special conditions are necessary to promote aggregate formation from methanogenic bacteria but aggregates once formed are stable without feeding even for a few years. The structure, texture and activity of bacterial aggregates depend on several parameters: (1)--temperature and pH, (2)--wastewater composition and (3)--hydrodynamic conditions within the reactor. The common influence of all these parameters is still rather unknown but some recommendations may be given. Temperature and pH should be maintained in the range which is optimal for methanogenic bacteria e.g. a temperature between 32 and 50 degrees C and a value pH between 6.5 and 7.5. Wastewaters should contain soluble wastes and the specific loading rate should be around one kgCOD(kgVSS)-1 d-1. The concentration of the elements influences aggregate composition and probably structure and texture. At high calcium concentration a change in the colour of the granules has been observed. Research is necessary to investigate the influence of other elements and organic toxicants on maintenance of the aggregates. Hydrodynamic conditions seem to influence the stability of the granules over long time periods. At low liquid stream rates, aggregates may starve and lysis within the aggregates is possible which results in hollowing of aggregates and their floating. At high liquid stream rates the aggregates may be disrupted and washed out of the reactor as a flocculent sludge. Methanogenic bacterial aggregates have been successfully applied in many full scale installations, especially for sugar beet, potato, pulp and paper mill, and other soluble wastes. The UASB reactors used for these treatments are simple in construction and handling which result in rather low total costs. A further and wider application of UASB reactors and methanogenic aggregates for various industrial wastewaters is expected.

In vitro fermentation of cellulosis amorphous and meadow hay in experimentally Ascaris suum-infected lambs

The objective of this experiment was to determine the effect of rumen inocula from experimentally Ascaris suum (AS)-infected lambs on cellulose amorphous (CA) and meadow hay (MH) used as substrates during 72h incubation in vitro. The rumen inocula were obtained post-mortem from eight lambs that had been experimentally infected with 1000 AS eggs per lamb daily for 3 weeks. Samples of rumen inocula were obtained from the lambs weekly throughout the experiment for 8 weeks. Two lambs were kept as uninfected control animals. The substrates were incubated together with buffered rumen fluid in sealed fermentation bottles. In vitro dry matter degradability (IVDMD), total gas, methane and total and individual fatty acid (VFA) for both incubated substrates were measured and compared by the pressure transducer technique. Comparison of the values for the controls, total gas, methane and VFA revealed significant differences (P<0.05, P<0.01, P<0.001, respectively) for both substrates. Pronounced differences (P<0.001) were also found between CA and MH especially for IVDMD, total gas and total VFA production. A decrease (P<0.001) of IVDMD, total gas, methane and total VFA was observed from week 6 to week 8. Restriction of fermentation was evident from week 7 to week 8. The results suggest that the functional damage arising from pathological lesions within the parasite-infected organs considerably affected the fermentation parameters of the incubated substrates.

Proteolytic anaerobic bacteria from lake sediments of Antarctica

Amongst twenty five proteolytic bacteria isolated from lake sediment samples of Antarctica, six isolates were selected based on SDS PAGE protein profile and zone of hydrolysis on casein agar at 10 degrees C. Most of the cultures were rod shaped and motile with two showing terminal bulging spores. Isolates grew between 5 degrees C to 37 degrees C and protease was induced in the late log, stationary or death phase. Isolate SPA-3 grew maximally at 10 degrees C and SPA-6 at 37 degrees C while others preferred 20 degrees C-30 degrees C for growth. The growth and protease production on casein, skimmed milk, bovine serum albumin and gelatin varied with the isolates. Acetate was the dominant volatile fatty acid (24-66% of total VFA) produced during hydrolysis of protein substrate.

Ecology, metabolism, and genetics of ruminal selenomonads

Selenomonas ruminantium is one of the more prominent and functionally diverse bacteria present in the rumen and can survive under a wide range of nutritional fluctuations. Selenomonas is not a degrader of complex polysaccharides associated with dietary plant cell wall components, but is important in the utilization of soluble carbohydrates released from initial hydrolysis of these polymers by other ruminal bacteria. Selenomonads have multiple carbon flow routes for carbohydrate catabolism and ATP generation, and subspecies differ in their ability to use lactate. Some soluble carbohydrates (glucose, sucrose) appear to be transported via the phosphoenolpyruvate phosphotransferase system, while arabinose and xylose are transported by proton symport. High cell yields and the presence of electron transport components in Selenomonas strains has been documented repeatedly and this may partially account for the energy partitioning observed between energy consumed for growth and maintenance functions. Most strains can utilize ammonia, protein, and/or amino acids as a nitrogen source. Some strains can hydrolyze urea and/or reduce nitrate and use the ammonia for the biosynthesis of amino acids. Experimental evidence suggests that ammonia assimilatory enzymes in some strains may possess unique properties with respect to other presumably similar bacteria. Little is known about the genetics of ruminal selenomonads. Plasmid DNA has been isolated from some strains, but it is unknown what physiological functions may be encoded on these extrachromosomal elements. Due to the predominance of S. ruminantium in the rumen, it is an ideal candidate for genetic manipulation. Once the genetics of this bacterium are better understood, it may be possible to amplify its role in the rumen.

Isolation of cellulolytic mesophilic clostridia from a municipal solid waste digestor

Ten obligately anaerobic, cellulolytic mesophilic bacteria were isolated from a municipal solid waste digestor used for biogas production. The isolates were rod-shaped, spore-forming bacteria in anaerobic conditions, and stained Gram-positive in young cultures, and hence were identified asClostridium. Small regular translucent and unpigmented colonies were observed on cellulose plates. The strains were gelatinase-negative, hydrolyzed esculin and starch, and fermented xylose and arabinose. The lecithinase, lipase, and indole tests were negative. The major fermentation products from cellulose included ethanol and acetate. The morphological and other biochemical characteristics indicated that these clostridia did not correspond to any previously described species. All the strains produced high activities of extracellular cellulases in cellulose media and degraded paper.

Identification of the Butyrivibrio fibrisolvens xylosidase gene (xylB) coding region and its expression in Escherichia coli

The gene encoding the principal Butyrivibrio fibrisolvens xylosidase (xylB) has been cloned and expressed in Escherichia coli under the control of the lac promoter. The coding region for this gene was localized within a 3.2-kilobase B. fibrisolvens DNA fragment in pUC18. A new protein band was observed in recombinant E. coli containing xylB. This protein (approximately 60,000 molecular weight) was presumed to be the xylosidase monomer. The optimal pH (5.5) and substrate range for the recombinant and native xylosidases appeared identical. Both enzymes hydrolyzed xylo-oligosaccharides with chain lengths of 2 to 5 and both were inactive on xylan.

Reconstitution of the gastrointestinal microflora of lactobacillus-free mice

A colony of mice that do not harbor lactobacilli in their digestive tracts but whose intestinal microflora is otherwise functionally similar to that of conventional animals was derived. Methods used to reconstitute the intestinal microflora of the mice included inoculation of the animals with cultures of specific microbes, noncultivable microbes attached to epithelial cells, and cecal contents from conventional mice treated with chloramphenicol. Twenty-six microflora-associated characteristics were monitored by using relatively simple tests to determine the microflora status of the mice.

Pathway and sites for energy conservation in the metabolism of glucose by Selenomonas ruminantium

On the basis of enzyme activities detected in extracts of Selenomonas ruminantium HD4 grown in glucose-limited continuous culture, at a slow (0.11 h-1) and a fast (0.52 h-1) dilution rate, a pathway of glucose catabolism to lactate, acetate, succinate, and propionate was constructed. Glucose was catabolized to phosphoenol pyruvate (PEP) via the Emden-Meyerhoff-Parnas pathway. PEP was converted to either pyruvate (via pyruvate kinase) or oxalacetate (via PEP carboxykinase). Pyruvate was reduced to L-lactate via a NAD-dependent lactate dehydrogenase or oxidatively decarboxylated to acetyl coenzyme A (acetyl-CoA) and CO2 by pyruvate:ferredoxin oxidoreductase. Acetyl-CoA was apparently converted in a single enzymatic step to acetate and CoA, with concomitant formation of 1 molecule of ATP; since acetyl-phosphate was not an intermediate, the enzyme catalyzing this reaction was identified as acetate thiokinase. Oxalacetate was converted to succinate via the activities of malate dehydrogenase, fumarase and a membrane-bound fumarate reductase. Succinate was then excreted or decarboxylated to propionate via a membrane-bound methylmalonyl-CoA decarboxylase. Pyruvate kinase was inhibited by Pi and activated by fructose 1,6-bisphosphate. PEP carboxykinase activity was found to be 0.054 mumol min-1 mg of protein-1 at a dilution rate of 0.11 h-1 but could not be detected in extracts of cells grown at a dilution rate of 0.52 h-1. Several potential sites for energy conservation exist in S. ruminantium HD4, including pyruvate kinase, acetate thiokinase, PEP carboxykinase, fumarate reductase, and methylmalonyl-CoA decarboxylase. Possession of these five sites for energy conservation may explain the high yields reported here (56 to 78 mg of cells [dry weight] mol of glucose-1) for S. ruminantium HD4 grown in glucose-limited continuous culture.

Use of phylogenetically based hybridization probes for studies of ruminal microbial ecology

To address the long-standing need for more precise descriptions of natural microbial ecosystems, 16S rRNAs were used to track certain species and phylogenetically coherent groups of microorganisms in their natural setting without culturing. Species- and group-specific 16S rRNA-targeted oligonucleotide hybridization probes were developed to enumerate various strains of Bacteroides succinogenes and Lachnospira multiparus-like organisms in the bovine rumen before, during, and after perturbation of that ecosystem by the addition of the ionophore antibiotic monensin. Based on probe hybridization, relative numbers of L. multiparus-like organisms were depressed about 2-fold during monensin addition and demonstrated a transient 5- to 10-fold increase immediately after removal of the antibiotic from the diet. The most pronounced population changes were observed among different strains of B. succinogenes, as evaluated by three hybridization probes. One probe hybridized to all strains, whereas the other two identified genetically distinct groups represented by strains isolated from the rumen and from the ceca of nonruminants. The rumen-type strains predominated on most days (ca. 0.2 to 0.8% of total ribosome numbers). Their proportion transiently increased about fivefold immediately after the addition of monensin to the feed and then transiently fell below the average premonensin level. During this time (ca. 2 weeks after monensin addition) the cecal type predominated (ca. 0.1 to 0.2%). Cultural enumeration of B. succinogenes on nonselective agar and by observing clearings in cellulose agar media were largely unsuccessful due to the low number of organisms present and the predominance of other cellulolytic species.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting the rate of breakdown of bacterial protein in rumen fluid

1. The cellular proteins of Butyrivibrio fibrisolvens, Lactobacillus casei, Megasphaera elsdenii, Selenomonas ruminantium and Streptococcus bovis were labelled by growth in the presence of L-[14C]leucine, and the breakdown of labelled protein was measured in incubations of these bacteria with rumen fluid to which unlabelled 5 mM-L-leucine was added. The rate of protein breakdown was estimated from the rate of release of radioactivity into acid-soluble material. 2. Protein breakdown occurred at different rates in different species. The mean rates for B. fibrisolvens, L. casei, M. elsdenii, Sel. ruminantium and Str. bovis were 28.6, 18.1, 17.7, 10.5 and 5.3%/h respectively in samples of strained rumen fluid (SRF) with different protozoal populations. Rates of 3%/h or less were found in SRF from ciliate-free sheep or in faunated SRF from which protozoa had been removed by centrifugation. Further removal of mixed rumen bacteria had little effect. Suspensions of washed protozoa degraded bacterial protein at rates which were of the same order as those found in SRF. 3. The rate of breakdown of bacterial protein in different samples of SRF tended to increase as the numbers of small entodiniomorphid protozoa increased. The numbers of larger entodiniomorphs and holotrichs had no obvious influence on this rate. 4. Autoclaved and u.v.-treated bacteria were generally no different from live bacteria in their susceptibility to breakdown in SRF from faunated sheep, indicating that endogenous protein turnover was not a significant cause of bacterial protein catabolism. 5. The rate of bacterial protein breakdown was unrelated to the proteolytic activity of SRF. 6. It was concluded that predation by small protozoa is by far the most important cause of bacterial protein turnover in the rumen, with autolysis, other lytic factors and endogenous proteolysis being of minor importance.

Protein and fiber digestion, passage, and utilization in lactating cows. Microbial growth and flow as influenced by dietary manipulations

The accuracy of prediction of microbial growth in the rumen and flow of microbial protein to the small intestine is important in predicting protein and carbohydrate utilization in dairy cattle as well as the development of a protein and carbohydrate feeding system that will be an improvement over present systems. Empirical multiple and simple regression equations are presented that demonstrate the impact of body size, proportion of forage in the diet, and dry matter intake on flow of microbial protein into the small intestine from the rumen. Concepts are developed and validated for a mechanistic, dynamic approach for prediction of microbial growth and flow of microbial protein based on Michaelis-Menton equations, microbial substance affinities, and rumen liquid flow kinetics. Emphasis is placed on the importance of quantifying dynamics of rumen function, the need for experimentation to develop a carbohydrate system that will include methods for analysis, and a factorial approach to digestion and utilization.

Urease activity in gastrointestinal tract of rabbit and electrophoretic behaviour of urease

Urease activity in the stomach (fundus and antrum), caecal content and soft faeces of rabbit was studied. Significant differences between fundus and antral content (P less than 0.01) and between caecum and soft faeces (P less than 0.05) were observed. The urease zymograms from caecal content and soft faeces of rabbit presented two different bands. The fundus content and the caecal ureolytic Clostridium innocuum bacterium exhibited only one band. Band B of caecal content was not evident at pH 4, whereas band A, also present in the stomach, was observed both at pH 4 and at pH 6. The optimal pH of urease activity of stomach and caecal content was in the range of 4-5 and 5-6, respectively. A comparison of intestinal urease zymograms with those of the single ureolytic bacterial species was suggested in order to clarify their role in urea metabolism.

A sodium-stimulated membrane-bound fumarate reductase system in Bacteroides amylophilus

Membrane vesicles derived from whole cells of the strictly anaerobic rumen bacterium Bacteroides amylophilus exhibited fumarate reductase activity with NADH, FADH2, FMNH2, or reduced viologens as electron donors. The fumarate reductase system is most likely localized on the cytoplasmic side of the plasma membrane. Cytochromes and menaquinone were not detectable. The NADH-dependent activity was inactivated by oxygen, an endogenous protease, and by irradiation at 254 nm. The electron transport inhibitor HpHOQnO and Zn2+ were identified as strong inhibitors of the fumarate reductase reaction. Two types of functional SH-groups might be operative in this system as probed by ClHgSO3H. The oxidation of NADH by fumarate was stimulated by low concentrations of Na+. Concentrations of Na+ in the range of 4 to 30 mM had a pronounced influence on growth rate and cell yield of B. amylophilus. In the presence of 1 mM NaCl growth was observed only after a lag-period of 15 h.

The effect of lumen conditions on oxygen uptake in perfused omasal laminae

The vascular anatomy of the bovine omasal lamina permitted perfusion of a discrete area of the tissue. As occurs in vivo, oxygen was provided through the vascular system, while the luminal sides of the tissue could be kept in an anaerobic environment, thus allowing study of foregut tissue metabolism under physiologically realistic conditions. O2 consumption of perfused leaves in the presence of anaerobic buffer was 64.9 and 73.5 nmol O2/mg dry weight per h in Expts 1 and 2 respectively, and was elevated (P less than 0.05) when the lumen side of the tissue was exposed to an atmosphere of nitrogen gas. In Expt 1, the rate of O2 consumption was increased (P less than 0.01) by 35% as a result of suspension of a boiled preparation of rumen micro-organisms and particles (less than 1 mm) in the anaerobic lumen buffer. Replacement of the boiled preparation with an unboiled suspension increased O2 consumption further by 11%, but this was not statistically significant (P greater than 0.05). In Expt 2, sequential addition of the following substrates or preparations to the lumen chambers all resulted in stepwise increases (P less than 0.05) in O2 consumption; 8 mM-butyrate, boiled rumen micro-organisms and particles and, finally, unboiled rumen micro-organisms and particles. Identities of the heat-labile and heat-stable components of the microbial and particle suspensions that caused enhancement of O2 removal across the perfused tissue are discussed.

Compositions and characteristics of strains of Streptococcus bovis

Streptococcus bovis strains JB1, 26, 581AXY2, 21096C, and 45S1 grew on glucose, maltose, starch, sucrose, cellobiose, and lactose. None of these strains grew on xylose or ribose, but arabinose was a suitable energy source for strains 2109C and K27FF4. All strains grew at 45 degrees C, but incubation at 50 degrees C prevented growth. Growth was permitted in 2% sodium chloride, but 6.5% sodium chloride was inhibitory. Doubling times ranged from 24 to 27 min, and final pH on glucose was approximately 4.6. None of the strains had a requirement for amino acids, and growth was rapid in media containing glucose salts and B vitamins. There was no ammonia production from arginine. All strains showed aminoendopeptidase activity, but there was considerable strain variation. Strain 7H4, reported as Streptococcus bovis, was noticeably different from the other six strains. It had a doubling time that was more than four times as long, and it grew poorly on starch or in the absence of an amino acid source. Six-and-a-half percent sodium chloride was not inhibitory, and it produced ammonia from arginine. Cell morphology was coccoid rather than ovoid. Based on these criteria, classification of strain 7H4 as Streptococcus bovis seemed doubtful. Other experiments with strain 7H4 indicated that Streptococcus bovis was devoid of diaminopimelic acid. In these experiments strain 7H4 contained significant diaminopimelic acid. The six Streptococcus bovis strains all contained diaminopimelic acid as well, but concentration varied.

Protease activities of rumen protozoa

Intact, metabolically active rumen protozoa prepared by gravity sedimentation and washing in a mineral solution at 10 to 15 degrees C had comparatively low proteolytic activity on azocasein and low endogenous proteolytic activity. Protozoa washed in 0.1 M potassium phosphate buffer (pH 6.8) at 4 degrees C and stored on ice autolysed when they were warmed to 39 degrees C. They also exhibited low proteolytic activity on azocasein, but they had a high endogenous proteolytic activity with a pH optimum of 5.8. The endogenous proteolytic activity was inhibited by cysteine proteinase inhibitors, for example, iodoacetate (63.1%) and the aspartic proteinase inhibitor, pepstatin (43.9%). Inhibitors specific for serine proteinases and metalloproteinases were without effect. The serine and cysteine proteinase inhibitors of microbial origin, including antipain, chymostatin, and leupeptin, caused up to 67% inhibition of endogenous proteolysis. Hydrolysis of casein by protozoa autolysates was also inhibited by cysteine proteinase inhibitors. Some of the inhibitors decreased endogenous deamination, in particular, phosphoramidon, which had little inhibitory effect on proteolysis. Protozoal and bacterial preparations exhibited low hydrolytic activities on synthetic proteinase and carboxypeptidase substrates, although the protozoa had 10 to 78 times greater hydrolytic activity (per milligram of protein) than bacteria on the synthetic aminopeptidase substrates L-leucine-p-nitroanilide, L-leucine-beta-naphthylamide, and L-leucinamide. The aminopeptidase activity was partially inhibited by bestatin. It was concluded that cysteine proteinases and, to a lesser extent, aspartic proteinases are primarily responsible for proteolysis in autolysates of rumen protozoa. The protozoal autolysates had high aminopeptidase activity; low deaminase activity was observed on endogenous amino acids.

Characterization of microbial proteolytic enzymes in the rumen

Up to 43% of the viable bacteria from the rumen of cows fed grass and concentrates grew on a medium containing casein as the main substrate. Proteolytic counts for a cow fed on straw and concentrates or for a hay-fed cow were lower than counts for cows fed grass and concentrates, both in absolute terms and in relation to the total anaerobic count. In crude enzyme preparations derived from the rumen protozoa, amino acid arylamidase (leucine aminopeptidase)-like activity was the main proteolytic activity observed. In enzyme preparations extracted from the rumen bacteria in the presence of Triton X-100, trypsin-like activity was predominant. Amino acid arylamidase- and metal-chelating proteinase-like activity together with lower activities of carboxypeptidase A and B and a very low chymotrypsin-like activity were found as well. Studies with enzyme inhibitors showed that the bacterial trypsin-like activity was largely of the cysteine-protease type in a hay-fed cow, but in addition comprised serine-protease activity in a cow fed grass and concentrates. Total proteolytic activity of the enzymes in the bacterial fraction and the spectrum of proteolytic enzymes were found to vary with the ration.