Analysis of peptide metabolism by ruminal microorganisms

Increasing buffering capacity enhances rumen fermentation characteristics and alters rumen microbiota composition of high-concentrate fed Hanwoo steers

The buffering capacity of buffer agents and their effects on in vitro and in vivo rumen fermentation characteristics, and bacterial composition of a high-concentrate fed Hanwoo steers were investigated in this study. Treatments were comprised of CON (no buffer added), BC0.3% (low buffering capacity, 0.3% buffer), BC0.5% (medium buffering capacity, 0.5% buffer), and BC0.9% (high buffering capacity, 0.9% buffer). Four Hanwoo steers in a 4 × 4 Latin square design were used for the in vivo trial to assess the effect of treatments. Results on in vitro experiment showed that buffering capacity, pH, and ammonia-nitrogen concentration (NH3-N) were significantly higher in BC0.9% and BC0.5% than the other treatments after 24 h incubation. Individual and total volatile fatty acids (VFA) concentration of CON were lowest compared to treatment groups. Meanwhile, in vivo experiment revealed that Bacteroidetes were dominant for all treatments followed by Firmicutes and Proteobacteria. The abundances of Barnesiella intestinihominis, Treponema porcinum, and Vibrio marisflavi were relatively highest under BC0.9%, Ruminoccocus bromii and Succiniclasticum ruminis under BC0.5%, and Bacteroides massiliensis under BC0.3%. The normalized data of relative abundance of observed OTUs' representative families have grouped the CON with BC0.3% in the same cluster, whereas BC0.5% and BC0.9% were clustered separately which indicates the effect of varying buffering capacity of buffer agents. Principal coordinate analysis (PCoA) on unweighted UniFrac distances revealed close similarity of bacterial community structures within and between treatments and control, in which BC0.9% and BC0.3% groups showed dispersed community distribution. Overall, increasing the buffering capacity by supplementation of BC0.5% and and BC0.9% buffer agents enhanced rumen fermentation characteristics and altered the rumen bacterial community, which could help prevent ruminal acidosis during a high-concentrate diet.

Effects of Dietary Supplementation with Hainanmycin on Protein Degradation and Populations of Ammonia-producing Bacteria In vitro

An in vitro fermentation was conducted to determine the effects of hainanmycin on protein degradation and populations of ammonia-producing bacteria. The substrates (DM basis) for in vitro fermentation consisted of alfalfa hay (31.7%), Chinese wild rye grass hay (28.3%), ground corn grain (24.5%), soybean meal (15.5%) with a forage: concentrate of 60:40. Treatments were the control (no additive) and hainanmycin supplemented at 0.1 (H0.1), 1 (H1), 10 (H10), and 100 mg/kg (H100) of the substrates. After 24 h of fermentation, the highest addition level of hainanmycin decreased total VFA concentration and increased the final pH. The high addition level of hainanmycin (H1, H10, and H100) reduced (p<0.05) branched-chain VFA concentration, the molar proportion of acetate and butyrate, and ratio of acetate to propionate; and increased the molar proportion of propionate, except that for H1 the in molar proportion of acetate and isobutyrate was not changed (p>0.05). After 24 h of fermentation, H10 and H100 increased (p<0.05) concentrations of peptide nitrogen and AA nitrogen and proteinase activity, and decreased (p<0.05) NH₃-N concentration and deaminase activity compared with control. Peptidase activitives were not affected by hainanmycin. Hainanmycin supplementation only inhibited the growth of Butyrivibrio fibrisolvens, which is one of the species of low deaminative activity. Hainanmycin supplementation also decreased (p<0.05) relative population sizes of hyper-ammonia-producing species, except for H0.1 on Clostridium aminophilum. It was concluded that dietary supplementation with hainanmycin could improve ruminal fermentation and modify protein degradation by changing population size of ammonia-producing bacteria in vitro; and the addition level of 10 mg/kg appeared to achieve the best results.

Peptidases of the rumen bacterium, Prevotella ruminicola

Prevotella (formerly Bacteroides) ruminicola is a numerous rumen bacterium which plays a significant role in the metabolism of proteins and peptides in the rumen. Measurement of the hydrolysis of synthetic aminopeptidase substrates by sonicated extracts and whole cells of different species of rumen bacteria indicated that P. ruminicola had the greatest range and specific activity of dipeptidyl peptidases among the species tested. Streptococcus bovis hydrolysed some dipeptidyl peptidase substrates to a lesser extent, and several species broke down Ala2-p-nitroanilide, including Ruminobacter amylophilus, Ruminococcus spp. and Veillonella parvula. Dipeptidyl peptidases, which cleave dipeptides from the amino-terminus of longer peptides, were much more active than aminopeptidases removing single amino acids in P. ruminicola. Ion-exchange chromatography of sonicated extracts of P. ruminicola M384 revealed at least four distinct activities: one hydrolysed Ala2-p-nitroanilide, ValAla-p-nitroanilide, Ala4and Ala5; another was an O2-sensitive activity hydrolysing GlyArg-4-methoxynapthylamide, ArgArg-4-methoxynaphthylamide, Gly5 and ValGlySerGlu, similar to dipeptidyl peptidase type I DPP-1); a third hydrolysed GlyPro-p-nitroanilide and GlyPro-4-methoxynapthylamide and was similar to dipeptidyl peptidase type IV XDPP-4); a fourth broke down LysAla-4-methoxynaphthylamide. All of the enzymes, and particularly those active against Ala2-p-nitroanilide and GlyPro-p-nitroanilide, were inhibited by serine protease inhibitors, and all except DPP-4 were inhibited by EDTA. Both DPP-1 and the enzyme hydrolysing LysAla-4-methoxynaphthylamide were inhibited strongly by iodoacetate. DPP-4 was inhibited completely by diprotin A. Competitive inhibition experiments suggested that DPP-1 was less important than the other enzymes in the breakdown of peptide mixtures.

A pepD-like peptidase from the ruminal bacterium,Prevotella albensis

Peptidases of Prevotella spp. play an important role in the breakdown of protein to ammonia in the rumen. This study describes a peptidase cloned from Prevotella albensis M384. DNA from P. albensis was used to complement a peptidase-deficient strain of Escherichia coli, CM107. A cloned fragment, Pep581, which enabled growth of E. coli CM107, contained an ORF of 1452 bp, encoding a 484 amino acid residue protein with a calculated molecular weight of 53.2 kDa and a theoretical pI of 4.90. Pep581 shared similar sequence identity of 47% with PepD from E. coli, and it was also a metallo-aminopeptidase. A putative catalytic metal binding region was identified in Pep581, similar to that found in the related PepT (a tripeptidase) and PepA (an oligopeptidase). Gel filtration indicated Pep581 was a dimer in its native state, similar to PepD of E. coli. PepD is a broad specificity dipeptidase that has been found in several prokaryotes. The enzyme expressed from Pep581 differed from PepD enzymes previously characterised in that it hydrolysed tri- and oligopeptides in addition to dipeptides, cleaving single amino acids from the N terminus.

Cloning and functional expression of dipeptidyl peptidase IV from the ruminal bacterium Prevotella albensis M384(T)

Ruminal bacteria of the genus Prevotella play a crucial role in peptide breakdown in the rumen, a component of protein catabolism that leads to the inefficient use of dietary protein by ruminant animals. This is the first report of the cloning of a peptidase gene from a ruminal bacterium. Part of the dipeptidyl peptidase type IV (DPP-IV) gene from Prevotella albensis M384(T) was cloned using degenerate primers designed from conserved regions found within other known DPP-IV sequences. Flanking regions were determined by genomic walking. The DPP-IV gene was expressed in Escherichia coli. The cloned enzyme required a free N terminus and catalysed the removal of X-Pro dipeptide from proline-containing oligopeptides, where proline was the second residue from the N terminus. It was inhibited by serine protease inhibitors and the substrate analogue for mammalian DPP-IV, diprotin A. The properties of the cloned enzyme were similar to those of the native form in P. albensis and, in general, DPP-IVs from other organisms. The enzyme contained a conserved motif which is associated with the S9 class of prolyl oligopeptidases. The DPP-IV gene appeared not to be part of a contiguous operon. Regions with similarity to other putative promoters of Prevotella spp. were also identified. Construction of a phylogenetic tree demonstrated that the DPP-IV of P. albensis clusters with other DPP-IVs found in bacteria of the Cytophaga-Flexibacter-Bacteroidaceae (CFB) phylum, which are more closely related to eukaryotic DPP-IVs than the DPP-IV-like enzyme (PepX) of the lactic acid bacteria.

Effects of essential oils on ruminal microorganisms and their protein metabolism

A commercial blend of essential oil (EO) compounds was added to a grass, maize silage, and concentrate diet fed to dairy cattle in order to determine their influence on protein metabolism by ruminal microorganisms. EO inhibited (P < 0.05) the rate of deamination of amino acids. Pure-culture studies indicated that the species most sensitive to EO were ammonia-hyperproducing bacteria and anaerobic fungi.

Ammonia production by ruminal microorganisms and enumeration, isolation, and characterization of bacteria capable of growth on peptides and amino acids from the sheep rumen

Excessive NH(3) production in the rumen is a major nutritional inefficiency in ruminant animals. Experiments were undertaken to compare the rates of NH(3) production from different substrates in ruminal fluid in vitro and to assess the role of asaccharolytic bacteria in NH(3) production. Ruminal fluid was taken from four rumen-fistulated sheep receiving a mixed hay-concentrate diet. The calculated rate of NH(3) production from Trypticase varied from 1.8 to 19.7 nmol mg of protein(-1) min(-1) depending on the substrate, its concentration, and the method used. Monensin (5 micro M) inhibited NH(3) production from proteins, peptides, and amino acids by an average of 28% with substrate at 2 mg/ml, compared to 48% with substrate at 20 mg/ml (P = 0.011). Of the total bacterial population, 1.4% grew on Trypticase alone, of which 93% was eliminated by 5 micro M monensin. Many fewer bacteria (0.002% of the total) grew on amino acids alone. Nineteen isolates capable of growth on Trypticase were obtained from four sheep. 16S ribosomal DNA and traditional identification methods indicated the bacteria fell into six groups. All were sensitive to monensin, and all except one group (group III, similar to Atopobium minutum), produced NH(3) at >250 nmol min(-1) mg of protein(-1), depending on the medium, as determined by a batch culture method. All isolates had exopeptidase activity, but only group III had an apparent dipeptidyl peptidase I activity. Groups I, II, and IV were most closely related to asaccharolytic ruminal and oral Clostridium and Eubacterium spp. Group V comprised one isolate, similar to Desulfomonas piger (formerly Desulfovibrio pigra). Group VI was 95% similar to Acidaminococcus fermentans. Growth of the Atopobium- and Desulfomonas-like isolates was enhanced by sugars, while growth of groups I, II, and V was significantly depressed by sugars. This study therefore demonstrates that different methodologies and different substrate concentrations provide an explanation for different apparent rates of ruminal NH(3) production reported in different studies and identifies a diverse range of hyper-ammonia-producing bacteria in the rumen of sheep.

Response of forage fiber degradation by ruminal microorganisms to branched-chain volatile fatty acids, amino acids, and dipeptides

This study evaluated the effect of branched-chain volatile fatty acids (VFA; isobutyric acid, isovaleric acid), amino acids (valine, leucine), and dipeptides (valine-valine, leucine-leucine) on neutral detergent fiber (NDF) degradation by rumen microorganisms in vitro. The CP (%) and in situ NDF degradation rate (%/h) for alfalfa, bermudagrass, and pangolagrass hays, and napiergrass silage were 17.2 and 7.5, 4.7 and 3.1, 8.3 and 5.3, and 9.6 and 3.4, respectively. In vitro NDF digestibility was the lowest for bermudagrass; alfalfa and napiergrass were the highest. When the incubation contained more ammonia initially, digestibilities increased, but relative differences among forages were unchanged. Adding branched-chain VFA (2 mM) to incubations increased digestibilities more than controls on 15 out of 16 occasions. The effectiveness varied with isoacids and forages used. Amino acid (2 mM) or dipeptide (1 mM) addition consistently increased digestibility over controls. Amino acids further increased digestibility over corresponding isoacids on 14 occasions. Improvement in digestibility over control by leucine appeared to be greater than that by valine. Digestibilities with dipeptides were always greater than those with isoacids, except for one case. Dipeptide addition further increased digestibility significantly over corresponding amino acids on only six occasions, while percent improvement in digestibility numerically by dipeptides occurred in 10 cases. Valine-valine seemed to exert different effect than leucine-leucine, depending on initial ammonia availability. The results indicate that dipeptides could be more effective than isoacids and amino acids in improving NDF digestion. Forages with high CP content or rapid NDF degradation rate appeared to respond to additives to smaller degrees.

Glutamine synthetase and protease enzyme activities and growth response of ruminal bacterium Prevotella ruminicola strain B(1)4 to nitrogen source and concentration

The objective of this study was to determine the effects of varying nitrogen sources and concentrations upon glutamine synthetase and protease activities in Prevotella ruminicola strain B(1)4. Based on growth response it appears that ammonium chloride or pepticase limited P. ruminicola becomes nitrogen limited when nitrogen concentration is at 0.5 mM. However, when casein was provided as the sole source of nitrogen P. ruminicola becomes nitrogen limited at 2.5 mM. Glutamine synthetase activity was measured from mid-log phase cells grown in either nitrogen-limited or non-limited conditions. No activity was detectable in the non-limited treatments. However, in the N-limited treatments, pepticase had the highest activity (20.76 units), followed by ammonium chloride (18.72 units) and casein (14.42 units). Protease activity assays indicated that nitrogen-limited cultures had higher proteolytic activity than non-limited cultures. Moreover, these activities appeared to follow the same response pattern as the previously observed glutamine synthetase activities. The results of this study indicate that P. ruminicola strain B(1)4 protease activity may be influenced by nitrogen concentration such that activity increases when nitrogen availability decreases.

Uptake of acetylated peptides from the small intestine in sheep and their nutritive value in rats

Acetylation is a potential method for protecting dietary peptides from degradation by rumen micro-organisms. As a first step in determining the nutritive value of acetylated peptides, their disappearance in the small intestine of sheep and their ability to support growth in a rat bioassay were measured. 15N-labelled peptides were prepared from lucerne which had been grown with 15N-labelled (NH4)2SO4 in the absence of Rhizobium. Peptides were prepared by enzymic hydrolysis of the extracted protein. Two peptide preparations were made using different proteinase mixtures. These mixtures contained peptides with an average molecular weight of 559 and 522 Da. They were treated with acetic anhydride, which resulted in 85 and 88% modification respectively, and their uptake from the small intestine was determined by injecting 1 g of untreated or acetylated peptides in a Cr-EDTA solution into the jejunum of two sheep fitted with jejunal catheters and ileal cannulas. Ileal digesta were collected and analysed for Cr and 15N. The uptake of dialanine (Ala2) and N-acetyl-Ala2 were compared in a similar way. The disappearance of 15N from lucerne peptides was high (88 and 93% respectively) and this was not affected significantly by acetylation (86 and 87%). Corresponding values for Ala2 and N-acetyl-Ala2 were both 96%, as measured by HPLC. It was therefore concluded that acetylation did not affect the uptake of peptides from the small intestine in sheep. Two feeding trials were carried out with rats. The first trial was carried out with a protein-free diet to which was added 10% lactalbumin or 5% lactalbumin and then a mixture of methionine-free amino acids, either alone or supplemented with Met, Gly-Met or acetylated Gly-Met. The rats grew equally well on all sources of Met, but failed to grow significantly on the mixture of Met-free amino acids. In the second trial the diet contained casein as 5.9% of the basal diet. Additional casein, pancreatic casein hydrolysate (peptides) and acetylated pancreatic casein hydrolysate (acetylated peptides) were compared as sources of amino acids, at inclusion rates of 100 g/kg final diet. Feed intake was similar with casein and peptides treatments, but was depressed by 23% with acetylated peptides. Live weight gain was 15 and 75% lower with the peptides and acetylated peptides diets respectively. Addition of lysine, arginine or histidine did not restore feed intake or weight gain of rats receiving acetylated peptides, but feed intake was restored immediately when peptides replaced acetylated peptides. When intake was restricted to 9 g/d and acetylated casein hydrolysate replaced half of the protein in the diet, rats gained weight less rapidly (1.44 v. 1.09 g/d) and retained less N, such that only 0.36 of the acetylated peptide-N was calculated to remain available to the animal. This N retention compared with 0.70 for unmodified casein. Thus, the rat bioassay indicated that certain specific peptides may well be of high nutritive value following acetylation, but that there may be problems of inappetance and inefficient utilization with acetylated peptide mixtures.

Peptidase Activity of Human Colonic Bacteria

Aminopeptidase activities of mixed faecal suspensions from four human donors and 12 of the most numerous species of human colonic bacteria were measured using alanine oligopeptides and various dipeptidyl- and amino acyl-arylamidase substrates. The pattern of hydrolysis of Ala(4)and Ala(5)in faecal suspensions, whereby Ala(2)was the first breakdown product, suggested that the main mechanism of peptide hydrolysis was dipeptidyl peptidase. Dipeptidyl p-nitroanilides and 4-methoxynaphthylamides were broken down more rapidly than amino acyl derivatives in three out of four individuals tested, consistent with this conclusion. The predominant Bacteroides spp. of the intestine also had greater dipeptidyl peptidase activity than amino acyl aminopeptidase activity, while Bifidobacterium, Clostridium, Enterococcus and Propionibacterium spp. had a more variable pattern of peptidase activities. Thus, peptide hydrolysis in the human intestine, as in the rumen, appears to be mainly a two-stage process which is initiated by dipeptidyl peptidases present in the most numerous Bacteriodes spp.

Biochemical and mutational analysis of a gingipain-like peptidase activity from Prevotella ruminicola B(1)4 and its role in ammonia production by ruminal bacteria

A chemical mutagenesis protocol was used with the ruminal bacterium Prevotella ruminicola strain B(1)4 to generate mutant strains defective in peptidase activity. Compared with the wild-type parent strain, the isolated mutants possessed 1/10 of the enzyme activity responsible for cleavage of glycine-arginine-4-methoxy-beta-naphthylamide (Gly-Arg-MNA). A concomitant loss in activity against arginine-arginine-4-methoxy-beta-naphthylamide (Arg-Arg-MNA) was also observed. Both activities were similarly affected by various proteinase inhibitors, suggesting that the same enzyme is responsible for the Arg-Arg-MNA peptidase and Gly-Arg-MNA peptidase activities. Growth rates of wild-type and mutant strains grown in batch culture with various nitrogen sources did not differ. However, a role for the Gly-Arg-MNA peptidase activity was demonstrated in coculture experiments with gram-positive, ammonia-producing ruminal bacteria. The rate and extent of ammonia production were reduced by approximately 25% in cocultures containing the mutants when compared with that of wild-type-containing cultures. These reductions could not be accounted for simply by the decrease in ammonia production by the mutant strain alone. To our knowledge, this paper reports the first successful use of chemical mutagenesis with ruminal microorganisms.

Degradation of protein and utilization of the hydrolytic products by a predominant ruminal bacterium, Prevotella ruminicola B1(4)

Degradation and utilization of protein by Prevotella ruminicola B1(4), a proteolytic bacterium that is prominent in the rumen, was examined. In preliminary experiments, proteinaceous N sources produced faster growth rates than did NH4Cl, based on changes in optical density over time. However, ammonium chloride produced a greater maximum cell density than did proteinaceous N sources. Of the proteinaceous N sources, an enzymatic hydrolysate of soybean protein with a relative peptide size of 3 AA residues produced a greater growth rate and maximum cell density compared with the other proteinaceous N sources. Further experiments revealed that P. ruminicola B1(4) grew faster and to a greater final dry weight with soybean protein than with casein. Degradation of both proteins was low as was indicated by the slow disappearance of soluble protein, low concentrations of free AA and peptides, and the decrease in ammonia concentrations over time. Patterns of degradation did differ between the two proteins, however. Accumulation of peptides and free AA from soybean protein peaked 2 h earlier than those from casein, and concentrations of free AA and peptides from soybean protein were lower on average than those from casein. Prevotella ruminicola B1(4) preferentially utilized Asp, Ile, Leu, Lys, and Arg from soybean protein compared with casein. The relative size of peptides that accumulated from both proteins, as determined by the ratio of ninhydrin reaction after HCl hydrolysis to ninhydrin reaction before HCl hydrolysis, suggested that part of the proteolytic activity of P. ruminicola B1(4) is a dipeptidase. Our findings suggest that P. ruminicola may have a greater impact on peptide degradation than on protein degradation in the rumen.

Characterization of proteolytic activities of rumen bacterial isolates from forage-fed cattle

The proteolytic activities of eight strains of ruminal bacteria isolated from New Zealand cattle were characterized with respect to their cellular location, response to proteinase inhibitors and hydrolysis of artificial proteinase substrates. The Streptococcus bovis strains had predominantly cell-bound activity, which included a mixture of serine and cysteine-type proteinases which had high activity against leucine p-nitroanilide (LPNA). The Eubacterium strains had a mainly cell-associated activity with serine and metallo-type proteinases which showed high activity against the chymotrypsin substrate, N-succinyl alanine alanine phenylalanine proline p-nitroanilide (NSAAPPPNA) and some LPNA activity. A Butyrivibrio strain, C211, had a cell-bound mixture of cysteine and metallo-proteinase activities and strongly hydrolysed NSAAPPPNA and LPNA while the high activity Butyrivibrio-like strain, B316, had a cell-bound, mainly serine proteinase activity which strongly hydrolysed NSAAPPPNA. A Prevotella-like strain, C21a, had a mixture of cysteine, serine and metallo-proteinase activities which were cell-bound and hydrolysed LPNA. The activities of these strains did not match those of the bacterial fraction of rumen fluid, which contained activities mainly of the cysteine type with specificity towards the substrate N-succinyl phenylalanine p-nitroanilide. The contribution of these strains to proteolysis in the rumen is discussed.

The NAD(P)H-dependent glutamate dehydrogenase activities of Prevotella ruminicola B(1)4 can be attributed to one enzyme (GdhA), and gdhA expression is regulated in response to the nitrogen source available for growth

Prevotella ruminicola B(1)4 possesses both NADPH- and NADH-linked glutamate dehydrogenase (GDH) activities, with the greatest specific activity being measured from ammonia-limited cultures. Relative to cells grown in the presence of 1 mM ammonium chloride, the NADPH-dependent activity was decreased approximately 10-fold when peptides were provided as a nitrogen source. Nondenaturing polyacrylamide gel electrophoresis (PAGE) was used to visualize the GDH protein(s) in cell extracts of P. ruminicola. For all growth conditions tested, only one GDH protein was detectable, and its relative abundance, as well as its reactivity with either NAD(P)+ or NAD(P)H, correlated well with the specific activities measured from whole-cell assays. Consistent with the findings from enzyme assays and PAGE activity gels, Northern (RNA) blot analysis revealed that expression of a gene encoding NAD(P)H-GDH activity was greatest in ammonia-grown cultures and that GDH activity is regulated in response to nitrogen source (ammonia versus peptides), probably at the level of transcription. A gene encoding the NAD(P)H-utilizing GDH activity (gdhA) was cloned, and its nucleotide sequence was determined and shown to contain an open reading frame of 1,332 bp which would encode a polypeptide of 48.8 kDa. The deduced amino acid sequence possesses three highly conserved motifs typical of family I GDHs, but several unique amino acid substitutions within these motifs were evident. These results are discussed within the context of ruminal nitrogen metabolism and the growth efficiency of succinate- and propionate-producing anaerobic bacteria.

Influence of 1,10-phenanthroline and its analogues, other chelators and transition metal ions on dipeptidase activity of the rumen bacterium, Prevotella ruminicola

Prevotella ruminicola plays a prominent role in the breakdown of peptides in the rumen, a process which contributes to excessive ammonia production and inefficient nitrogen retention in ruminants. Various metal ions and chelators were examined to assess how the metal ion-dependent dipeptidase activity of P. ruminicola M384 might be inhibited. Using sonicated extracts, Cu2+, Cr2+ and Hg2+ were most inhibitory, decreasing Ala2 breakdown to 15, 15 and 5% of control activity, whereas Co2+, Mn2+ and Zn2+ stimulated activity by 189, 30 and 26%, respectively. The chelators, EDTA, EGTA, TPEN and 1,10-phenanthroline, were inhibitory, as were several phenanthroline analogues. Among the stereoisomers of 1,10-phenanthroline tested, derivatives methylated on C-2 and C-9 were less effective than the parent molecule, but 3,4,7,8-tetramethyl-1,10-phenanthroline (TMP) was more inhibitory. Titration of the most effective inhibitors showed that EDTA, TPEN and TMP had similar potency and were effective at 0.1 mmol l-1 and above. Thus some metal ions and chelators are potent inhibitors of P. ruminicola dipeptidase, although they are unlikely to be sufficiently specific to peptide metabolism to be useful in vivo.

Inhibition by 1,10-phenanthroline of the breakdown of peptides by rumen bacteria and protozoa

The rate of peptide breakdown in the rumen frequently exceeds the rate at which the amino acids released can be used for microbial growth. The final step in this often wasteful process involves the cleavage of dipeptides. The main rumen bacterial species with high dipeptidase activity, Prevotella ruminicola, Fibrobacter succinogenes, Lachnospira multipara and Megasphaera elsdenii, had activities which were inhibited > 95% by 1,10-phenanthroline, a chelator of divalent metal ions and metalloprotease inhibitor. Dipeptidase activity in digesta taken from the rumen of sheep decreased by 33% in the presence of 1,10-phenanthroline, while mixed bacteria from the same samples were inhibited by 80% and the activity of mixed protozoa decreased by only 15%. Thus a substantial amount of dipeptide breakdown appears to be due to ciliate protozoa in the mixed population. Extensive washing of the protozoa increased the sensitivity of protozoal dipeptidase activity to 1,10-phenanthroline, suggesting that protozoa too have a metallo-dipeptidase activity but that it is normally protected from inhibition by 1,10-phenanthroline. Breakdown of the pentapeptide, Ala5, was also inhibited 27% by 1,10-phenanthroline in the mixed population, and when Trypticase, a pancreatic casein hydrolysate containing a mixture of oligopeptides, dipeptides and amino acids, was incubated with rumen fluid, the production of ammonia and free amino groups was inhibited 71% by 1,10-phenanthroline. It was concluded that metal ion chelation inhibits oligopeptidase and dipeptidase activities of rumen micro-organisms and may be a means of controlling ammonia production from peptides in the rumen.

Variations in the uptake and metabolism of peptides and amino acids by mixed ruminal bacteria in vitro

Mixed ruminal bacteria, isolated from sheep (Q and W) fed a concentrate and hay diet, were anaerobically incubated with either 14C-peptides or 14C-amino acids. Experiment 1 showed that uptake of both 14C-labeled substrates was rapid, but the rate for amino acids was twofold greater than for peptides (molecular weight, 1,000 to 200) initially but was similar after 10 min. Experiment 2 demonstrated that metabolism was also rapid; at least 90% of either 14C-labeled substrate was metabolized by 3 min. Of the radioactivity remaining in bacteria, approximately 30% was in the form of 14C-amino acids, but only in leucine, tyrosine, and phenylalanine. Supernatant radioactivity was contained only in tyrosine, phenylalanine, and mostly proline for incubations with 14C-amino acids but in up to 10 amino acids when 14C-peptides were the substrates. Short-term incubations (< 5 min; experiment 3) confirmed previous uptake patterns and showed that the experimental system was responsive to substrate competition. Experiment 4 demonstrated that bacteria from sheep Q possessed initial and maximum rates of 14C-amino acid uptake approximately fourfold greater (P < 0.01) than those of 14C-peptides, but with no significant differences (P > 0.1) between four 14C-peptide substrate groups with molecular weights of 2,000 to < 200. By contrast, bacteria from sheep W showed no such distinctions (P > 0.1) between rates for 14C-peptides and 14C-amino acids. Calculations suggested that peptides could supply from 11 to 35% and amino acids could supply from 36 to 68% of the N requirements of mixed ruminal bacteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Breakdown of N-terminally modified peptides and an isopeptide by rumen microorganisms

Treatment of Trypticase peptides with acetic anhydride, succinic anhydride, or maleic anhydride inhibited their breakdown to ammonia by rumen microorganisms by an average of 89% after 12 h of incubation in vitro. All three treatments gave similar protection. Acetylation also protected dipeptides containing lysine and methionine from degradation. However, more effective protection was obtained by linking lysine and methionine as N-epsilon-methionyl lysine.

In vitro study of the proteolytic activity of rumen anaerobic fungi

Proteolytic, aminopeptidase, endopeptidase and carboxypeptidase activities of seven strains of rumen anaerobic fungi, selected to represent the fungal population commonly found in the rumen, were investigated in vitro. Whatever the nitrogen source included in the culture medium, a proteolytic activity against the 14C-labelled casein was detected in only one fungal strain. This strain belonged to the genus Piromyces. The activity was extracellular and was found both in the culture supernatant and bound to the mycelium. No carboxypeptidase activity was detected in the seven strains. In contrast, all the strains exhibited aminopeptidase activity. Two strains had an endopeptidase activity.

Breakdown of different peptides by Prevotella (Bacteroides) ruminicola and mixed microorganisms from the sheep rumen

Several di-, tri-, and oligopeptides were incubated individually in vitro with rumen fluid from two sheep receiving a mixed grass hay/concentrate diet and with washed cells of Prevotella (formerly Bacteroides) ruminicola M384 and P. ruminicola B(1)4. The rates of breakdown of most peptides were similar in the rumen fluid from the two sheep. Acidic and proline-containing peptides tended to be more slowly degraded than neutral or basic peptides. The dipeptide at the N-terminus of higher peptides was observed as an early product of hydrolysis, confirming that a dipeptidyl aminopeptidase type of activity was present. The relative rates of breakdown of dipeptides by P. ruminicola were different from that of rumen fluid, but the hydrolysis of higher peptides followed a similar pattern, and dipeptides from the N-terminus were detected as early products.

Acetylation of peptides inhibits their degradation by rumen micro-organisms

Proteins and peptides were acetylated using acetic anhydride in order to block their N-terminal amino groups and thereby to prevent their hydrolysis by rumen microbial aminopeptidases. The effects of acetylation on peptide breakdown and ammonia production were determined by incubating unmodified and acetylated substrates with sheep rumen micro-organisms in vitro. Ammonia production from casein and lactalbumin was affected little by acetylation, but acetylation of the corresponding enzymic hydrolysates caused ammonia production to be more than halved after 3-6 h incubation. Estimation of peptides remaining in rumen fluid showed that the decreased ammonia production was a consequence of peptides being hydrolysed more slowly. Acetylated Ala-Ala, Ala-Ala-Ala (Ala3), Leu-Gly-Gly, Phe-Gly-Gly and Val-Gly-Ser-Glu survived incubation with rumen fluid in vitro for 6 h, whereas almost none of the corresponding unmodified peptides was present at 6 h. The protection afforded to larger pure peptides was less reliable: for example, 72% of acetylated bradykinin was hydrolysed after 1 h. N-Acetyl Ala3 had only a minor inhibitory effect on the breakdown of Ala3 and Ala4, suggesting that although acetyl peptides were broken down more slowly than unmodified peptides they did not inhibit peptidase activity.

Properties of ionophore-resistant Bacteroides ruminicola enriched by cultivation in the presence of tetronasin

Bacteroides ruminicola M384 was grown in the presence of increasing concentrations of tetronasin, an ionophore that has been developed as a feed additive for ruminants. The resulting culture, B. ruminicola M384/TnR, was then maintained in medium containing 0.1 microgram tetronasin/ml. Growth of the parent strain was eliminated by the addition of 0.1 micrograms tetronasin/ml, but the growth rate of B. ruminicola M384/TnR, which grew more slowly than the parent strain, was unaffected by adding tetronasin. Bacteroides ruminicola M384/TnR retained its resistance to tetronasin even after repeated subculture in the absence of the ionophore, suggesting that a mutation had occurred. The absence of plasmids in individual colonies of B. ruminicola M384/TnR implied that the mutation was chromosomal. Bacteroides ruminicola M384/TnR was also more resistant to the ionophores monensin and lasalocid and, to a lesser degree, to the antibiotic avoparcin than B. ruminicola M384. Binding of [14C]tetronasin to B. ruminicola M384/TnR was lower than binding of the ionophore to the parent stain, and this difference was eliminated by washing cells with EDTA. The peptidolytic activity of B. ruminicola M384 towards triphenylalanine (Mr = 460) was unaffected in B. ruminicola M384/TnR, but the rate of breakdown tetraphenylalanine (Mr = 607) was decreased. This difference was also abolished by EDTA. It was concluded that growth of B. ruminicola in the presence of tetronasin resulted in a mutation affecting the permeability of the cell envelope, such that permeation of tetronasin and molecules of a similar size (Mr = 628) was decreased.

Balancing carbohydrates and proteins for optimum rumen microbial yield

Establishing conditions under which rumen fermentation will be optimized requires an understanding of the nutrient requirements of the mixed microbial population. The major nutrients required by rumen microbes are carbohydrates and proteins, but the most suitable sources and quantities needed to support maximum growth have not been determined. Digestion of proteins results in the production of peptides, which can accumulate in the rumen. Peptides are further hydrolyzed to amino acids, some of which are deaminated, producing ammonia. Although peptides, amino acids, and ammonia all may individually serve as sources of N for various microbes, the total population achieves the highest growth rate on mixtures of all three sources. In a somewhat analogous manner, carbohydrates are digested by exoenzymes to oligosaccharides that are available for crossfeeding by the mixed microbial population. Based on data from both in vitro and in vivo studies, there is general agreement that rate of digestion of carbohydrates is the major factor controlling the energy available for microbial growth; in addition, rate of digestion of total carbohydrate is directly related to proportion of starches, pectins, and sugars. Proteins affect both total fermentation and production of microbial DM per unit of carbohydrate fermented. It appears that the quantity of ruminally available protein needed to optimize microbial growth may, under some conditions, be as high as 14 to 15% of diet DM.