Effect of hydrophobicity of utilization of peptides by ruminal bacteria in vitro

Amino acid utilization allows intestinal dominance of Lactobacillus amylovorus

The mammalian intestine harbors heterogeneous distribution of microbes among which specific taxa (e.g. Lactobacillus) dominate across mammals. Deterministic factors such as nutrient availability and utilization may affect microbial distributions. Due to physiological complexity, mechanisms linking nutrient utilization and the dominance of key taxa remain unclear. Lactobacillus amylovorus is a predominant species in the small intestine of pigs. Employing a pig model, we found that the small intestine was dominated by Lactobacillus and particularly L. amylovorus, and enriched with peptide-bound amino acids (PBAAs), all of which were further boosted after a peptide-rich diet. To investigate the bacterial growth dominance mechanism, a representative strain L. amylovorus S1 was isolated from the small intestine and anaerobically cultured in media with free amino acids or peptides as sole nitrogen sources. L. amylovorus S1 grew preferentially with peptide-rich rather than amino acid-rich substrates, as reflected by enhanced growth and PBAA utilization, and peptide transporter upregulations. Utilization of free amino acids (e.g. methionine, valine, lysine) and expressions of transporters and metabolic enzymes were enhanced simultaneously in peptide-rich substrate. Additionally, lactate was elevated in peptide-rich substrates while acetate in amino acid-rich substrates, indicating distinct metabolic patterns depending on substrate forms. These results suggest that an increased capability of utilizing PBAAs contributes to the dominance of L. amylovorus, indicating amino acid utilization as a deterministic factor affecting intestinal microbial distribution. These findings may provide new insights into the microbe-gut nutrition interplay and guidelines for dietary manipulations toward gut health especially small intestine health.

Amino Acid and Peptide Utilization Profiles of the Fluoroacetate-Degrading Bacterium Synergistetes Strain MFA1 Under Varying Conditions

Synergistetes strain MFA1 is an asaccharolytic ruminal bacterium isolated based on its ability to degrade fluoroacetate, a plant toxin. The amino acid and peptide requirements of the bacterium were investigated under different culturing conditions. The growth of strain MFA1 and its fluoroacetate degradation rate were enhanced by peptide-rich protein hydrolysates (tryptone and yeast extract) compared to casamino acid, an amino acid-rich protein hydrolysate. Complete utilization and preference for arginine, asparagine, glutamate, glycine, and histidine as free amino acids from yeast extract were observed, while the utilization of serine, threonine, and lysine in free form and peptide-bound glutamate was stimulated during growth on fluoroacetate. A predominant peptide in yeast extract preferentially utilized by strain MFA1 was partially characterized by high-liquid performance chromatography-mass spectrometry as a hepta-glutamate oligopeptide. Similar utilization profiles of amino acids were observed between the co-culture of strain MFA1 with Methanobrevibacter smithii without fluoroacetate and pure strain MFA1 culture with fluoroacetate. This suggests that growth of strain MFA1 could be enhanced by a reduction of hydrogen partial pressure as a result of hydrogen removal by a methanogen or reduction of fluoroacetate.

Effects of soybean small peptides on rumen fermentation and on intestinal and total tract digestion of luxi yellow cattle

Four Luxi beef cattle (400±10 kg) fitted with ruminal, duodenal and ileal cannulas were used in a 4×4 Latin square to assess the effects of soybean small peptide (SSP) infusion on rumen fermentation, diet digestion and flow of nutrient in the gastrointestinal tract. The ruminal infusion of SSP was 0 (control), 100, 200 and 300 g/d. Ruminal SSP infusion linearly (p<0.01) and quadratically (p<0.01) increased microbial protein synthesis and rumen ammonia-N concentration. Concentrations of total volatile fatty acid were linearly increased (p = 0.029) by infusion SSP. Rumen samples were obtained for analysis of microbial ecology by real-time PCR. Populations of rumen Butyrivibrio fibrisolvens, Streptococcus bovis, Ciliate protozoa, Ruminococcus flavefaciens, and Prevotella ruminicola were expressed as a proportion of total Rumen bacterial 16S ribosomal deoxyribonucleic acid (rDNA). Butyrivibrio fibrisolvens populations which related to total bacterial 16S rDNA were increased (p<0.05), while Streptococcus bovis populations were linearly (p = 0.049) and quadratically (p = 0.020) decreased by infusion of SSP. Apparent rumen digestibility of DM and NDF were (Q, p<0.05; L, p<0.05) increased with infusion SSP. Total tract digestion of DM, OM and NDF were linearly (p<0.01) and quadratically (p<0.01) increased by infusing SSP. The flow of total amino acids (AA), essential amino acids (EAA) and individual amino acids were linearly (p<0.01) and quadratically (p<0.01) increased with infusion SSP. The digestibility of Lysine was quadratically (p = 0.033) increased and apparent degradability of Arginine was linearly (p = 0.032) and quadratically (p = 0.042) increased with infusion SSP. The results indicated that infusion SSP could improve nutrient digestion, ruminal fermentation and AA availability.

Production of alkaline protease by Pseudomonas aeruginosa using proteinaceous solid waste generated from leather manufacturing industries

Animal fleshing (ANFL), the major proteinaceous solid waste discharged from leather manufacturing industries was used as the substrate for the production of alkaline protease by Pseudomonas aeruginosa. The strain isolated from the tannery wastewater was selected for its ability to produce protease of activity in the range 1160-1175 U ml(-1). The selective removal of non-fibrillar proteins such as albumin and globulin from ANFL by the protease enzyme during the progress of hydrolysis was confirmed using scanning electron microscopy (SEM). The breakdown of ANFL was also confirmed from the amino acid release into the fermentation medium by P. aeruginosa using high performance liquid chromatography (HPLC).

Effects of aromatic amino acids, phenylacetate and phenylpropionate on fermentation of xylan by the rumen anaerobic fungi, Neocallimastix frontalis and Piromyces communis

AIMS

Anaerobic fungi are important members of the fibrolytic community of the rumen. The aim of this study was to study their requirement for aromatic amino acids (AA) and related phenyl acids (phenylpropionic and phenylacetic acids) for optimal xylan fermentation.

METHODS AND RESULTS

Neocallimastix frontalis RE1 and Piromyces communis P were grown in a defined medium containing oat spelts xylan as the sole energy source, plus one of the following N sources: ammonia; ammonia plus a complete mixture of 20 AA commonly found in protein; ammonia plus complete AA mixture minus aromatic AA; ammonia plus phenyl acids; ammonia plus complete AA mixture without aromatic AA plus phenyl acids. Both species grew in all the media, indicating no absolute requirement for AA. The complete AA mixture increased (P<0.05) acetate concentration by 18% and 15%, sugar utilization by 33% and 22% and microbial yield by about 22% and 15% in N. frontalis and P. communis, respectively, in comparison with the treatments that had ammonia as the only N source. Neither the supply of aromatic AA or phenol acids, nor their deletion from the complete AA mixture, affected the fermentation rate, products or yield of either species.

CONCLUSIONS

AA were not essential for N. frontalis and P. communis, but their growth on xylan was stimulated. The effects could not be explained in terms of aromatic AA alone.

SIGNIFICANCE AND IMPACT OF THE STUDY

Ruminant diets should contain sufficient protein to sustain optimal fibre digestion by ruminal fungi. Aromatic AA or phenyl acids alone cannot replace the complete AA mixture.

Exposure of sheep scrapie brain homogenate to rumen-simulating conditions does not result in a reduction of PrPSclevels

AIMS

Experiments were designed to evaluate the potential of rumen-simulating conditions to reduce PrP(Sc) levels.

METHODS AND RESULTS

Scrapie-positive brain material was incubated under rumen-simulating conditions. Time points were taken over a 24-h period and PrP(Sc) levels were analysed by Western blot. No loss of PrP(Sc) was observed over a 24-h time period.

CONCLUSIONS

Our results indicate that a fully developed rumen fermentation does not provide significant protection against prion infection via the oral route. Developmental changes including senescence of immune system function or other developmental changes in the gastrointestinal tract are potential mechanisms by which relative bovine spongiform encephalopathy (BSE) susceptibility might vary with age.

SIGNIFICANCE AND IMPACT OF THE STUDY

Epidemiology of the BSE outbreak in the United Kingdom indicates that younger animals were at higher risk of infection. The rumen undergoes pronounced developmental changes early in life, coinciding with the introduction of fibre into the diet. The timeframe of highest risk of infection overlaps the time in life prior to full rumen development. This work indicates that a fully developed rumen does not provide significant protection against prion infection via the oral route of infection. This result implicates other developmental changes that are responsible for the age-dependent susceptibility of cattle to BSE.

Optimal protease production condition for Prevotella ruminicola 23 and characterization of its extracellular crude protease

In this study, Prevotella ruminicola 23 (ATCC 19189), a ruminal proteolytic bacterium, was used as protease producer to examine the optimal condition for protease production. The best carbon and nitrogen sources for the maximum growth were glucose with peptone. Both sucrose and glucose could stimulate high protease production. Casein and peptone are better nitrogen sources for protease production than other choice in this study. The best enzyme production condition was 18-20 h incubation which was at late log phase in the broth of 5% glucose or sucrose as carbon source with 0.1% ammonium chloride and 0.2% peptone as nitrogen sources. Most of the protease activity was secreted into broth (65%) and on cell surface (18%). The optimal temperature and pH for protease reaction were 40 degrees C and pH 6.8, respectively. After incubation for 6h, the crude extract maintained 50% of original protease activity at 30 and 50 degrees C, and protease activity was stable between pH 6 and 8. The protease inhibitor test showed that serine, aspartic acid and metallo-protease inhibitors could cause inhibition of proteolysis. Protein feedstuff degradation experiments suggested that protease in crude extract had higher degradation ability on fish meal, whey, and feather meal (2.39, 2.60 and 1.76 micromol aminoacid/mg enzyme/h) in comparison to soybean meal and blood meal (1.11 and 1.09 micromol aminoacid/mg enzyme/h). The protease in the crude extract should have application potential in term of improving utilization of fish meal and feather meal for monogastric animals.

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.

Mathematical estimations of hyper-ammonia producing ruminal bacteria and evidence for bacterial antagonism that decreases ruminal ammonia production(1)

Mixed ruminal bacteria (MRB) from cattle fed hay produced ammonia from protein hydrolysate twice as fast as MRB from cattle fed mostly grain, and a mathematical model indicated that cattle fed hay had approximately four-fold more hyper ammonia-producing ruminal bacteria (HAB). HAB had a high maximum velocity of ammonia production (V(max)) and low substrate affinity (high K(m)), but simulations indicated that only large changes in V(max) or K(m) would cause a large deviation in HAB numbers. Some carbohydrate-fermenting ruminal bacteria produced ammonia at a slow rate (CB-LA), but many of the isolates had almost no activity (CB-NA). The model indicated that the ratio of CB-LA to CB-NA had little impact on HAB numbers. Validations based on predicted ratios of HAB, CB-LA and CB-NA over-predicted the specific activity of ammonia production by MRB, but co-culture incubations indicated that washed MRB from cattle fed grain could inhibit HAB. Because autoclaved MRB had virtually no effect on HAB and the incubations were always carried out at pH 7.0, the inhibition was not simply a chemical effect (e.g. low pH).

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.

Copper metabolism of holstein and jersey cows and heifers fed diets high in cupric sulfate or copper proteinate

Eight Holstein and 8 Jersey primiparous cows (3 d postcalving) and 8 Holstein and 8 Jersey growing heifers were randomly assigned to 1 of 8 treatments in a 2 x 2 x 2 factorial arrangement to compare Cu metabolism between Holsteins and Jerseys and the bioavailabilities of Cu in Cu proteinate and CuSO4. The variables were Holstein or Jersey, Cu supplementation at 5 or 80 mg/kg of DM, and supplements of CuSO4 or Cu proteinate. Jerseys had higher hepatic Cu concentrations than did Holsteins on d 60 (346 vs. 303 micrograms/g of DM). At the high Cu supplementation, hepatic Cu increased more rapidly, and content was higher in Jerseys than in Holsteins by d 60 (520 vs. 439 micrograms/g of DM). On d 0, plasma Cu concentrations were 0.99 and 0.80 microgram/ml, and, on d 60, concentrations were 0.96 and 0.88 microgram/ml for Jerseys and Holsteins, respectively. Overall, serum ceruloplasmin oxidase activity was greater for Jerseys than for Holsteins. Jersey cows and heifers also had greater hepatic Fe (208 vs. 173 micrograms/g of DM) and lower hepatic Zn (82 vs. 91 micrograms/g of DM) than did Holstein cows and heifers at d 60. The bioavailability of Cu in Cu proteinate and CuSO4 was the same. Plasma Cu concentration and ceruloplasmin have limited value as indicators of Cu status and availability to dairy cows and heifers.

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.

In vitro ruminal degradation and synthesis of protein on fractions extracted from alfalfa hay and silage

Net release of degraded N as NH3 and total AA plus microbial protein synthesis, quantified from incorporation of 15NH3 into microbial protein, was used to estimate the rate and extent of in vitro degradation of protein fractions isolated from alfalfa hay and silage. Seven proteins (casein, alfalfa hay, alfalfa silage, extracts from alfalfa hay and silage, and residues from alfalfa hay and silage) were studied. Results from (NH4)2SO4 and SDS-PAGE fractionations suggested that soluble proteins in alfalfa hay and silage differed in susceptibility to proteolytic attack. Although the net release of NH3 plus total AA N from alfalfa silage and alfalfa silage extract was twofold greater than that from alfalfa hay and alfalfa hay extract, net microbial protein synthesis on alfalfa hay and alfalfa hay extract was 33 and 43% greater. Despite greater NPN content in alfalfa silage, protein degradation rate and estimated escape were similar for intact alfalfa hay (0.103/h and 43%) and silage (0.067/h and 43%). This result might be explained by the less efficient microbial utilization of silage NPN, greater protozoal numbers on hay, greater soluble true protein in hay, or differences in molecular mass and stability of soluble proteins in hay versus silage. Use of a two-compartment model, based on water-soluble and insoluble CP fractions assumed to pass with the liquid and solid phases, respectively, yielded RUP estimates for alfalfa hay and silage that were similar to NRC estimates.

An rRNA approach for assessing the role of obligate amino acid-fermenting bacteria in ruminal amino acid deamination

Ruminal amino acid degradation is a nutritionally wasteful process that produces excess ruminal ammonia. Monensin inhibited the growth of monensin-sensitive, obligate amino acid-fermenting bacteria and decreased the ruminal ammonia concentrations of cattle. 16S rRNA probes indicated that monensin inhibited the growth of Peptostreptococcus anaerobius and Clostridium sticklandii in the rumen. Clostridium aminophilum was monensin sensitive in vitro, but C. aminophilum persisted in the rumen after monensin was added to the diet. An in vitro culture system was developed to assess the competition of C. aminophilum, P. anaerobius, and C. sticklandii with predominant ruminal bacteria (PRB). PRB were isolated from a 10(8) dilution of ruminal fluid and maintained as a mixed population with a mixture of carbohydrates. PRB did not hybridize with the probes to C. aminophilum, P. anaerobius, or C. sticklandii. PRB deaminated Trypticase in continuous culture, but the addition of C. aminophilum, P. anaerobius, and C. sticklandii caused a more-than-twofold increase in the steady-state concentration of ammonia. C. aminophilum, P. anaerobius, and C. sticklandii accounted for less than 5% of the total 16S rRNA and microbial protein. Monensin eliminated P. anaerobius and C. sticklandii from continuous cultures, but it could not inhibit C. aminophilum. The monensin resistance of C. aminophilum was a growth rate-dependent, inoculum size-independent phenomenon that could not be maintained in batch culture. On the basis of these results, we concluded that the feed additive monensin cannot entirely counteract the wasteful amino acid deamination of obligate amino acid-fermenting ruminal bacteria.

Duodenal flow of microbial and feed nitrogen in sheep fed normal soybean meal or soybean meal treated with modified zein

The effect of protecting soybean meal from microbial degradation in the rumen on duodenal flow of microbial N and feed N was studied with sheep. The soybean meal was protected with chemically modified zein. Two groups of four wethers, each equipped with a ruminal cannula and a duodenal reentrant cannula, were fed a diet based on corn silage (1 kg of DM/d) that contained either a normal or protected soybean meal supplement. The results showed no appreciable differences between the two supplements in ruminal fluid pH, total N, and NAN concentrations; however, the concentration of total VFA was lower for protected soybean meal than for normal soybean meal. Although the flow of NAN into the duodenum was not affected, bacterial N flow was 18% lower, and feed N flow was 195% higher, for protected soybean meal than for normal soybean meal. The digestibilities of OM, ADF, and N in the digestive tract were not affected by the type of supplement. The treatment of soybean meal decreased the degradability of total feed N in the stomach by 22 percentage points, but the increased supply of feed N into the small intestine because of the treatment was at the expense of decreased bacterial synthesis of protein in the rumen, probably because of a shortage of RDP in the diet.

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.

Prediction of protein degradation of forages from solubility fractions

Two experiments were conducted to determine the relationship between enzymatic digestion of forage protein and fractionation based on solubility. The first experiment used 42 forages, each replicated three times, including different species, stages of maturity, and methods of conservation. Crude protein was fractionated into six parts for each forage by sequential extraction in TCA, bicarbonate-phosphate buffer, acetone, detergent at pH 7, and detergent with acid. Multiple regression analysis, with all the solubility fractions as independent variables, resulted in prediction of CP degradation by ruminal enzyme extract at 2 and 24 h; R2 were .88 and .81, respectively. Greater solubility in the buffer and the detergent at pH 7 was associated with higher protein degradation; solubility in acetone, detergent with acid, and insolubility were associated with lower degradation. In the second experiment, eight forages each replicated twice were digested with ruminal enzyme for 0, 2, 6, and 24 h and then were extracted as described. Solubility in TCA and acetone increased during degradation, but solubility in buffer, detergent with acid, and insolubility decreased. For both experiments, buffer-soluble CP was the only uniform fraction across forages; other fractions contained proteins that degraded at diverse rates. Solubility of CP is related to degradation properties, but further research is needed to improve the accuracy of predictions based on solubility.

The in vitro uptake and metabolism of peptides and amino acids by five species of rumen bacteria

Streptococcus bovis JB1, Prevotella ruminicola B(1)4, Selenomonas ruminantium Z108, Fibrobacter succinogenes S85 and Anaerovibrio lipolytica 5S were incubated with either 14C-peptides (mol. wt, 200-1000) or 14C-amino acids to compare their rates of uptake and metabolism. In experiment 1, the bacteria were grown and incubated in a complex medium, but no uptake of 14C-labelled substrates occurred. When casein digest was omitted, uptake rates of 14C-peptides were different (P < 0.01) with each species, but nil for 14C-amino acids. In experiment 2, to minimize the effects of non-radiolabelled peptides and amino acids, defined and semi-defined media were used. Patterns of 14C-peptide uptake resembled those of experiment 1. The 5-min rate for Strep. bovis JB1 was almost twice that of P. ruminicola B(1)4, though by 15 min they were similar and threefold greater than other species; that of A. lipolytica 5S was especially low. Incubations with 14C-amino acids resulted in a wide range (P < 0.01) of uptake rates; after 5 min P. ruminicola B(1)4 possessed the lowest and Strep. bovis JB1 the highest, but after 15 min, that of Sel. ruminantium Z108 was even higher. All bacteria, with the exception of P. ruminicola B(1)4, assimilated 14C-amino acids faster (P < 0.01) than 14C-peptides. Only Strep. bovis JB1 and P. ruminicola B(1)4 were capable of extensively metabolizing 14C-peptides, but all five species metabolized 14C-amino acids; there was evidence of substantial degradation and some synthesis. Calculations suggest that peptides could supply up to 43%, and amino acids 62% of the N requirements of rumen bacteria.

Supplemental protein influences on carbohydrate degradation and bacterial 16S ribosomal ribonucleic acid

This research examined the mechanism by which soybean protein stimulates growth of mixed ruminal anaerobes and degrades structural polysaccharides in vitro. Soybean meal, isolated soy protein, or branched-chain VFA was added to orchardgrass hay substrate in Experiment 1. Cell-wall degradation increased 14.5% over that of the control by protein addition. Protein addition resulted in 1.3- to 1.5-fold increases in bacterial growth. Hybridization with a 16S probe specific for Fibrobacter succinogenes indicated that protein addition did not influence the proportion of this species. For in vitro Experiment 2, optimal protein for cell-wall degradation was 2 g/L in cultures containing tall fescue hay. To determine whether protein stimulated microbial colonization of plant cell wall (Experiment 3), orchardgrass hay was placed in 14-L fermentors; treatments were control, NH3 N (2 g of N/L), or isolated soy protein (2 g of N/L). Addition of protein and NH3 N increased the extent of cell-wall disappearance 9.7% above control. Protein and ammonia improved cell-wall digestion, but protein had the greatest stimulatory effect on prokaryote growth with no preferential effect of F. succinogenes.

Effect of monensin on the specific activity of ammonia production by ruminal bacteria and disappearance of amino nitrogen from the rumen

When unadapted mixed ruminal bacteria (312 mg of protein per liter) were treated with monensin (5 mM) in vitro, the rates of ammonia production from enzymatic digests of casein, gelatin, and soy protein (0.5 g of N per liter) were decreased from 46 +/- 2 to 24 +/- 1, 20 +/- 1 to 7 +/- 1, and 40 +/- 2 to 18 +/- 2 nmol/mg of protein per min, respectively. Monensin also caused a decrease in ammonia production in vivo. Nonlactating dairy cows which were fed 0.56 kg of timothy hay 12 times per day had a steady-state ruminal ammonia concentration of 2.7 +/- 0.1 mM, and the ammonia concentration decreased to 1.2 +/- 0.2 mM when monensin (350 mg/day) was added to the diet. The decrease in ammonia production was associated with a 10-fold reduction (4.1 x 10(6) versus 4.2 x 10(5)/ml) in the most probable number of ammonia-producing ruminal bacteria that could use protein hydrolysate as an energy source. Monensin had little effect on the most probable number of carbohydrate-utilizing ruminal bacteria (6.5 versus 7.0 x 10(8)/ml). The addition of protein hydrolysates (560 g) to the rumen caused a rapid increase in the ammonia concentration, but this increase was at least 30% lower when the animals were fed monensin.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Nutrient requirements versus supply in the dairy cow: strategies to account for variability

Dairy producers must overcome substantial challenges to achieve milk outputs > 14,000 kg of milk/yr per cow within the next decade. To obtain high productivity, a more complete comprehension of the dynamics of metabolism, nutrient utilization, and nutrient absorption will enable better prediction of the efficiency of utilization of these nutrients. A better understanding of the dynamics of rumen function and a more accurate prediction of nutrient flow from the rumen are necessary. Grouping strategy and group feeding behavior influence cow productivity and farm profitability. Understanding of the variance of individual cow responses to management practice is critical. Feeding system design and management and diet formulation techniques need to be developed that recognize the dynamic nature of cow physiology and the variability in feedstuffs and cow requirements. These concepts need to be integrated into total farm management and require the use of new computer modeling technologies.

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.

Recent developments in gastrointestinal absorption and tissue utilization of peptides: a review

Considerable evidence has been accumulated regarding the absorption of dipeptides and tripeptides, yet, even with the growing body of knowledge, the nutritional and metabolic significance of peptide absorption is not fully understood, especially in ruminants. Muscle, mammary gland, liver, kidney, intestinal mucosa, and other tissues either have been shown to have, or are suspected to have, the ability to utilize peptides as a source of AA to meet cellular demands. Investigations suggest that ruminal microbes have the ability to produce substantial amounts of small peptides as a consequence of their hydrolysis of dietary proteins. The extent to which intact peptides may be absorbed into the blood is controversial. Some of the inconsistency in reported observations may be because of limitations of analytical procedures, species differences, or both. Peptide absorption appears to be an important physiological process in ruminants and may constitute the primary source of absorbed AA. The recent observation that the stomach region of the gastrointestinal tract may be an important site of peptide absorption is highly significant. Emerging evidence for the contribution that peptide absorption makes to AA provisioning of ruminants may change some of the currently held views about protein utilization in these unique animals.

Resistance of proline-containing peptides to ruminal degradation in vitro

Mixed ruminal bacteria utilized an enzymatic digest of casein at a rate faster than that for an enzymatic digest of gelatin, but neither amino acid source was completely utilized even when the incubation period was as long as 96 h. Since the reaction of ninhydrin with the residual nonammonia, nonprotein nitrogen was more than twofold stronger when the samples were hydrolyzed with 6 N HCl, it appeared that much of the residual nitrogen was from peptides. Approximately 66% of the nonammonia, nonprotein, ninhydrin-reactive material could not be recovered as amino acids, but there was a significant decrease in total amino acid nitrogen when the samples were pretreated with a C18 Sep-Pak column to remove peptides. The resistant peptides had an abundance of proline, and subsequent incubations showed that synthetic dipeptides which contained proline were hydrolyzed slowly. Lysine appears to be the amino acid which is most apt to limit ruminant production. Dipeptides containing proline and lysine were hydrolyzed at least fivefold slower than lysine-alanine. Methionine, another potentially limiting amino acid, was also degraded at a slower (2.5-fold) rate when it was present as part of a proline dipeptide.

The breakdown and utilization of peptides by strains of Fusobacterium nucleatum

It has been claimed that most strains of Fusobacterium nucleatum require peptides rather than free amino acids for growth. In contrast, we have shown that, under continuous culture conditions, all strains tested grow in a chemically defined medium (CDM). The purposes of this study were to determine whether resting cells of F. nucleatum could attack unsubstituted peptides and whether growing cells could utilize a peptide fraction prepared from a commercial peptone. Resting cells cleaved all 19 peptides, containing 3-6 residues, and the 4 key energy-yielding amino acids--Glu, His, Ser and Lys--were rapidly taken up. A hydrophilic Casitone fraction, rich in Glu, promoted growth and peptides < 1 kDa were rapidly utilized. The cleaved residues metabolized were those previously shown to limit growth in CDM: Glu, Ser, His and Lys. The endopeptidase activities of Porphyromonas gingivalis would provide the necessary peptides for the growth of F. nucleatum, which may partly explain why these two organisms frequently coexist in periodontally diseased sites.

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.

Influence of hydrophobicity on oligopeptide utilization by oral streptococci

The growth responses of Streptococcus mutans VA-29R, Streptococcus sanguis ATCC 10556, and Streptococcus mitior NIH to hydrophilic and hydrophobic peptides obtained following isopropanol fractionation of Trypticase were compared. Although the two fractions contained peptides of similar molecular size, differences were observed with respect to amino acid compositions. S. mutans VA-29R showed a pronounced difference in growth response to hydrophilic vs. hydrophobic peptides. While growth of this micro-organism on hydrophilic peptides was indistinguishable from that on unfractionated Trypticase, only very slow growth occurred on the hydrophobic peptides. S. sanguis ATCC 10556 and S. mitior NIH also displayed some selectivity, as evidenced by their faster relative growth rates on hydrophilic, as compared with hydrophobic, peptides. The results of this study support the conclusion that the properties of the substrate, as defined by its amino acid composition, may be more important than molecular size as a factor influencing recognition and subsequent utilization of oligopeptides as sources of amino acids for growth by these three oral streptococci.

Analysis of peptide metabolism by ruminal microorganisms

Methods were developed for the determination of oligoalanine and other short-chain peptides and peptide analogs in ruminal fluid by using reverse-phase high-pressure liquid chromatography. Chromatographic analysis of the breakdown of (Ala)3 and (Ala)4 in ruminal fluid in vitro revealed that the predominant mechanism of hydrolysis was a dipeptidyl peptidase-like activity. Hydrolysis proceeded from the N terminal of the peptide chain; N-acetyl-(Ala)3 was broken down at 11% of the rate of breakdown of (Ala)3 or (Ala)3-p-nitroanilide. (Ala)2-p-nitroanilide was hydrolyzed most rapidly of the arylamide substrates tested, but fluorogenic 4-methoxy-2-naphthylamide (MNA) compounds were more convenient and potentially more versatile substrates than p-nitroanilides. Gly-Arg-MNA was the most rapidly hydrolyzed dipeptidyl peptidase substrate, suggesting that ruminal peptidase activity was predominantly of a type I specificity.

Transport of glutamine by Streptococcus bovis and conversion of glutamine to pyroglutamic acid and ammonia

Streptococcus bovis JB1 cells energized with glucose transported glutamine at a rate of 7 nmol/mg of protein per min at a pH of 5.0 to 7.5; sodium had little effect on the transport rate. Because valinomycin-treated cells loaded with K and diluted into Na (pH 6.5) to create an artificial delta psi took up little glutamine, it appeared that transport was driven by phosphate-bond energy rather than proton motive force. The kinetics of glutamine transport by glucose-energized cells were biphasic, and it appeared that facilitated diffusion was also involved, particularly at high glutamine concentrations. Glucose-depleted cultures took up glutamine and produced ammonia, but the rate of transport per unit of glutamine (V/S) by nonenergized cells was at least 1,000-fold less than the V/S by glucose-energized cells. Glutamine was converted to pyroglutamate and ammonia by a pathway that did not involve a glutaminase reaction or glutamate production. No ammonia production from pyroglutamate was detected. S. bovis was unable to take up glutamate, but intracellular glutamate concentrations were as high as 7 mM. Glutamate was produced from ammonia via a glutamate dehydrogenase reaction. Cells contained high concentrations of 2-oxoglutarate and NADPH that inhibited glutamate deamination and favored glutamate formation. Since the carbon skeleton of glutamine was lost as pyroglutamate, glutamate formation occurred at the expense of glucose. Arginine deamination is often used as a taxonomic tool in classifying streptococci, and it had generally been assumed that other amino acids could not be fermented. To our knowledge, this is the first report of glutamine conversion to pyroglutamate and ammonia in streptococci.

The importance of the form of nitrogen on microbial protein synthesis in the rumen of cattle receiving grass silage and continuous intrarumen infusions of sucrose

1. In a 4 x 4 Latin square design experiment, four cattle were given grass silage in two meals per d to satisfy maintenance energy requirements. In addition, sucrose (170 g/kg silage dry matter (DM] was infused intraruminally at a constant rate with no nitrogen supplementation; with the infusion intraruminally of either casein (23 g/kg silage DM) or urea (8 g/kg silage DM); or with soya-bean meal (64 g/kg silage DM) fed in two equal portions. 2. Samples of duodenal digesta representative of a 24 h period were obtained using chromium-EDTA and ytterbium acetate for flow estimation and 35S as a marker of microbial N entering the small intestine. Samples of rumen fluid were also taken for estimation of rumen pH and concentrations of ammonia-N and volatile fatty acids. Estimates of apparent organic matter (OM) and N digestibility and of the rates of silage DM and N disappearance from porous synthetic-fibre bags incubated in the rumen were also made. 3. The N supplements had no significant effects on rumen pH, concentrations of volatile fatty acids, their molar proportions or the disappearance of DM or N from porous synthetic-fibre bags. N supplementation increased rumen ammonia-N concentrations (urea, P less than 0.05; casein, soya-bean meal, not significant). 4. N supplementation had no significant effects on the digestion of OM, acid-detergent fibre or soluble carbohydrate. 5. Infusion of casein increased the quantities of total non-ammonia-N (not significant) and microbial N (P less than 0.05) entering the small intestine daily and the efficiency of rumen microbial N synthesis (not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Fermentation of peptides and amino acids by a monensin-sensitive ruminal Peptostreptococcus

A monensin-sensitive ruminal peptostreptococcus was able to grow rapidly (growth rate of 0.5/h) on an enzymatic hydrolysate of casein, but less than 23% of the amino acid nitrogen was ever utilized. When an acid hydrolysate was substituted for the enzymatic digest, more than 31% of the nitrogen was converted to ammonia and cell protein. Coculture experiments and synergisms with peptide-degrading strains of Bacteroides ruminicola and Streptococcus bovis indicated that the peptostreptococcus was unable to transport certain peptides or hydrolyze them extracellularly. Leucine, serine, phenylalanine, threonine, and glutamine were deaminated at rates of 349, 258, 102, 95, and 91 nmol/mg of protein per min, respectively. Deamination rates for some other amino acids were increased when the amino acids were provided as pairs of oxidized and reduced amino acids (Stickland reactions), but these rates were still less than 80 nmol/mg of protein per min. In continuous culture (dilution rate of 0.1/h), bacterial dry matter and ammonia production decreased dramatically at a pH of less than 6.0. When dilution rates were increased from 0.08 to 0.32/h (pH 7.0), ammonia production increased while production of bacterial dry matter and protein decreased. These rather peculiar kinetics resulted in a slightly negative estimate of maintenance energy and could not be explained by a change in fermentation products. Approximately 80% of the cell dry matter was protein. When corrections were made for cell composition, the yield of ATP was higher than the theoretical maximum value. It is possible that mechanisms other than substrate-level phosphorylation contributed to the energetics of growth.

Sodium-dependent transport of neutral amino acids by whole cells and membrane vesicles of Streptococcus bovis, a ruminal bacterium

Streptococcus bovis JB1 cells were able to transport serine, threonine, or alanine, but only when they were incubated in sodium buffers. If glucose-energized cells were washed in potassium phosphate and suspended in potassium phosphate buffer, there was no detectable uptake. Cells deenergized with 2-deoxyglucose and incubated in sodium phosphate buffer were still able to transport serine, and this result indicated that the chemical sodium gradient was capable of driving transport. However, when the deenergized cells were treated with valinomycin and diluted into sodium phosphate to create both an artificial membrane potential and a chemical sodium gradient, rates of serine uptake were fivefold greater than in cells having only a sodium gradient. If deenergized cells were preloaded with sodium (no membrane potential or sodium gradient), there was little serine transport. Nigericin and monensin, ionophores capable of reversing sodium gradients across membranes, strongly inhibited sodium-dependent uptake of the three amino acids. Membrane vesicles loaded with potassium and diluted into either lithium or choline chloride were unable to transport serine, but rapid uptake was evident if sodium chloride was added to the assay mixture. Serine transport had an extremely poor affinity for sodium, and more than 30 mM was needed for half-maximal rates of uptake. Serine transport was inhibited by an excess of threonine, but an excess of alanine had little effect. Results indicated that S. bovis had separate sodium symport systems for serine or threonine and alanine, and either the membrane potential or chemical sodium gradient could drive uptake.