Ammonia metabolism in rumen bacteria and mucosa from sheep fed soy protein or urea

Effects of L-glutamine supplementation on degradation rate and rumen fermentation characteristics in vitro

Objective

Two follow-up studies (exp. 1 and 2) were conducted to determine the effects of L-glutamine (L-Gln) supplementation on degradation and rumen fermentation characteristics in vitro.

Methods

First, rumen liquor from three cannulated cows was used to test L-Gln (50 mM) degradation rate and ammonia-N production at 6, 12, 24, 36, and 48 h after incubation (exp. 1). Second, rumen liquor from two cannulated steers was used to assess the effects of five levels of L-Gln including 0% (control), 0.5%, 1%, 2%, and 3% at 0, 3, 6, 12, 24, 36, and 48 h after incubation on fermentation characteristics, gas production, and degradability of nutrients (exp. 2).

Results

In exp. 1, L-Gln degradation rate and ammonia-N concentrations increased over time (p<0.001). In exp. 2, pH was reduced significantly as incubation time elapsed (p<0.001). Total gas production tended to increase in all groups as incubation time increased. Acetate and propionate tended to increase by increasing glutamine (Gln) levels, whereas levels of total volatile fatty acids (VFAs) were the highest in 0.5% and 3% Gln groups (p<0.001). The branched-chain VFA showed both linear and quadratic effects showing the lowest values in the 1% Gln group particularly after 6 h incubation (p<0.001). L-Gln increased crude protein degradability (p<0.001), showing the highest degradability in the 0.5% Gln group regardless of incubation time (p<0.05). Degradability of acid detergent fiber and neutral detergent fiber showed a similar pattern showing the highest values in 0.5% Gln group (p<0.10).

Conclusion

Although L-Gln showed no toxicity when it was supplemented at high dosages (2% to 3% of DM), 0.5% L-Gln demonstrated the positive effects on main factors including VFAs production in-vitro. The results of this study need to be verified in further in-vivo study.

Ammonia and urea transport across the rumen epithelium: a review

The transport of nitrogen across the rumen epithelium is characterized by absorption of ammonia from the rumen and by an influx of urea into the rumen. The transport rates of both compounds are large and exhibit wide variation. The transport of ammonia occurs in two forms: in the lipophilic form as NH3, the magnitude of which is linearly related to the pH in the ruminal fluid at pH values above 7, while at a physiological pH of 6.5 or lower, ammonia is predominantly absorbed as NH4+via putative potassium channels in the apical membrane. The uptake of NH4+depends on the potential difference of the apical membrane, Pda, and shows competition with K uptake. The pathway for basolateral exit of NH4+is unknown. Hence, the relative transport rates of NH3or NH4+are determined by the ruminal pH according to the Henderson–Hasselbalch equation. Transport of ammonia interacts with the transport of Na and Mg mainly via changes of the intracellular pH. Urea recycling into the rumen has been known for many years and the transport across the rumen epithelium is mediated via urea transporters in the luminal and basolateral membrane of the epithelium. Transport of urea occurs by simple diffusion, but is highly variable. A significant increase of urea influx is caused by the fermentation products CO2and short-chain fatty acids. Conversely, there is some evidence of inhibition of urea influx by ruminal ammonia. The underlying mechanisms of this modulation of urea transport are unknown, but of considerable nutritional importance, and future research should be directed to this aspect of ruminal transport.

Splanchnic metabolism of nutrients and hormones in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera1,2,3

Effects of increased ammonia and/or arginine absorption on net splanchnic (portal-drained viscera [PDV] plus liver) metabolism of nonnitrogenous nutrients and hormones in cattle were examined. Six Hereford x Angus steers (501 +/- 1 kg BW) prepared with vascular catheters for measurements of net flux across the splanchnic bed were fed a 75% alfalfa:25% (as-fed basis) corn and soybean meal diet (0.523 MJ of ME/[kg BW(0.75).d]) every 2 h without (27.0 g of N/kg of DM) and with 20 g of urea/kg of DM (35.7 g of N/kg of DM) in a split-plot design. Net flux measurements were made immediately before and after a 72-h mesenteric vein infusion of L-arginine (15 mmol/h). There were no treatment effects on PDV or hepatic O2 consumption. Dietary urea had no effect on splanchnic metabolism of glucose or L-lactate, but arginine infusion decreased net hepatic removal of L-lactate when urea was fed (P < 0.01). Net PDV appearance of n-butyrate was increased by arginine infusion (P < 0.07), and both dietary urea (P < 0.09) and arginine infusion (P < 0.05) increased net hepatic removal of n-butyrate. Dietary urea also increased total splanchnic acetate output (P < 0.06), tended to increase arterial glucagon concentration (P < 0.11), and decreased arterial ST concentration (P < 0.03). Arginine infusion increased arterial concentration (P < 0.07) and net PDV release (P < 0.10) and tended to increase hepatic removal (P < 0.11) of insulin, as well as arterial concentration (P < 0.01) and total splanchnic output (P < 0.01) of glucagon. Despite changes in splanchnic N metabolism, increased ammonia and arginine absorption had little measurable effect on splanchnic metabolism of glucose and other nonnitrogenous components of splanchnic energy metabolism.

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.

Arginase distribution in tissues of domestic animals

1. A new colorimetric method was used for determination of arginase in different tissues of some domestic animals. 2. In all species studied liver was the richest source of arginase. 3. Significant differences were observed in the specific activity of arginase in livers from different species. 4. In all species, besides liver, kidney and brain also contained significant levels of arginase. 5. In the dog, in addition to the three organs mentioned above, lung, heart, spleen and skeletal muscle showed some arginase activity. 6. In sheep and cattle significant arginase activity was observed in the rumen. No differences were observed between epithelial and muscular layers of different parts of digestive system in all species studied. 7. These results are discussed in terms of the possible role of arginase in different tissues of animals.

The ecology and pathogenicity of urease-producing bacteria in the urinary tract

Urease activity is a physiological function of many bacteria that enables these organisms to utilize urea as a source of nitrogen. The association of ureolytic bacteria with human or animal hosts varies widely from a commensal relationship as demonstrated with skin microflora, a symbiotic relationship in the gastrointestinal tract, to a pathogenic relationship in the urinary tract. Since similar or identical species of bacteria such as Staphylococcus aureus are found in all three environments, the effect of urease activity on the host must be solely a function of the environment of these organisms. In this review, the importance of urease to bacteria is discussed, identifying the gastrointestinal tract as a major reservoir of ureolytic bacteria and investigating the urinary tract environment and the infectious struvite stone production that often accompanies urease-producing bacteria there. Finally, an infection model is presented which explains the development and growth of these urinary calculi and their remarkable persistence in spite of modern urological treatments.

Chemical factors involved in ruminal fiber digestion

In the United States, cattle are commonly fed diets containing cereal grains. The presence of starch and sugars reduces fiber digestion, which may in turn depress intake. In this paper, chemical constraints that may be responsible for the decrease in fiber digestion are explored. A major factor appears to be rumen pH. Moderate depression in pH, to approximately 6.0, results in a small decrease in fiber digestion, but numbers of fibrolytic organisms are usually not affected. Further decreases to 5.5 or 5.0 result in depressed growth rates and decreased fibrolytic microbes, and fiber digestion may be completely inhibited. Proliferation of organisms on readily fermentable carbohydrates may increase the need for total nitrogen as both ammonia and amino acids. The value of amino acids to cellulolytic organisms appears to be primarily as sources of isobutyric, isovaleric, and 2-methylbutyric acids. This reinforces the need to establish dietary requirements for nonprotein nitrogen, degradable protein, and isoacids. Other factors affecting fiber digestion, such as inhibition of cellulytic enzymes and plant concentrations of lignins and phenyl propanoids, are also discussed.

Glutamine synthetase activity in the ruminal bacterium Succinivibrio dextrinosolvens

Succinivibrio dextrinosolvens C18 was found to possess glutamine synthetase (GS), urease, glutamate dehydrogenase, and several other nitrogen assimilation enzymes. When grown in continuous culture under ammonia limitation, both GS and urease activities were high and glutamate dehydrogenase activity was low, but the opposite activity pattern was observed for growth in the presence of ample ammonia. The addition of high-level (15 mM) ammonium chloride to ammonia-limited cultures resulted in a rapid loss of GS activity as measured by either the gamma-glutamyl transferase or forward assay method with cells or extracts. No similar activity losses occurred for urease, glutamate dehydrogenase, or pyruvate kinase. The GS activity loss was not prevented by the addition of chloramphenicol and rifampin. The GS activity could be recovered by washing or incubating cells in buffer or by the addition of snake venom phosphodiesterase to cell extracts. Manganese inhibited the GS activity (forward assay) of untreated cells but stimulated the GS activity in ammonia-treated cells. Alanine, glycine, and possibly serine were inhibitory to GS activity. Optimal pH values for GS activity were 7.3 and 7.4 for the forward and gamma-glutamyl transferase assays, respectively. The glutamate dehydrogenase activity was NADPH linked and optimal in the presence of KCl. The data are consistent with an adenylylation-deadenylylation control mechanism for GS activity in S. dextrinosolvens, and the GS pathway is a major route for ammonia assimilation under low environmental ammonia levels. The rapid regulation of the ATP-requiring GS activity may be of ecological importance to this strictly anaerobic ruminal bacterium.

Interaction between nickel and protein source in the ruminant

Eighty growing steers were used to determine the effect of nickel supplementation on performance and metabolic parameters of steers fed corn silage-based diets supplemented with different crude protein sources. Crude protein sources examined included: (1) soybean meal, (2) blood meal, (3) urea, and (4) blood meal-urea (two-thirds of supplemental nitrogen from blood meal and one-third from urea). The protein sources differed in ruminal degradability, nitrogen solubility, and nickel content. Nickel was added within each protein treatment to supply either 0 or 5 ppm of supplemental nickel. The experiment was 84 d in duration and rumen fluid and blood samples were collected on days 42 and 80. Average daily gain and feed efficiency were not affected by nickel supplementation. The addition of 5 ppm supplemental nickel greatly increased rumen bacterial urease activity regardless of protein source. When samples were collected prior to feeding on day 80, nickel increased serum urea nitrogen concentrations in steers fed urea, but decreased circulating urea concentrations in animals fed blood meal or the blood meal-urea combination.Ad libitum intake of trace mineral salt was greatly reduced in steers receiving 5 ppm supplemental nickel. The present study suggests that the source of protein may influence ruminant responses to dietary nickel.

Microbial ecology and activities in the rumen: part 1

This review describes the progress which has been made during the last 10 to 15 years in the field of rumen microbiology. It is basically an account of new discoveries in the bacteriology, protozoology, biochemistry, and ecology of the rumen microbial population. As such it covers a wide range of subjects including the isolation and properties of methanogenic bacteria, the role of rumen phycomycete fungi, anaerobic energy conservation, and general metabolic aspects of rumen microorganisms. It also attempts, however, to describe and develop new concepts in rumen microbiology. These consist principally of interactions of the microbemicrobe, microbe-food and microbe-host types, and represent the main areas of recent advance in our understanding of the rumen ecosystem. The development of experimental techniques such as chemostat culture and scanning electron microscopy are shown to have been instrumental in progress in these areas. The paper is concluded with an assessment of our present knowledge of the rumen fermentation, based on the degree of success of experiments with gnotobiotic ruminants inoculated with defined flora and in mathematical modeling of the fermentation. The efficacy of chemical manipulation of the fermentation in ruminant is also discussed in this light.

Distribution and changes in urease (EC 3.5.1.5) activity in Rumen Simulation Technique (Rusitec)

1. The Rumen Simulation Technique (Rusitec) was used in a series of long-term experiments to study the distribution and changes of urease (EC 3.5.1.5) activity in a heterogeneous fermentation system. 2. It was shown that in Rusitec the high urease activity from the inoculum decreased to low values, that the rate of decrease was consistent with simple dilution of ureolytic micro-organisms and that the urease activity could be restored to original values by infusion of urea into the reaction vessels. The magnitude of this urease activity was a direct function of the amounts of urea infused. Single daily additions of the same or greater amounts of urea in food or as solid failed to increase the urease activity significantly. 3. In general, urease activity increased 2-6 h after feeding and the increases were greater with roughage diets. 4. The ureolytic activity per unit volume was always higher in compartment 2(space occupied by micro-organisms that are loosely associated with the solid) than in compartment 1 (strained rumen contents) or compartment 3 (space occupied by microbial population that cannot be washed out of the solid matrix). 5. The distribution of urease activity between the compartments was different from the distribution of certain other enzymes (e.g. protease and alkaline phosphatase (EC 3.1.3.1)). 6. Apart from the boundary region, the concentrations of urease, ammonia and volatile fatty acids in compartment 2 were constant, while the concentrations of protein, DNA and another enzyme (alkaline phosphatase) increased with the depth of the compartment. Specific urease activity (per unit weight of protein or DNA) was much higher in compartment 1 than in compartment 2 and it decreased markedly with depth of compartment. 7. The concentrations of ammonia were always much higher in the solid matrix (compartments 2 and 3) than in the free suspension of micro-organisms (compartment 1). There was a linear relation between these two quantities. 8. The results are discussed in relation to published work on the entry and metabolism of urea in the rumen.

Regulation of urease and ammonia assimilatory enzymes in Selenomonas ruminantium

Urease and glutamine synthetase activities in Selenomonas ruminantium strain D were highest in cells grown in ammonia-limited, linear-growth cultures or when certain compounds other than ammonia served as the nitrogen source and limited the growth rate in batch cultures. Glutamate dehydrogenase activity was highest during glucose (energy)-limited growth or when ammonia was not growth limiting. A positive correlation (R = 0.96) between glutamine synthetase and urease activities was observed for a variety of growth conditions, and both enzyme activities were simultaneously repressed when excess ammonia was added to ammonia-limited, linear-growth cultures. The glutamate analog methionine sulfoximine (MSX), inhibited glutamine synthetase activity in vitro, but glutamate dehydrogenase, glutamate synthase, and urease activities were not affected. The addition of MSX (0.1 to 100 mM) to cultures growing with 20 mM ammonia resulted in growth rate inhibition that was dependent upon the concentration of MSX and was overcome by glutamine addition. Urease activity in MSX-inhibited cultures was increased significantly, suggesting that ammonia was not the direct repressor of urease activity. In ammonia-limited, linear-growth cultures, MSX addition resulted in growth inhibition, a decrease in GS activity, and an increase in urease activity. These results are discussed with respect to the importance of glutamine synthetase and glutamate dehydrogenase for ammonia assimilation under different growth conditions and the relationship of these enzymes to urease.

Ammonia saturation constants for predominant species of rumen bacteria

Ammonia saturation constants were determined for representative pure cultures of predominant, anaerobic, fermentative rumen bacteria. Based on growth experiments with ammonia limited continuous cultures, average estimates for ammonia saturation constants of Bacteroides amylophillus and Bacteroides ruminicola were 10.5 and 23.5 microM ammonia-nitrogen, respectively. With ammonia-limited linear-growth cultures, the estimates for the ammonia saturation constants of B. amylophilus, B. ruminicola, and Selenomonas ruminantium were, respectively, 6, 33.5, and 18 microM ammonia nitrogen. By a third method, which involved estimation of ammonia concentration in the medium when the growth rate of ammonia-limited batch cultures reached half maximal, the ammonia saturation constant was determined for the species mentioned as well as Megaspaera elsdenii and Ruminococcus flavefaciens. Except for M. elsdenii, saturation constants of the other bacteria were less than 50 microM ammonia nitrogen. An organism with a saturation constant for ammonia of 50 microM growing in a medium containing 1 mM ammonia should achieve 95% of its maximum specific growth rate. Many of the predominant species of rumen bacteria are efficient scavengers of ammonia.

Ammonia anabolizing enzymes in cattle and buffalo fed varied nonprotein nitrogen and carbohydrates

Adult male fistulated crossbred cattle and buffalo, four each, were on rations with rations of nonprotein nitrogen to carbohydrates of 1:45, 1:37.5, and 1:30 and a control of no urea in a 4 x 4 Latin square switchover design. The influence of various test diets on enzymes assimilating ruminal ammonia was elucidated to find an optimum ratio of nonprotein nitrogen to soluble carbohydrates for efficient utilization of dietary nitrogen. Inclusion of urea in graded amounts in the ration induced activities of amino-stransferases. Specific activities of trans-aminases were higher in cattle and buffalo for rations with ratios of 1:45 and 1:30 compared to control and 1:37.5 (nonprotein nitrogen to carbohydrate ratio). This indicates a better adaptation of rumen microbes on two former rations which did not differ in augmentation of enzyme activities. Peak enzyme activity of cattle and buffalo at 2 h postfeeding did not differ for microbial enzymes. The ration with narrowest nonprotein nitrogen and carbohydrate ratio (1:30) may be optimum for microbial synthesis of amino acid. It will be worthwhile to study whether a still narrower ratio can make feeding of ruminants more economical.

Ammonia assimilation and glutamate formation in the anaerobe Selenomonas ruminantium

Selenomonas ruminantium was found to possess two pathways for NH4+ assimilation that resulted in net glutamate synthesis. One pathway fixed NH4+ through the action of an NADPH-linked glutamate dehydrogenase (GDH). Maximal GDH activity required KCl (about 0.48 M), but a variety of monovalent salts could replace KCl. Complete substrate saturation of the enzyme by NH4+ did not occur, and apparent Km values of 6.7 and 23 mM were estimated. Also, an NADH-linked GDH activity was observed but was not stimulated by KCl. Cells grown in media containing non-growth-rate-limiting concentrations of NH4+ had the highest levels of GDH activity. The second pathway fixed NH4+ into the amide of glutamine by an ATP-dependent glutamine synthetase (GS). The GS did not display gamma-glutamyl transferase activity, and no evidence for an adenylylation/deadenylylation control mechanism was detected. GS activity was highest in cells grown under nitrogen limitation. Net glutamate synthesis from glutamine was effected by glutamate synthase activity (GOGAT). The GOGAT activity was reductant dependent, and maximal activity occurred with dithionite-reduced methyl viologen as the source of electrons, although NADPH or NADH could partially replace this artificial donor system. Flavin adenine dinucleotide, flavin mononucleotide, or ferredoxin could not replace methyl viologen. GOGAT activity was maximal in cells grown with NH4+ as sole nitrogen source and decreased in media containing Casamino Acids.

An independent microbial flora of the epithelium and its role in the ecomicrobiology of the rumen

IT has been suggested that the bacterial flora of the rumen should be considered as three distinct, interacting populations-the bacteria of rumen fluid (the population which has been studied most extensively), the bacteria associated with food particles, and the bacteria adhering to the epithelial wall of the organ(1). Until now, studies of the 'epithelial' population have been restricted to examination of postmortem samples of wall tissue and its attached bacterial flora(2-5). A recently developed technique(6) for feeding young sheep for long periods solely by infusion of protein and other essential nutrients into the abomasum, and of volatile fatty acids and bicarbonate buffer into the rumen, has provided us with an opportunity to study in isolation the role of the bacterial population of the wall in the ecomicrobiology of the rumen in the living animal. Our studies show that this population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue. Furthermore, our results point to an inverse relationship between ammonia concentration and ureolytic activity in rumen fluid, which may account for the control which ammonia exerts over flux of urea across the rumen wall(7-9).

Microbial transaminase activities and their relationship with bovine rumen metabolites

Two each adult male crossbred cattle and murrah buffalo were fed a diet of alfalfa hay, chopped wheat straw, and concentrate mixture. Total rumen transaminase activity of cattle was higher than that of buffalo. Rumen protozoal fractions showed higher total transaminase activity than bacterial fractions in both ruminant species. Besides generally studied glutamate oxalacetate transaminase and glutamate pyruvate transaminase, a large number of other microbial transaminases also have been detected in the rumen of both the ruminant species. Bacterial fractions of rumen liquor were devoid of transaminases utilizing tryptophan, threonine, and lysine as their substrates. Ruminal ammonia and nonprotein nitrogen were correlated positively with microbial transaminases in both species. Transamination reactions may be important for assimilation of ruminal ammonia to cellular proteins.

Rumen bacterial urease requirement for nickel

Lambs were fed a basal purified diet low in nickel (60 ppb) or the basal diet supplemented with 5 ppm of nickel to determine if rumen bacterial urease was a nickel-requiring enzyme. Two collection periods with lambs fed a diet in which all the nitrogen was supplied as preformed protein (casein) indicated that ruminal urease activity was much lower in lambs fed the low nickel diet. When 1% urea was added to the basal diet, urease activity increased slightly with both treatments; however, bacterial urease activity was still much higher in the lambs receiving 5 ppm of nickel. Ruminal volatile fatty acids were not influenced by dietary nickel. Ruminal urease requires nickel for maximal activity.

The effect of dietary content of plant protein on the utilization of urea in the bovine rumen

1. Four young Friesian bulls with rumen fistulas were given four isocaloric all-concentrate diets containing different amounts and sources of nitrogen in a Latin square arrangement. Diet HP (high-protein) contained 2·31% plant nitrogen; diet MPU (medium-protein with urea) 1·67% plant nitrogen and 0·69% urea nitrogen (total 2·36%); diet LPU (low-protein with urea) 0·95% plant nitrogen and 0·69% urea nitrogen (total 1·65%); diet HPU (high-protein with urea) 2·28% plant nitrogen and 0·69% urea nitrogen (total 2·97%), calculated on an air-dry basis.

2. The rumen pH varied between 5·8 and 6·1 with diets HP, MPU and HPU, but was significantly lower with diet LPU with values between 5·4 and 5·8.

3. The results showed no differences between the isonitrogenous diets HP and MPU except that replacement of plant nitrogen with urea was followed by an increase in the concentration of ammonia in the rumen. With the diets containing urea, the concentrations of rumen ammonia varied inversely with the amount of dietary plant nitrogen supplied, indicating a negative effect of plant nitrogen on urea utilization.

4. Concentrations of alkali-labile nitrogen (amide) were not increased with diets containing urea except with diet HPU, which produced the highest concentrations of ammonia in the rumen.

5. The concentration of true protein in the rumen and the amino acid distribution were similar with all four diets, indicating the ability of the microflora to adapt to qualitative and quantitative differences in dietary nitrogen intake.

6. Ration acceptability was lower with diets LPU and HPU than with diets HP and MPU.

7. Large differences between individual animals in rumen pH, percentage of dry matter and total nitrogen concentration in the rumen were noted.