Incorporation of nitrogen into rumen bacterial fractions of steers given protein- and urea-containing diets. Ammonia assimilation into intracellular bacterial amino acids

Abstract

1. Experiments were carried out in vivo to investigate the pathways of ammonia incorporation into rumen bacteria, bacterial fractions and free amino acids within the bacteria.2. Steers were alternately given two isoenergetic, isonitrogenous diets containing the nitrogen mainly as either urea or decorticated groundnut meal (DCGM). At the end of each period on a given diet, a solution of l5NH,C1 was infused into the rumen and samples of rumen contents were removed at 2, 10, 20 and 90 min and 5, 10 and 24 h afterwards. Concentrations of ammonia and its 16N enrichment were determined and samples of mixed rumen bacteria were prepared. Bacteria were disrupted ultrasonically and separated into bacterial protein, cell wall and protein-free cell supernatant fractions. Amino acids were separated after hydrolysis and their 15N contents determined.3. A rumen fluid circulation pump was developed so that representative samples could be taken at very short time intervals after the introduction of the 15N label.4. Rumen pH changes, rumen fluid dilution rates and patterns of rumen ammonia concentrations were consistent with normal rumen metabolism. Net bacterial synthesis (as calculated from the net outflow of bacteria from the rumen) was significantly (P < 0.05) greater with the DCGM diet (12.4 g bacterial N/d) than with the urea diet (9.24 g bacterial N/d).5. With both diets the 16N label rapidly left the rumen ammonia pool and entered the rumen bacteria. Analysis of the bacterial fractions indicated that the label appeared rapidly in the protein-free cell supernatant fraction and more slowly in the bacterial protein and cell wall fractions.6. With the DCGM diet bacteria apparently utilized intracellular label less efficiently than with the urea diet. The proportion of N in the protein-free cell supernatant was higher with the DCGM diet, suggesting increased levels of intracellular amino acids and peptides, following extracellular protein degradation.7. Levels of enrichment of the amino acids alanine and glutamate in the protein-free cell supernatant fraction suggested that the enzymes alanine dehydrogenase (EC 1 .4.1.1) and glutamate dehydrogenase (EC 1 . 4 . 1 . 2 and 1 .4.1.4) may be the major enzymes for assimilating ammonia when concentrations of soluble carbohydrate and rumen ammonia are high in the rumen.8. The high levels of intracellular alanine are discussed with reference to published work on the excretion of alanine by rumen bacteria.

Ammonia and amino acids modulates enzymes associated with ammonia assimilation pathway by ruminal microbiota in vitro

“…The response of GDH to AA supplementation, probably for the same reasons discussed above for GS. The ADH is another major enzyme involved in ammonia assimilation, and forms alanine by amination of pyruvate, under conditions of excess soluble carbohydrate and rumen ammonia (Blake et al, 1983). Alanine, serine and NADPH could inhibit the aminating reaction of this enzyme, but ammonia could induce ADH (Aharonowitz and Friedrich, 1980).…”

Influence de la nature de la source azotée (tourteau d'arachide ou urée) sur l'activité microbienne mesurée in vitro

“…Our results suggest that nitrogen from groundnut meal is used more efficiently by rumen microbes than urea, which agrees with growth trials conducted simultaneously on bulls.Certains travaux ont montré que la synthèse microbienne était plus importante à partir d'acides aminés provenant de protéines dégradables que de l'ammoniaque issue d'azote uréique (Blake et al, 1983 …”

“…Certains travaux ont montré que la synthèse microbienne était plus importante à partir d'acides aminés provenant de protéines dégradables que de l'ammoniaque issue d'azote uréique (Blake et al, 1983 …”

Supplemental protein sources for growing cattle fed corn stover silage

“…reported that a deficiency of methionine and phenylalanine may limit bacterial growth on dieta low in protein and high in RPR. Similarly, Blake et al (1983) found that net bacterial #ynth##i# waa aignifioantly greater vith a natural protein source than with urea diets.…”

“…Amino groupa are then tranaferred to other auitable carbon akeletona for the formation of AA which together with preformed compounda, are uaed in protein and nucleic acid ayntheaia. The eozymee required for the firat atagea of euch a echeme have all been identified in mixed rumen bacteria (Falmquist and Baldwin, 1966;Chalupa et al, 1970;Brfle et al, 1977;Blake et al, 1983) and a variety of aechaniama, acme following established pathway# and others uaing less common routes, h*ve been identified ss providing the carbon ekelet<m# for AA synthesis (Allison, 1969;Emmanuel and Nillgan, 1972;Kristensen, 1974;Bauer et al, 1975).…”