Incorporation of 15N and 14C into amino acids of bacterial and protozoal protein in the rumen of the cow on urea-rich feed

Abstract

Abstract. The utilization of the non-protein nitrogen and carbon of feed by rumen microorganisms for the synthesis of protein was studied by administering [U-14 C] sucrose and 15 NH 4 C1 to a cow on urea-rich, low-protein feed. By studying the labelling of the protozoa and bacteria and the amino acids isolated from them at intervals up to 48 hours afterwards, it was found that the bacteria synthesized amino acids from nonprotein nitrogen much more rapidly and effectively than the protozoa. Also the labelling of the carbon in the amino acids of the bacteria was more rapid than in the protozoa.In both protozoa and bacteria there was intracellular storage of [ l4 C] sucrose.Of the bacterial amino acids the most vigorous 14 C labelling was found in Glu, Arg, Lys, Val and Ala and the weakest labelling in Gly, His and Ser. Of the protozoal amino acids Ala, Asp, Glu, Leu and Lys had the highest labelling and Pro, Gly, His and Phe the lowest. In the bacterial protein the labelling of Pro and Arg was ten times that of the corresponding protozoal amino acids, and Asp, Ser and Ala four times.After the 15 NH 4 C1 dose the half-life of 15 N in the rumen fluid was estimated to be 3.3 h. Labelled ammonium nitrogen was about 11 -l5 % of the bacterial nitrogen and 2-3 % of the protozoal nitrogen after 1 h. Of the protozoal amino acids Ala, Glu, Val, Asp and Met had the most vigorous labelling, and of the bacterial amino acids Glu, Asp, Ser, He and Tyr. The slowest incorporation of ammonium nitrogen was into His, Pro, Arg and Gly in both bacteria and protozoa. The labelling of the bacterial amino acids was approximately 7 8 times more vigorous than that of the protozoal amino acids. The labelling of Ala was only 4 times, and that of Val, Met and Glu 5 times more vigorous than with protozoal protein. The pathway of histidine synthesis seemed to be restricted in both bacteria and protozoa and therefore may be a limiting factor in protein synthesis, particularly in cows fed urea as the sole source of nitrogen.Of the 14 C and 15 N label given, 12.9 and 9 % respectively was secreted in the milk during the first 3 days; over the same period the 14 C and 15 N excreted in the faeces plus urine accounted for 16.9 and 44.3 % respectively of that administered.

Studies on the nitrogen compounds of the faeces of dairy cows fed urea as the sole or partial source of nitrogen

“…In the faeces of 0-and ULP-cows the contents of glutamic acid, methionine, isoleucine and tyrosine were greater than with Nor P-cows, whereas the amounts of proline, glycine, histidine and arginine were smaller. In a feeding experiment with 15 NH 4 C1 the slowest incorporation of ammonium nitrogen was into histidine, proline, arginine and glycine with both bacteria and protozoa in the rumen of the ULP-cows (Syväoja and Kreula 1979). The amino acid composition of NorP-cows' faeces was almost the same as that in the studies of Tamminga (1975).…”

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

“…It should, however, be pointed out that in some experiments alanine accumulation was shown in Bacteriodes amylophilus which contained no detectable alanine dehydrogenase (Jenkinson et al 1979). Other investigators, using 15N-labelled urea or ammonium chloride to study ammonia incorporation into whole bacteria in vitro, have also found alanine to be one of the most highly labelled amino acids (Shimbayashi et al 1975;Syvaoja & Kreula, 1979). Salter et al (1979) found relatively high labelling of alanine in whole bacteria in vivo after adding 15N-labelled urea to the rumen and postulated that this was due to the action of transaminases, the amino group coming from glutamate or aspartate.…”

Rumen holotrich ciliate protozoa.

“…Mixed protozoal preparations containing holotrich ciliates have been used in studies on the nature and properties of rumen protozoal protease (96,187,(222)(223)(224) and metabolism of specific amino acids including lysine (190), tryptophan (95), arginine, proline, ornithine (196,198), citrulline (198), threonine (197), and methionine (160,197). Mixed populations have also been used to examine the range of anmino acids taken up (11,186), the factors affecting this incorporation (10, 120), and de novo amino acid synthesis (225,232). The rumen protozoal fraction has a range of transaminase activities (27, 28, 131) and will incorporate exogenous urea added to the culture medium (181).…”