Nitrogen Utilization and Metabolism in Ruminococcus albus 8

Abstract

The model rumen Firmicutes organism Ruminococcus albus 8 was grown using ammonia, urea, or peptides as the sole nitrogen source; growth was not observed with amino acids as the sole nitrogen source. Growth of R. albus 8 on ammonia and urea showed the same growth rate (0.08 h ؊1 ) and similar maximum cell densities (for ammonia, the optical density at 600 nm [OD 600 ] was 1.01; and for urea, the OD 600 was 0.99); however, growth on peptides resulted in a nearly identical growth rate (0.09 h ؊1 ) and a lower maximum cell density (OD 600 ‫؍‬ 0.58). To identify differences in gene expression and enzyme activities, the transcript abundances of 10 different genes involved in nitrogen metabolism and specific enzyme activities were analyzed by harvesting mRNA and crude protein from cells at the mid-and late exponential phases of growth on the different N sources. Transcript abundances and enzyme activities varied according to nitrogen source, ammonia concentration, and growth phase. Growth of R. albus 8 on ammonia and urea was similar, with the only observed difference being an increase in urease transcript abundance and enzyme activity in urea-grown cultures. Growth of R. albus 8 on peptides showed a different nitrogen metabolism pattern, with higher gene transcript abundance levels of gdhA, glnA, gltB, amtB, glnK, and ureC, as well as higher activities of glutamate dehydrogenase and urease. These results demonstrate that ammonia, urea, and peptides can all serve as nitrogen sources for R. albus and that nitrogen metabolism genes and enzyme activities of R. albus 8 are regulated by nitrogen source and the level of ammonia in the growth medium.A mmonia is the major end product of digestion of dietary protein and nonprotein nitrogen (urea and amino acids), as well as the major source of nitrogen for protein synthesis by ruminal bacteria (1-3). Results over a wide range of feed and N intakes demonstrate that 60 to 80% of bacterial N is derived from ammonia as a precursor (4). Since 14% of cell dry mass is nitrogen, bacterial protein synthesis and growth are greatly affected by the efficiency of ammonia assimilation. Despite its importance and central role as an intermediate in the degradation as well as assimilation of dietary nitrogen by intestinal bacteria, our understanding of the mechanism of ammonia assimilation in ruminal bacteria is superficial.Enzymes for assimilation of ammonia are widely conserved across the bacterial domain, with differences in distribution and transcriptional regulation influenced by environmental niche. Glutamate dehydrogenase (GDH), glutamine synthetase (GS), and glutamate synthase (GOGAT) are the three major types of enzymes that regulate the intracellular pool of nitrogen by controlling ammonia assimilation (5). GDH plays a significant role in the metabolism of nitrogen in many organisms by assimilating ammonia through the conversion of 2-oxoglutarate to glutamate. In the enteric proteobacteria, such as Escherichia coli and Salmonella, GDH is the primary nitrogen assimilation pathway when ...

Metabolic networks for nitrogen utilization in Prevotella ruminicola 23

“…4 ). In contrast to the enteric paradigm, our results demonstrate that P. ruminicola 23 utilizes the high substrate affinity GS–GOGAT enzymatic system to grow in non–limiting ammonium conditions, a pattern that has been also observed in Ruminococcus albus 8 18 . To our knowledge, this is the first description of an organism that uses both GDH and GS–GOGAT pathways for ammonium assimilation when grown under non–limiting concentrations of ammonium.…”

Maximizing efficiency of rumen microbial protein production

“…Although there seems to be little difference between AA and peptides for mixed cultures, many pure cultures of bacteria are stimulated by provision of small peptides rather than free AA (Wallace et al, 1997 ). For example, R. albus was shown to transport peptides but not AA (Kim et al, 2014 ). Peptides had a minor effect on this strain's growth rate, which was maximized at about 0.9/h.…”

“…Relative fluxes of these amination reactions depend on the Michaelis constant ( K m ) of ammonia for those enzymes but also based on transcription of ammonia-assimilating enzymes (Morrison and Mackie, 1997 ). Kim et al ( 2014 ) documented an excellent example of transcriptional control of ammonia-assimilating enzymes in R. albus . Although bacteria can make most of their AA, gelatin (which has a poor profile of Leu and the aromatic AA) decreased growth rates of mixed bacteria (Van Kessel and Russell, 1996 ) and increased energy spilling.…”

Amino Acids Metabolism in the Muscle of Sheep fed with Mitchell Grass Hay Supplemented with Gliricidia sepium

“…It was assumed that the spesific radioactivity (SRA) of leucine in the blood would start to plateau at two hours after the infusion started. Blood flow measurement was undertaken between the 3rd and 4th hour of L- [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]leucine infusion [20] by using 3 HOH (925 kBq/mL) solution that infused for 60 minutes into the right jugular venous catheter.…”

“…2 (2018) 75 -80 Atom Indonesia Journal homepage: http://aij.batan.go.id 0 amino acids needed for protein synthesis. The important of dietary nitrogen for ruminants is not only to supply amino acids, but also as nitrogen sources for microbial protein synthesised in the rumen [8,9]. Rumen microbial protein is also a contributor of amino acids for ruminant animals.…”