l-Glutamine regulates amino acid utilization by intestinal bacteria
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Catabolism of amino acids (AA) by intestinal bacteria greatly affects their bioavailability in the systemic circulation and the health of animals and humans. This study tests the novel hypothesis that l-glutamine regulates AA utilization by luminal bacteria of the small intestine. Pure bacterial strains (Streptococcus sp., Escherichia coli and Klebsiella sp.) and mixed bacterial cultures derived from the jejunum or ileum of pigs were cultured in the presence of 0–5 mM l-glutamine under anaerobic conditions. After 3 h of incubation, samples were taken for the determination of AA utilization. Results showed concentration-dependent increases in the utilization of glutamine in parallel with the increased conversion of glutamine into glutamate in all the bacteria. Complete utilization of asparagine, aspartate and serine was observed in pure bacterial strains after the 3-h incubation. The addition of glutamine reduced the net utilization of asparagine by both jejunal and ileal mixed bacteria. Net utilization of lysine, leucine, valine, ornithine and serine by jejunal or ileal mixed bacteria decreased with the addition of glutamine in a concentration-dependent manner. Collectively, glutamine dynamically modulates the bacterial metabolism of the arginine family of AA as well as the serine and aspartate families of AA and reduced the catabolism of most AA (including nutritionally essential and nonessential AA) in jejunal or ileal mixed bacteria. The beneficial effects of glutamine on gut nutrition and health may involve initiation of the signaling pathways related to AA metabolism in the luminal bacteria of the small intestine.
KeywordsAmino acids Gut bacteria Small intestine Nutrition Swine
Colony forming unit
Nutritionally essential amino acid
This work was supported by the Natural Science Foundation of China (30810103909), the National Basic Research Program of China (2004CB117500-4), and Texas AgriLife Research Hatch Project (H-8200). We are grateful to Dr. J. Fleming, Dr. H. J. Gao, and Dr. J. J. Wang for technical assistance and helpful discussion. Z.-L. Dai thanks the China Scholarship Council for support of his study at Texas A&M University between 17 February 2009 and 28 February 2010.
Conflict of interest
The authors declare that they have no conflict of interest.
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