Abstract
The utilisation of a total of 20 amino acids by Eubacterium nodatum, a predominant asaccharolytic anaerobe isolated from human periodontal pockets, was studied. Washed cells of the microorganism produced substantial amounts of acetate, butyrate and ammonia from lysine, and butyrate and ammonia from arginine as main products under anaerobic conditions. They also produced a small amount of formate from histidine. Metabolic products were not detected from any of the other 17 amino acids. These results suggested that lysine and arginine were major substrates which E. nodatum could utilise. In fact, the growth of E. nodatum was markedly enhanced in the presence of lysine or arginine, but not by the other amino acids. Activities of arginine deiminase, ornithine carbamoyltransferase and carbamate kinase were found in the cell-free extract, suggesting that arginine was catabolised through the arginine deiminase pathway and ATP was formed in this pathway. Ornithine was further degraded to butyrate. In addition, the organisms produced arginine-carboxypeptidase, indicating that these bacteria may liberate C-terminal arginine from peptides and utilise it for their growth. Thus, E. nodatum may utilise lysine and arginine as major energy yielding substrates in human periodontal pockets.