In Vitro Production of Lysine from 2,2'-Diaminopimelic Acid by Rumen Protozoa

Rumen protozoa can produce lysine from free 2,2'-diaminopimelic acid (DAP). However, the quantitative importance of this transformation has been disputed; lysine contents of protozoal incubation supernatants reported by Onodera & Kandatsu [12] and Masson & Ling [9] show a 26-fold difference. The in vitro experimental methods of both groups were compared to determine the causes of this difference. Lysine production was proportional to DAP concentration. Results with rumen protozoa from sheep or goats were similar. The incubation medium and deproteinizing procedure of the Welsh group gave a two-fold increase in lysine production compared with Japanese protocols. Omissions of rice starch from protozoal incubations slightly increased lysine production, whereas omissions of antibacterial agents resulted in varying, yet relatively small changes. The greatest cause of the difference was the number of rumen protozoa incubated. When this factor was taken into account, the difference in the maximum rates of lysine production between the Welsh and Japanese groups was only three-fold, namely 4.5 versus 15.0 nmol lysine/10⁵ protozoa/h. Adding other amino acids to the incubations suggested that DAP uptake by rumen protozoa may occur via transport system ASC. The importance of DAP metabolism by protozoa as a source of lysine for ruminant host animals is discussed.