Citrate formation in Mycobacterium phlei.

Although it is well known that citrate stimulates the growth of acid fast bacteria, the metabolic role of citrate is still obscure in this bacterial group. Washed suspensions of mycobacteria either fail to oxidize citrate or oxidize this substance slowly (Edson, 1951). On the other hand, clarified extracts of mycobacteria oxidize citrate to a-ketoglutarate (Geronimus, Gray, and Birkeland, 1949; Faine, Whiteside, and Edson, 1951). These facts suggest that citric acid may play its conventional part in a Krebs cycle. Lactate, pyruvate, and acetate are readily oxidized by the nonproliferating cells of many species of mycobacteria which will also utilize these compounds as sole sources of carbon when growth takes place in a synthetic medium (Edson and Hunter, 1943; Franke and Schillinger, 1944). In the case of Mycobacterium phlei an acetone powder and soluble extracts prepared from it will oxidize lactate to acetate and carbon dioxide (Edson, 1947). Acetate is formed also from pyruvate (Lindsay, O'Donnell, and Edson, 1950), but no information has been obtained regarding the pathway for the ultimate oxidation of acetate. The ability of mycobacteria to oxidize intermediates of the citric acid cycle (Edson and Hunter, 1943, 1947; Franke and Schillinger, 1944; Geronimus, Gray, and Birkeland, 1949) suggests that acetate may be metabolized via this catalytic mechanism. Hence the problem has been investigated by studying the formation of citrate in preparations made from M. phlei.