A scotochromogenic slow-growing mycobacterium probably the etiologic agent of rat leprosy.

Pioneering in the metabolism of noncultivable mycobacteria , Gray ( 5), Hanks (6), and Hanks and Gray ( 8) searched systematically for s u bst ra te s as prospective e ne rgy sources for M. leprae (MI) and M. lepraemurium (Mlm). After several years of investigations , they concluded that MI and Mlm cannot derive energy from substrates which cultivable mycobacteria use as energy sources for growth, multiplication and expression of virulence. It was advocated, and quite generally accepted, that both of these mycobacteria are metabolically deficient and depend on the host to supply most of the necessary molecule s to build up their cellular constituents. This view was supported by the findings by many investigators that MI and Mlm are deficient in enzymes which play an important if not key role in energy metaboli sm and respiration. Most of the studies were made with Mlm because these cells are readily available in large quantities from infected rats. It was reported that a key enzyme of the tricarboxylic acid cycle, a-ketoglutaric dehydrogenase, is absent in Mlm, that they also have low NADH oxidase activity and that cytochrome c is absent in these cells ( IX. 19 ). In contrast to these findings , we advocated the antipode of this often accepted concept. We have shown that at least Mlm is metabolically competent, having a complete functional tricarboxylic acid cycle and a wellfunctioning uninterrupted electron transport chain; cytochrome c included (1 0. 16 ). With improved methods, we have shown the presence of a-ketoglutarate dehydrogenase, NADH oxidase and cytochrome c in Mlm. Our investigations clearly showed that host grown Mlm can oxidize at least four groups of substrates. One is complex, heat stable: yeast extract. The other is succininc acid, and