Biophysical optima for metabolism of Mycobacterium leprae

The metabolic response of freshly harvested, nude-mouse-derived Mycobacterium leprae to biophysical parameters was studied to facilitate an understanding of axenic culture requirements. Quantitation of intracellular ATP and the rate of [U-14C]palmitic acid incorporation into phenolic glycolipid I (PGL-I) were used as metabolic indicators after axenic incubation in modified Dubos medium under various biophysical conditions. PGL-I synthesis was optimal at 33 degrees C, whereas ATP was optimally maintained at less than or equal to 33 degrees C. Both metabolic indices showed sharp reductions at 37 degrees C. After 5 days of incubation, PGL-I synthesis and ATP maintenance showed pH optima of 5.1 to 5.6, with the higher value appearing optimal for ATP maintenance after extended incubation. Metabolic activity was negatively affected by strong reducing agents, and ATP maintenance was optimal when the gaseous environment was maintained at 2.5 to 10% oxygen. The results may partially explain the failure to cultivate the leprosy bacillus in vitro.