Differences in the Utilization of Glycerol and Glucose by Mycobacterium phlei

A basic difference was found in the kinetics of uptake and utilization of glucose and glycerol by washed suspensions of Mycobacterium phlei. With glucose, the rates of uptake, respiration, and assimilation were saturated at low external substrate concentration. With glycerol, these rates were found to increase with increasing substrate concentration and did not show saturation at any concentration tested. Qualitatively similar patterns were observed for cells grown on either glycerol or glucose. Above a saturation concentration, ratios of cell (14)C to CO(2) (14)C for uniformly labeled (14)C-glucose were constant at a value of 0.96. Glycerol-U-(14)C, on the other hand, yielded cell-(14)C/CO(2)-(14)C ratios which were highest at the lowest glycerol concentration tested, and decreased with increasing substrate concentration. The distribution of the glucose and glycerol carbons assimilated into M. phlei were qualitatively similar. Quantitatively, however, the uptake and assimilation of glycerol was far more rapid than that of glucose for all substrate concentrations employed. These quantitative differences in the utilization of glycerol and glucose could account for the increased content of nonessential lipid and polysaccharide found in glycerol-grown M. phlei.