CAULOBACTER-CRESCENTUS MUTANT DEFECTIVE IN MEMBRANE PHOSPHOLIPID-SYNTHESIS

To study the relationship between phospholipid synthesis and organelle biogenesis in the dimorphic bacterium C. crescentus, auxotrophs were isolated which require exogenous glycerol or glycerol 3-phosphate for growth when glucose is used as the C source. Upon glycerol deprivation, net phospholipid synthesis ceased immediately in a glycerol 3-phosphate auxotroph which had levels of biosynthetic sn-glycerol 3-phosphate dehydrogenase (EC 1.1.1.8) activity 10 times lower than that of the wild type. In the absence of glycerol, optical density of the culture continued to increase for the equivalent of 1 generation, although the cells did not divide. After the equivalent of 1 generation time, rapid cell death occurred. Cell death occurred when phospholipid synthesis was inhibited by cerulenin. Although RNA and protein syntheses continued at a reduced rate for the equivalent of 1 generation in mutant strains, a substantial decrease in rate of DNA synthesis occurred immediately upon glycerol deprivation. Revertant strains had wild-type levels of glycerol 3-phosphate dehydrogenase activity and normal rates of phospholipid and macromolecular synthesis.