BALD MUTANTS OF STREPTOMYCES-GRISEUS THAT PREMATURELY UNDERGO KEY EVENTS OF SPORULATION

To identify the structural defects of nonsporulating mutants of Strept omyces griseus, the wild-type strain and class III bald mutants were e xamined by using transmission electron microscopy, ultrasonic treatmen t, and fluorescence microscopy after the induction of submerged sporul ation by phosphate starvation. In the wild-type strain, submerged spor ulation was marked by the relatively synchronous formation of sporogen ic hyphae, nucleoid segregation, deposition of sporulation septa, and subsequent thickening of the spore walls during maturation, All of the class III mutants prematurely synthesized sporulation septa and thick spore walls, The class IIIA and C mutants formed sporogenic hyphae ea rlier than the wild-type strain and underwent nucleoid segregation in parallel with sporulation septum formation, In the class IIIB (bldA) m utant, DNA segregation appeared to be uncoupled from septum formation, The results indicate that the class III mutants are defective in loci that are involved in the regulation of key events of Streptomyces mor phogenesis.