Selection of Streptomyces ambofaciens mutants that produce large quantities of spiramycin and determination of optimal conditions for spiramycin production.

The aim of this work was to develop a strategy to isolate a morphologically stable mutant of Streptomyces ambofaciens ATCC 15154 which produced high titers of spiramycin. The rationale was to grow a nitrosoguanidine-mutated population for many generations under nonselective conditions followed by two cycles of protoplast formation and regeneration. A total of 2,400 surviving colonies were then screened for spiramycin production and subsequently checked for stability. From this experiment, strain 6-37 was isolated that produced 181 mg of spiramycin per liter and only one morphological type. The parent strain (ATCC 15154) produced 107 mg of spiramycin per liter and four morphological types. Strain 6-37 was then mutated with nitrosoguanidine, and 14,000 colonies were screened for spiramycin production. From this experiment, five strains were isolated that produced titers ranging from 187 to 373 mg of spiramycin per liter. Subsequent media and time studies with these strains resulted in a fermentation that produced 1,728 mg of spiramycin per liter.