An Investigation of Regulatory Mechanisms of A-500359s Production in Mutants Isolated from Streptomyces griseus SANK 60196

The nucleoside antibiotic A-500359s are produced by Streptomyces griseus SANK 60196. During a screening program of A-500359s high-producing strains, several interesting mutants were isolated and classified into three groups according to two characteristics, spore-forming ability and the retention of a giant linear plasmid SGF180, as follows: [spore+ SGF180-], [bald SGF180+] and [bald SGF180-]. A-500359s production was markedly decreased in all the mutants [spore+ SGF180-] and completely lacking in all the bald-type mutants. To understand the regulatory mechanisms of A-500359s production in these mutants, co-cultivation analyses were conducted in several mutant combinations, and the effect of an addition of an EtOAc extract, which was prepared from a culture broth of an A-500359s producer, was tested. A-500359s production was clearly restored when mutant [spore+ SGF180-] was co-cultivated with mutant [bald SGF180+] and the A-500359s production of the mutant [bald SGF180+] was activated by the addition of an EtOAc extract. The results suggested that SGF180 plays an important role in A-500359s production and that A-500359s biosynthesis might be controlled by a low molecular weight compound, such as an A-factor-like compound, synthesized by the product of afsA gene that was lost in all the tested bald-type mutants.