PRODUCTION AND REGULATION OF POTATO-SCAB-INDUCING PHYTOTOXINS BY STREPTOMYCES-SCABIES

Phytotoxins with potato-scab-inducing activity were produced by the pa thogenic Streptomyces scabies strain RB2 when grown on oatmeal agar me dium or in oatmeal broth medium. Five compounds isolated from cell fil trates were identified as thaxtomin compounds 1-5, previously reported as produced by S. scabies grown on potato slices. The optimum tempera ture for phytotoxin production in oatmeal broth medium was 28-degrees- C. Production of thaxtomin A, the major product, was repressed at leas t 130-fold when S. scabies RB2 was grown in oatmeal broth medium suppl emented with 0.5% glucose. Thaxtomin A production was also repressed b y tryptophan and tyrosine, precursors of which may be involved in feed back inhibition of early steps in biosynthesis. Phytotoxins were secre ted by the organism when the cells reached late exponential to early s tationary phases of culture growth. The time during growth at which ea ch thaxtomin compound was produced suggests a pathway for the latter s teps in thaxtomin biosynthesis.