Production of thaxtomin A by Streptomyces scabies strains in plant extract containing media

Thaxtomin A production by Streptomyces scabies is induced by plant extracts in culture media. We compared the production of thaxtomin A by three Streptomyces scabies strains (EF-35, CG1, and ATCC 49173) in different culture media in a first attempt to identify the plant molecules required for the biosynthesis of thaxtomin A. Thaxtomin A production varied greatly among media and among S. scabies strains. Strain CGI presented a higher production than the other strains in all complex media. Oat bran broth is the best thaxtomin A production medium, and suberin is the only plant polymer allowing the production of thaxtomin A in minimal medium. The three S. scabies strains had extracellular esterase activities when grown in the presence of potato suberin or oat bran. We suggest that extracellular esterases allow the release from lipid polymers of plant molecules that may act as inducers for thaxtomin A biosynthesis genes or as precursors in the biosynthetic pathway of thaxtomin A.