Effect of antibiotics on formation of aerial mycelium and production of phytotoxins in Streptomyces spp

Thirty different antibiotics with various structures and modes of action were tested for effects on the formation of aerial mycelia in Streptomyces scabies, S. acidiscabies, and S. alboniger. Many antibiotics inhibiting protein synthesis suppressed the development of aerial mycelia at less than 10% of the concentration required for growth inhibition in substrate mycelia. Spectinomycin selectively prevented aerial mycelium formation without inhibiting substate mycelia in all strains tested. Chlortetracycline inhibited aerial mycelium formation in the pathogens causing potato scab, S. scabies and S. acidiscabies, but was ineffective in S. alboniger. In the two pathogenic strains, inhibition of aerial mycelia by spectinomycin and chlortetracycline decreased phytotoxin production substantially.