Stimulatory effect of indole-3-acetic acid on aerial mycelium formation and antibiotic production in Streptomyces spp.

Abstract

An investigation was conducted to explore the effect of the phytohormone indole-3-acetic acid (IAA) on cellular differentiation in streptomycetes. A total of 21 Streptomyces strains known to produce antibiotics were tested. IAA (1–20 μg/ml) in Bennett’s agar markedly stimulated aerial mycelium formation and antibiotic production in 12 and 13 test strains, respectively. The stimulating effect of IAA was confirmed even in a submerged culture: production of an anthracycline group antibiotic, rhodomycin, by S. purpurascens NBRC 13077 cultured in oatmeal-MYM broth, was markedly enhanced by addition of IAA (20 μg/ml). mRNA differential display (RT-PCR) analysis revealed that expression of rdmA, rdmB, rdmC, rdmD and rdmE, all genes involved in rhodomycin production, was up-regulated by IAA treatment in S. purpurascens. These results suggest that IAA may act as a common regulating agent for sporulation and secondary metabolism in streptomycetes.