Optimization of culture conditions for indole-3-pyruvic acid production by Streptomyces griseoflavus

Thirty strains of actinomycetes were isolated from fertile soils in Egypt on starch–nitrate agar. The isolated organisms were recognized as spore formers with aerial mycelia containing L-DAP (diaminopimelic acid) and glycine. The inability of the vegetative mycelia to fragment into bacillary or coccoid forms and the presence of spores borne on sporophores, placed these organisms in the family Streptomycetaceae. The isolates also proved to be aerobic and Gram positive. The absence of DL-DAP and the presence of L-DAP in their cell hydrolysates, and the production of a wide range of pigments in the aerial and substrate mycelia, assigned these isolates to the genus Streptomyces. The isolated organisms were screened for production of plant growth regulators, and the most active producer of indole-3-pyruvic acid was examined further. Using the described morphological, physiological, and biochemical criteria for identification, this organism was identified as Streptomyces griseoflavus. The optimal culture conditions for maximal production of both cellular and extracellular indole-3-pyruvic acid by S. griseoflavus were investigated and shown to be as follows: a culture medium composed of (g∙100 mL−1) NH4NO3, 0.55; DL-tryptophan, 0.4; NaCl, 0.7; at pH 7 (buffered); with an incubation period of 6 days at 28 °C in the dark and under shaking conditions.Key words: actinomycetes, plant growth regulators, Streptomyces griseoflavus, indole-3-pyruvic acid, culture conditions.