Effect of some culture conditions on the production of indole-3-acetic acid and a gibberellin-like substance by Azotobacter vinelandii

Ethyl acetate extracts of concentrated culture supernatants were studied using thin-layer and paper chromatography in four solvent systems and Avena, Lactuca, and Hordeum bioassays. Indole-3-acetic acid (IAA) was synthesized between 3 and 6 days of incubation and remained maximal at 8 × 10−8 M from 7 to 40 days. A possible precursor, tentatively identified as 3-indoleacetamide (IAM), was present during the early period of IAA production. Relatively more IAA was produced in shaking than in stationary culture and in nitrogen-free than in ammonium-containing medium.A gibberellin-like substance which had some similarity to GA3 was detected but could not be reproducibly demonstrated. It occurred in 18- and 40-day-old cultures at a concentration of 3 × 10−3 μg GA3-equivalent/ml but was never seen in cultures of 12 days or less.