Indolyl-3-acetic acid formation byAzotobacter chroococcum

Summary Small amounts of indolyl-3-acetic acid (IAA) were detected in aerated cultures ofAzotobacter chroococcum grown with or withoutl-tryptophane in the medium, but IAA was detected in agar cultures only whenl-tryptophane was present. Most IAA was found in 7-day-old cultures and less in older cultures. Washed cells did not convert tryptophane enzymically to IAA. The time course of IAA formation byA. chroococcum strain A6 has been described and the effect of adding tryptophane to the medium has been studied. In contrast to results elsewhere strain A6 produced traces of IAA in aerated cultures with or without added tryptophane. IAA was detected only after the end of exponential growth when cells had begun to autolyse. The amount of IAA declined as cultures aged. The slight effect ofl- but not ofd-tryptophane in promoting IAA formation in ageing cultures suggests some kind of biological transformation but it seems unlikely that IAA formation is part of the normal metabolic processes of intact Azotobacter cells.