Abstract: Seven IAA(indole-3-acetic)-producing strains were isolated from the rhizosphere of peanuts growing in red soil. Among the 7 strains, Strain L4 was the highest in IAA excreting capability (135.67 μg•mL^-1 in 24 h of cultivation), in addition to its phosphate-dissolving capability. Based on its morphological feature, some of its physiological and biochemical characteristics and its 16S rRNA sequence analysis, it was identified as Arthrobacter chlorophenolicus (GenBank Accession No. JQ277449). Single factor tests were designed to explore conditions optimal to growth and fermentation of the strain. Results show that the optimum conditions for its growth differed from those for its IAA excretion. The conditions optimal both to its growth and to its IAA secretion as well were 5-6 in initial pH, volume 50 mL•250 mL^-1 in liquid volume in flask, 30 ℃ in temperature, and 24 h of shaking culture. The best carbon and nitrogen sources for its growth was maltose and yeast extract, but for its IAA production, xylose and KNO₃, respectively.

Key words: red soil, PGPR, indole-3-acetic acid (IAA), optimization