Culture growth and IAA production by a microbial diazotropic symbiont of stem-nodules of the legumeAeschynomene aspera

The stem nodules of the legumeAeschynomene aspera contain indoleacetic acid and a high amount of tryptophan. TheAzorhizobium caulinodans isolated from the stem nodules of the leguminous emergent hydrophyte produced a high amount of IAA (14.8 mg/L) inl-tryptophan-supplemented basal medium. The IAA yields paralleled the culture growth rate and increased up to 52 h. No separate growth and production phase was observed. The IAA production was increased 344% when the medium was supplemented withl-tryptophan, sucrose, FeSO₄·7H₂O, NaNO₃, ascorbic acid and sodium dodecyl sulfate. The possible role of the IAA production in the legume-bacterium symbiosis is discussed.