Characterization of auxin production plant growth promotion by a bacterium isolated from button mushroom compost

An auxin-producing bacterial strain, designated 4-3, was isolated from waste button mushroom compost in Boryeong-si, Chungnam. The strain 4-3 was classified as a novel strain of Leucobacter tardus, based on chemotaxonomic and phylogenetic analyses. TLC and HPLC the isolated L. tardus strain 4-3 produced indole-3-acetic acid (IAA), the auxin. Maximum IAA productionof 94.3 mg L-1 was detected for bacteria cultured in R2A medium with 0.1% l-tryptophan, incubated for 24 h at 35oC. Negative correlationwas observed between IAA production and pH of the culture medium, indicating that the increase inIAA caused acidification ofthe medium. The effect of supplementation with varying concentrations of l-tryptophan, a known precursor of IAA, was also assessed. production was maximal at 0.1% l, but decreased at lconcentrations above 0.2%. To investigate the plant growth-promoting effects of the bacterium, L. tardus strain 4-3 culture broth was used to inoculate water cultures and seed pots of mung bean. We found thatadventitious root induction and root growth were 2.2-times higher in thethan in the non-inoculated plants.