Phytohormone, indole-3-acetic acid (IAA), is an important compound involved in plant growth and stress response. Endophytes promote plant growth through IAA by induction of root proliferation and cell elongation. Micrococcus luteus 4.43, an endophytic bacterium, produced IAA with tryptophan as a precursor. The optimum condition of IAA biosynthesis was a culture medium supplemented with 5 mg/ml of L-tryptophan at pH 7, incubated at 30°C for 72 h, and inoculated with cell number at 106 CFU/ml. The inoculum size, tryptophan concentration, and incubation time exhibited a positive correlation with IAA production; pH and temperature showed a negative correlation. The supernatant of cell culture obtained IAA and crude extract of IAA was stable to heat (121°C, 15 min) and light exposure (1000 lux) for 30 days; the IAA sample was stored effectively in dark at 4°C for up to 2 months. The intermediate compounds of IAA synthesis were detected using HPLC to demonstrate the IAA biosynthesis pathway of M. luteus 4.43 via an indole-3-acetonitrile pathway.
Key words: Indole-3- acetamide, Indole-3-acetonitrile, Endophytic bacteria, Micrococcus luteus
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