Factors Effecting on Indole-3-Acetic Acid Production by Resting Cells of Thermotolerant Acetic Acid Bacterium Asaia siamensis AB11-2

Acetic acid bacteria are a group of beneficial plants bacteria and some of them exhibit nitrogen

fixation activity and produce indole-3-acetic acid. Indole-3-acetic acid is an organic acid with hormonal

property that helps promote plants growth. A total of 6 isolates of nitrogen-fixing acetic acid bacteria

isolated from rice rhizoplane were examined for growth and indole-3-acetic acid production at high

temperatures. As the results, Asaia siamensis AB11-2 grew well at 37°C and produced indole-3-acetic

acid at 71 µg/ml. Factors effecting for indole-3-acetic acid production by thermotolerant A. siamensis

AB11-2 were observed at 37°C. The optimum conditions for indole-3-acetic acid production were resting

cells weight of 0.5 g, tryptophan 300 µg/ml, pH 5.0, aeration at 200 rpm gave the highest yield of indole-

3-acetic acid at 115 µg/ml when incubation at 36 hr. While production at 40°C could be as high as 98

µg/ml at 48 hr of incubation.