TAF PUBLISHING

Plant Growth Promoting Bacteria (PGPB) have been considered as beneficial microorganisms that can promote plant growth by their potential mechanism, particularly Indole-3-Acetic Acid (IAA) production. Lysinibacillus fusiformis UD 270 isolated from local plants in Khon Kaen, Thailand displayed its capability to produce IAA from tryptophan well-known as its precursor. Thus, the study was investigated in IAA biosynthesis with different concentrations of tryptophan and bacterial cell number as well as observed the correlation between bacterial growth and IAA production. The bacteria were grown in nutrient broth supplemented with 0, 0.5, 1, 2, 3, 4, and 5 mg mL-1 of tryptophan at 30oC for 72h. Reasonable bacterial growth and IAA production were appreciably determined at 36h of incubation in 5 mg mL-1 of tryptophan. Meanwhile, the pH of the culture media was gradually increased at the beginning and made stable after 36h. Moreover, when the cell concentration was varied from 103 to 109 Colony-Forming Unit (CFU) mL-1, the IAA production was significantly higher at high cell concentrations, concretely with 107 and 109 CFU mL-1. Also, a positive correlation between growth and IAA production was indicated in the two experiments. The results have referred for the suitable uses of tryptophan and cell number for bacterial growth and IAA biosynthesis of L. fusiformis UD 270 to apply for further researches.