Streptomyces hygroscopicus subspecies hygroscopicus strain I18: Incubation time and tryptophan concentration effects on Indole-3-acetic acid (IAA) hormone production

Plant hormones are chemical messengers that regulate a wide range of physiological activities in plants. Microbes need a definite time to synthesize a compound. The microbial life cycle consists of several phases, often requiring a shorter incubation time than in complex organisms such as plants, animals, and humans. This study aimed to determine the optimum incubation time and the best tryptophan levels of Streptomyces hygroscopicus subsp. hygroscopicus strain i18 in.Indole-3-acetic acid (IAA) hormone. IAA has synthesized on liquid ISP4 medium using L-tryptophan supplementation as a precursor. Cell density was measured every day for 4-11 days using the spectrophotometric approach to track the incubation time. The doses of L-Tryptophan were 0, 1, 2, 3, 4, 5, and 6 mg/mL, respectively. The levels of IAA produced by bacteria were measured and compared with standard IAA. Streptomyces hygroscopicus subsp. hygroscopicus strain i18 was obtained the optimum incubation time at 9th days with an IAA level of 12.30 µg/mL. Supplementing with 5 mg/mL L-tryptophan resulted in the highest IAA level of 17.90 µg/mL. This study would be worthwhile in assisting agricultural product quality improvement through field application for further research.