Indole -3-Acetic Acid Production by the Bacterial Strains Isolated from Vermicomposts in the Presence and Absence of Tryptophan

ABSTRACT: Vermicompost was prepared from leaf materials such as Gliricidia sepium Jacq, Leucaena leucocephala (Lam.) De Wit and Cassia auriculata Linn and earthworms, Eudrilus eugeniae (Kinberg) and Eisenia fetida (Savigny) along with cowdung in six Treatments. Fortnightly analyses (0, 15, 30, 45 and 60 d) of the colony forming units (CFU) of bacteria in vermicomposts, vermicasts and earthworm guts (fore, mid and hind) showed that vermicompost prepared using C.auriculata + L.leucocephala + Cowdung mixture with E.eugeniae is the best of all six treatments. Nine bacterial strains which have the capability to produce Indole-3-acetic acid (IAA) were screened they were Streptococcus spp. (18.78 μg/ml), Micrococcus spp. (5.99 μg/ml), Klebsiella spp. (5.69 μg/ml), Bacillus spp. (18.99 μg/ml), Enterobacter spp. 6.10 μg/ml), Escherichia spp. 6.38 μg/ml), Alcaligenes spp. (10.75 μg/ml), Erwinia spp. (15.77 μg/ml), and Pseudomonas spp. (18.67 μg/ml). The quantities of IAA produced by all these nine bacterial strains were estimated using spectrophotometer. Among all the nine bacterial strains tested one strain (i.e) Bacillus spp. Showed significantly higher quantity of IAA production. Hence the bacterial strain was taken for further molecular analysis and identified as Bacillus cereus. Attempt has also been made to standardize the production of IAA by B.cereus in different tryptophan concentrations (1, 2, 3, 4 and 5mg/ml), at different pH (5, 7 and 9), at different temperatures (28 37 and 45 C) and at different day (1 to 7 day) intervals. The results showed that the tryptophan concentration at which IAA production was higher was in the order of 5>4>3>2>1 mg/ml at pH 7 followed by 5 and 9. The suitable temperature was 37C followed by 28 and 45C. The number of days required for higher rate of production of IAA was in the order of 7>6>5>4>2>1 compared to others.