Formulation for optimizing Bacillus thuringiensis production

Abstract

Bacillus thuringiensis Berliner, a gram positive aerobic bacterium, produces parasporal crystal (Cry) toxins that are highly specific and effective against insect species. During the course of isolation of native strains, B. thuringiensis AUG-5 was found the most effective with a wide range of activity against lepidopterans. Hence, different media were evaluated for its growth and development. Increase in concentration of the Luria Bertani [(LB), composed of casein, yeast extract and sodium chloride in 2:1:2 w/w)] medium in the fermentation broth from 1 to 2% increased colony forming unit (CFU), spore and also Cry1Ac and Cry2Ab toxin content. However, further increase of LB concentration to 3% adversely affected bacterial growth and development. Addition of 1% Wesson salt in 1% LB broth significantly increased spore, CFU counts, and also that of Cry1Ac but not of Cry2Ab. Spore and CFU counts in media were positively correlated and cell mass negatively correlated with Cry1Ac and Cry2Ab contents. Of all media substituting LB with agro products, medium consisting of 2% wheat flour, 2% soybean meal and 1% Wesson salt could be considered as an alternative to LB medium to achieve economy of largescale production costs. Spore-crystal complexes of Medium II and III were most toxic to the neonates of cotton bollworm, Helicoverpa armigera and tobacco caterpillar, Spodoptera litura at 10 µg/g, and differed significantly from those of Medium LB-2X and LB-3X and Cry2Ab2. Cry1Ac was most toxic to H. armigera at 1 µg/g and less toxic to S. litura than Cry2Ab.