Enhanced sporulation and toxin production by a mutant derivative of Bacillus thuringiensis

Abstract

Bacillus thuringiensis (Bt) strains along with insecticidal crystal proteins (ICP) also produce proteases, and chitinases during growth and sporulation. These both potentate the activity of ICPs. This work aimed to obtain bioinsecticide over-production and thermotolerant mutant through classical mutagenesis of vegetative cells of Bt by using UV-mutation multiple times. The isolated survivors were screened on the basis of their production of β-glucosidase, delta-endotoxins and biomass in glucose-based medium. Maximum spore and crystal proteins were produced at 40°C with corn steep liquor as nitrogen source and hydrol as a carbon source. The best mutant MUV7 supported significantly (P = 0.0001) higher values of all kinetic parameters than those supported by the wild culture. Lower demand of activation energy (47.4 kJ mol^-1) for crystal protein formation revealed that the best mutant was comparable with those of thermophilic group of organisms.

Key words: Bioinsecticide, biomass, delta-endotoxin, insecticidal crystal proteins, kinetics, spores.