Improvement of bioinsecticides production through mutagenesis of Bacillus thuringiensis by u.v. and nitrous acid affecting metabolic pathways and/or delta‐endotoxin synthesis

Aims:  The present work aimed to obtain bioinsecticide over‐producing mutants through classical mutagenesis of vegetative cells of Bacillus thuringiensis (Bt) by using u.v. and nitrous acid, and to evidence the involvement of cell metabolism in delta‐endotoxin synthesis. Methods and Results:  Vegetative cells of Bt were treated by nitrous acid (0·17 mg ml −1 ) or exposed to u.v. rays (emitted at a wave length of 240 nm). The isolated survivors were screened on the basis of the production of delta‐endotoxins and biomass in glucose and/or in gruel‐based media at two aeration conditions. Bioinsecticide over‐producing mutants were obtained with high frequencies because random mutations were shown to affect cell metabolism at different pathways related to the regulation of delta‐endotoxin synthesis. Conclusions:  Classical mutagenesis of Bt cells lead to the isolation of a large variety of delta‐endotoxin over‐producing mutants that could be classified into six groups based on the location of the mutations, particularly in metabolism pathways and delta‐endotoxin synthesis. Significance and Impact of the Study:  High frequencies of delta‐endotoxin over‐producing mutants of Bt could be obtained through classical mutagenesis of vegetative cells. This should contribute to a significant reduction of production and utilization costs of Bt bioinsecticides.