Isolation and production of newly oligosporogenic polyvalent Bacillus thuringiensis mutants for agricultural pest control

To develop a new generation of eco-friendly biopesticides, this study used an optimized random mutagenesis approach to generates oligosporogenic mutants from B. thuringiensis var. kurstaki BLB1. Although random mutagenesis is not a novel approach, it remains a practical and efficient strategy providing a simple and accessible alternative. Screening of over than 600 mutants showed that only 14 clones harbour less rate of spores ranging from 1 ± 0.5 10 –6 to 126 ± 1 10 –6 spores ml −1 . Among them, a number of 6 mutants showed an improvement of delta-endotoxins until 222.92%. Protease production showed that S6 mutant exhibited the most increased rate of about 4136.36 U ml −1 ± 89.65 in addition to its enhancement of 34,96% in delta-endotoxins production. Captively, S3 and S4 mutants were largely active against A. tumefaciens and three fungi revealing values of MIC and MFC ranging from 0.07 to 0.31 µg ml −1 and from 0.05 to 0.225 µg ml −1 against A. niger , F. culmorum and B. cinerea , respectively. Oligosporogenic S6 mutant was considered as a polyvalent and eco-friendly biopesticide since it is the most toxic against semolina larvae E. kuehniella (LC 50 of 39.52 µg g −1 ). To reduce its production cost, we explored the use of date waste as a cost-effective culture medium. An improvement of 43.15% of delta-endotoxins production of S6 mutant was obtained via Taguchi design while valorising agricultural by-products. The study successfully generated oligosporogenic mutants of B. thuringiensis BLB1 with enhanced delta-endotoxin and enzyme production while reducing spore formation. The S6 mutant showed the highest bioactivity, and its production was further increased in a cost-effective way using date waste as a culture medium, highlighting its potential as a useful and eco-friendly biopesticide.