Abstract
Improvement of the microbial strain by subjecting the genetic material to mutagenic agents offers an opportunity to reduce the production cost. This study aims to enhance the δ-endotoxin production of Bacillus thuringiensis strain S24 that is 2-fold more toxic than the commercialized strain HD1 against Ephestia kuehniella (Lepidoptera: Pyralidae) larvae through random mutagenesis. B. thuringiensis mutants were generated from the S24 strain by using nitrous acid, as chemical mutagenic agent. Three mutants (M29, M12 and M20) proved to be the most promising δ-endotoxin producer among 30 mutants analyzed in a screening program performed in shake flasks using a complex medium based on starch and soya bean. These mutants demonstrated an improvement of δ-endotoxin production of up to 21 and 74% compared with the parental wild strain S24 and HD1, respectively. The characterization of the over-producing mutants showed that their colony morphology, crystal shape, plasmid and protein patterns, cry gene content and toxicity are not affected by mutagenesis treatment. However, the crystal protein patterns of three under-producing mutants (M21, M14 and M11) were different to that of the parental wild strain. The high potentiality of the over-producing mutants makes them excellent candidates as biological agents for the control of pyralid stored-product pests.
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