Multiple cry Genes in Bacillus thuringiensis Strain BTG Suggest a Broad-Spectrum Insecticidal Activity

Abstract

The properties of Bacillus thuringiensis strains as a biopesticide with potent action against moths, beetles, and mosquitoes have been known for decades, with individual subspecies showing specific activity against a particular pest. The aim of the present work is to characterize strains that can be used for broad-spectrum pest control in agriculture. Twenty strains of B. thuringiensis were isolated from Bulgarian soil habitats. The strains were screened for genes encoding 12 different crystal (Cry) endotoxins by PCR with specific primer pairs. Seven of the isolates contained cry genes in their genomes. B. thuringiensis strains PL1, PL3, and PL20 contained at least three different cry genes, while B. thuringiensis serovar galleriae BTG contained at least four. Moreover, scanning electron microscopy (SEM) investigation revealed the production of bipyramidal (PL1, PL3, PL20), polygonal (PL1), cubic (BTG), and spherical crystals (BTG and PL20). Potentially containing the most cry genes, the BTG genome was sequenced and annotated. It comprises 6,275,416 base pairs, does not contain plasmids, has a GC content of 35.05%, and contained 7 genes encoding crystal toxins: cry1Ab35, cry1Db, cry1Fb, cry1Ib, cry2Ab, cry8Ea1, and cry9Ba. This unique combination would possibly enable the simultaneous pesticidal action against pest species from orders Lepidoptera, Coleoptera, Diptera, and Hemiptera, as well as class Gastropoda. Whole-genome sequencing provided accurate information about the presence, localization, and classification of Cry toxins in B. thuringiensis BTG, revealing the great potential of the strain for the development of new broad-spectrum bio-insecticides.