Bacillus toyonensis biovar Thuringiensis: an overlooked entomopathogen?

Abstract

Horizontal gene transfer (HGT) significantly influences prokaryotic genome evolution. Bacillus cereus and Bacillus thuringiensis are nearly identical at the chromosomal level, except for B. thuringiensis producing parasporal crystals. The genes for these crystal proteins (e.g., cry1A), along with other encoded insecticidal proteins (e.g., vip3A), are located on megaplasmids and can be horizontally transferred. Recently, Sauka et al. (2022) reported a Bacillus toyonensis strain that produces parasporal crystals with dual insecticidal activity. This strain was classified as Bacillus toyonensis biovar Thuringiensis (NCBI: txid2923195) following Carroll et al.s (2020) nomenclature. Misclassified B. toyonensis strains, previously identified as B. thuringiensis (e.g., strain MC28), encode cry and cyt genes toxic to lepidopteran and dipteran insects. Advances in genome sequencing and bioinformatics tools now reduce misidentifications, enabling accurate reclassification in databases like GenBank. These findings highlight the need for genome-based taxonomic reassessment within the Bacillus cereus group and clarify the chromosomal placement of crystal-forming B. toyonensis strains.