Unveiling the genomic landscape of NBAIR BtAe, a potential Bacillus thuringiensis strain against Holotrichia serrata F.

Abstract

Bacillus thuringiensis Berliner is a well-known biocontrol agent that produces insecticidal crystal proteins encoded by cry genes, which are effective against various insect orders. However, only a limited number of B. thuringiensis strains are known to be toxic to white grubs, a major pest of coconut, groundnut, and sugarcane that can cause up to 70%-80% yield losses. In this study, five indigenous B. thuringiensis strains, isolated from soil and Anomala elata cadavers, were screened for toxicity against second-instar Holotrichia serrata larvae, a highly destructive white grub species. Among them, the strain NBAIR BtAe exhibited the highest toxicity with an LC₅₀ of 115.36 μg mL-1. Whole-genome sequencing of NBAIR BtAe revealed a 5.67 Mb circular chromosome with 35.64% GC content. BtToxin_Digger analysis identified a novel cry gene with 39.57% similarity to cry21Aa2, along with other virulence genes including zwa6, zwa5A, chitinase C, inhA1, inhA2, bmp1, spp1Aa1, enhancin, and tpp80Ab1-like. These genes were validated through PCR. Additionally, genes encoding secondary metabolites such as lanthipeptides, paenilamicin, petrobactin, bacillibactin, and fengycin were detected. The presence of diverse pesticidal and antimicrobial genes highlights the potential of NBAIR BtAe as a promising candidate for bioinsecticide development targeting H. serrata in integrated pest management programs.