A Novel Antidipteran Bacillus thuringiensis Strain: Unusual Cry Toxin Genes in a Highly Dynamic Plasmid Environment

Abstract

Bacillus thuringiensis has emerged as a major bioinsecticide on the global market. It offers a valuable alternative to chemical products classically utilized to control pest insects. Despite the efficiency of several strains and products available on the market, the scientific community is always on the lookout for novel toxins that can replace or supplement the existing products. In this study, H3, a novel B. thuringiensis strain showing mosquitocidal activity, was isolated from Lebanese soil and characterized in vivo at genomic and proteomic levels. H3 parasporal crystal is toxic on its own but displays an unusual killing profile with a higher 50% lethal concentration (LC50) than the reference B. thuringiensis serovar israelensis crystal proteins. In addition, H3 has a different toxicity order: it is more toxic to Aedes albopictus and Anopheles gambiae than to Culex pipiens. Whole-genome sequencing and crystal analysis revealed that H3 can produce 11 novel Cry proteins, 8 of which are assembled in genes with an orf1-gap-orf2 organization, where orf2 is a potential Cry4-type crystallization domain. Moreover, pH3-180, the toxin-carrying plasmid, holds a wide repertoire of mobile genetic elements that amount to ca. 22% of its size., including novel insertion sequences and class II transposable elements. Two other large plasmids present in H3 carry geneticdeterminants for the production of many interesting molecules—such as chitinase, cellulase, and bacitracin—that may add up to H3 bioactive properties. This paper therefore reports a novel mosquitocidal Bacillus thuringiensis strain with unusual Cry toxin genes in a rich mobile DNA environment © 2021 Fayad et al. This is an openaccess article distributed under the terms of the Creative Commons Attribution 4.0 International license.