Bacillus toyonensis biovar Thuringiensis Bto_UNVM-42: A novel strain with potential for the biological control of nematodes

Bacillus toyonensis is a gram-positive bacterium within the Bacillus cereus group, primarily recognized for its probiotic properties. Recently, a strain designated B. toyonensis biovar Thuringiensis (Bto_UNVM-94) was reported to produce parasporal crystals with dual insecticidal activity against Cydia pomonella and Anthonomus grandis. In this study, we describe and characterize a previously undescribed strain, B. toyonensis biovar Thuringiensis Bto_UNVM-42, which exhibits nematicidal and nematostatic activity, representing the first report of these effects within this species. Whole-genome sequencing revealed the presence of a large plasmid containing multiple putative pesticidal genes, including five cry genes encoding Cry32-like proteins, two additional cry genes encoding Cry69-like and Cry73-like proteins, three cyt genes encoding Cyt1-like proteins, and two mpp genes encoding Mpp-like proteins. In addition, the genome encodes four chitinases and two proteins with significant similarity to the nematicidal Sep1 protease from Bacillus firmus. Proteomic analysis of parasporal crystals confirmed the expression of Cry32-family proteins. Bioassays showed that strain Bto_UNVM-42 was not toxic to Aedes aegypti, Alphitobius diaperinus, Anthonomus grandis, Cydia pomonella or Drosophila suzukii. In contrast, it exhibited nematicidal activity against Panagrellus redivivus, low but detectable mortality (8%) against Meloidogyne javanica, and a reversible nematostatic effect on Pratylenchus zeae. Taken together, the available bioassay observations and the genomic and proteomic data are consistent with a predominantly enzyme-driven rather than a classical crystal toxin-mediated mode of action. Overall, these findings expand the known biocidal spectrum of B. toyonensis and highlight its potential relevance for the development of biological strategies for nematode management.