Species identity does not predict pesticidal gene content in the Bacillus thuringiensis group: comparative genomics of strains originally recognized as B. thuringiensis against reference genomes
Year: 2026
Type: preprint
Abstract: Background Bacillus thuringiensis is distinguished from Bacillus cereus by a plasmid-encoded phenotype, the synthesis of insecticidal and cytocidal proteins, known as Cry and Cyt, respectively, whereas genome-based classification uses chromosomal genes. We asked whether species identity predicts the presence of pesticidal genes in the B. cereus group. Results Three soil strains producing a parasporal inclusion originally identified as B . thuringiensis were compared with seventeen reference genomes. Average nucleotide identity (ANI), digital DNA–DNA hybridization (dDDH) and a core-genome phylogeny resolved all three assignments concordantly: GM18 was B. toyonensis (98.87% ANI, 90.5% dDDH, sister to BCT-7112T at 100% bootstrap), IB84 B. albus (97.82%; 80.2%), and L4J2 fell in a near-clonal clade with two subsp. israelensis references (99.97% ANI). Gene content differed. L4J2, deposited as B. cereus group, carried the complete canonical mosquitocidal cassette — Cry4, Cry10, Cry11, Cyt1 and Cyt2 — at named-gene identity and entirely on plasmids; GM18 carried no cry or cyt gene, sharing almost no toxin content with its own type strain; IB84 carried no classical insecticidal locus, nor did two reference strains deposited as B. thuringiensis . Below the species boundary, the toxin families shared by two genomes were unrelated to how closely related they were. Toxin loci were enriched 4.54-fold on plasmids and lay closer to insertion sequences than expected, whereas virulence factors were not. Seven of ten reference strains deposited as B. thuringiensis , including the kurstaki strains used commercially, are assigned to B. cereus genomically. Conclusions Published bioassays of the three strains agree with these predictions, although no claim of insecticidal activity is made here. Species identification cannot substitute for direct gene-content profiling in biocontrol prospecting.
Source: Research Square
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7225782726