BoNTax: a curated genome-based framework for taxonomic classification and characterization of Clostridium botulinum Group I and Clostridium sporogenes

Abstract

Clostridium botulinum Group I and Clostridium sporogenes are closely related genomic lineages for which historical toxin-based nomenclature can obscure species-level relationships. We developed BoNTax, a curated taxonomy-first framework that separates average nucleotide identity (ANI)-based species assignment from botulinum neurotoxin (BoNT) characterization while integrating assembly quality assessment, multilocus sequence typing (MLST), AMRFinderPlus-based detection of bont genes, other virulence-associated genes, and antimicrobial resistance genes into standardized outputs. Analysis of 966 genomes informed genome-size criteria and the selection of 46 representative references comprising 22 C. botulinum Group I and 24 C. sporogenes genomes. Pairwise ANI resolved these references into two distinct species clusters: within-species ANI values were >95%, whereas between-species values were <95%, supporting a 95% species-level assignment threshold. BoNTax was implemented in GalaxyTrakr as complementary FASTQ- and FASTA-input workflows that converge on a common downstream analysis. The workflow completed analysis of all 42 validation genomes. Among the 32 genomes with a reported taxonomic identity, 29 assignments were concordant and three prompted taxonomic re-evaluations. For the ten genomes reported as taxonomically unknown, BoNTax provided ANI-based assignments. Of the three discordances, BT-22100019 was assigned to C. sporogenes rather than the reported C. botulinum Group I, whereas R1125/03 and R1135/03 showed 99.96% ANI to C. caseinilyticum DSM 46279, supporting their identification as C. caseinilyticum. MLST assignments were concordant for genomes with established profiles except PNUSAB000061, for which ST183 was not assigned by the MLST database version used in this analysis. BoNT type and subtype detection was fully concordant across toxigenic genomes, including bivalent strains. Thirty-one genomes met the predefined assembly-size QC criterion, whereas 11 received QC warnings, including all eight datasets representing four known mixed cultures. BoNTax therefore provides a reproducible genomic framework for resolving closely related clostridial lineages, identifying taxonomic annotations requiring re-evaluation, and reporting clinically relevant toxin information without conflating toxin genotype with species identity.