Botulinum Neurotoxin-Producing Bacteria. Isn't It Time that We Called a Species a Species?

Abstract

Botulinum neurotoxins (BoNTs) are produced by a diverse set of seven clostridial species, though alternate naming systems have developed over the last 100 years. Starting in the 1950s, a single-species taxonomy where any bacterium producing BoNT would be designated Clostridium botulinum was introduced. As the extreme diversity of these strains was recognized, a secondary system of taxonomic "groups" evolved. It became clear that these groups also had members that did not produce BoNT, and in some cases, they were given formal species names. Genomic analysis now clearly identifies species affiliations whether an isolate is toxigenic or not. It is clear that C. botulinum group nomenclature is no longer appropriate and that there are recognized species names for each clostridium. We advocate for the use of the scientific binomials and that the single-species group nomenclature be abandoned.

Keywords: Clostridium botulinum; botulinum neurotoxin; botulism; phylogenetic analysis; taxonomy.

FIG 1

Dendrograms of BoNT-producing bacteria and closely related isolates. DNA sequence analysis of 54 isolates using 16S rRNA gene sequences (aligned with MUSCLE [32]) and maximum-likelihood analysis (IQ-TREE [33, 34]) (A) and using whole-genome sequences to estimate average nucleotide identity (ANI) with Mash (k = 21, s = 1,000,000) (30) followed by clustering with the unweighted pair group method with arithmetic mean (UPGMA) within QIIME (35) (B). Both methods separate the isolates into 7 taxonomic categories consistent with the historical species designations.