Novel Putative Transposable Element Associated with the Subtype E5 Botulinum Toxin Gene Cluster of Neurotoxigenic Clostridium butyricum Type E Strains from China

Abstract

Previously, a whole-genome comparison of three Clostridium butyricum type E strains from Italy and the United States with different C. botulinum type E strains indicated that the bont/e gene might be transferred between the two clostridia species through transposition. However, transposable elements (TEs) have never been identified close to the bont/e gene. Herein, we report the whole genome sequences for four neurotoxigenic C. butyricum type E strains that originated in China. An analysis of the obtained genome sequences revealed the presence of a novel putative TE upstream of the bont/e gene in the genome of all four strains. Two strains of environmental origin possessed an additional copy of the putative TE in their megaplasmid. Similar putative TEs were found in the megaplasmids and, less frequently, in the chromosomes of several C. butyricum strains, of which two were neurotoxigenic C. butyricum type E strains, and in the chromosome of a single C. botulinum type E strain. We speculate that the putative TE might potentially transpose the bont/e gene at the intracellular and inter-cellular levels. However, the occasional TE occurrence in the clostridia genomes might reflect rare transposition events.

Advances in Clostridial and Related Neurotoxins

“…Since we have not yet resolved the evolutionary forces driving BoNT uptake, maintenance, and diversity in clostridia and related organisms, we may under-appreciate the diversity and functional distinctions of the many members of the BoNT family of protein toxins concerning human pathology and pharmacology. One study in this Special Issue that addresses the horizontal transfer of bont genes in clostridia describes the identification of transposable elements associated with BoNT/E5 in C. butyricum [19]. Previous studies have indicated the potential horizontal transfer of bont genes by plasmid conjugation combined with potential chromosomal plasmid integration events and proposed the descent of bont genes from a precursor protein family with adaptation towards developing into toxins producing vertebrate paralysis followed by diversification [1,20,21].…”