Horizontal gene transfer of toxin genes in Clostridium botulinum

Abstract

Intoxication with the potent botulinum neurotoxin (BoNT) gives rise to the serious paralytic illness botulism. BoNT is part of a complex that consists of the neurotoxin and several associated components, all encoded by the bont gene cluster. This gene cluster has likely been subjected to horizontal gene transfer between different groups of clostridia, which has given rise to the genetically diverse species Clostridium botulinum. C. botulinum is divided into four physiological groups (I-IV), where group I and II cause disease in humans and group III in animals. Analysis of the genomes of group I, II and III has revealed that toxin genes, including the bont cluster, often are plasmid-borne. The genomes analyzed from group III contain an unusually high number of plasmids carrying different toxin genes. Some of these genes are also found in other Clostridium species and some have moved between different plasmids within the same physiological group. This indicates that horizontal transfer of toxin genes is taking place within and between species of Clostridium. The abundance of mobile elements, especially in genomes of group III, is likely connected to accelerated genome plasticity and gene transfer events.

Acknowledgments

This work was supported by/executed in the framework of the EU-project AniBioThreat (Grant Agreement: Home/2009/ISEC/AG/191) with the financial support from the Prevention of and Fight against Crime Programme of the European Union, European Commission—Directorate General Home Affairs. This publication reflects the views only of the author, and the European Commission cannot be held responsible for any use which may be made of the information contained therein.

Figures and Tables

Figure 1 Toxin genes in the BKT015925 plasmidome in comparison with gene location, i.e., on chromosome (chr), plasmid or phage, in the different groups of Clostridium botulinum and other Clostridium species. The title of each text box signifies the encoded toxin. The C2 toxin consists of two subunits, and is therefore encoded by two genes. *Located on different plasmids within C. botulinum group III.