Open Access Highly Accessed Research article

Analysis of a unique Clostridium botulinum strain from the Southern hemisphere producing a novel type E botulinum neurotoxin subtype

Brian H Raphael1*, Matthew Lautenschlager1, Suzanne R Kalb1, Laura I T de Jong2, Michael Frace1, Carolina Lúquez1, John R Barr1, Rafael A Fernández2 and Susan E Maslanka1

Author affiliations

1 Centers for Disease Control and Prevention, 1600 Clifton Road, MS G-29, Atlanta, GA, 30329, USA

2 Area Microbiología, Universidad Nacional de Cuyo, Mendoza, Argentina

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Citation and License

BMC Microbiology 2012, 12:245  doi:10.1186/1471-2180-12-245

Published: 31 October 2012

Abstract

Background

Clostridium botulinum strains that produce botulinum neurotoxin type E (BoNT/E) are most commonly isolated from botulism cases, marine environments, and animals in regions of high latitude in the Northern hemisphere. A strain of C. botulinum type E (CDC66177) was isolated from soil in Chubut, Argentina. Previous studies showed that the amino acid sequences of BoNT/E produced by various strains differ by < 6% and that the type E neurotoxin gene cluster inserts into the rarA operon.

Results

Genetic and mass spectral analysis demonstrated that the BoNT/E produced by CDC66177 is a novel toxin subtype (E9). Toxin gene sequencing indicated that BoNT/E9 differed by nearly 11% at the amino acid level compared to BoNT/E1. Mass spectrometric analysis of BoNT/E9 revealed that its endopeptidase substrate cleavage site was identical to other BoNT/E subtypes. Further analysis of this strain demonstrated that its 16S rRNA sequence clustered with other Group II C. botulinum (producing BoNT types B, E, and F) strains. Genomic DNA isolated from strain CDC66177 hybridized with fewer probes using a Group II C. botulinum subtyping microarray compared to other type E strains examined. Whole genome shotgun sequencing of strain CDC66177 revealed that while the toxin gene cluster inserted into the rarA operon similar to other type E strains, its overall genome content shared greater similarity with a Group II C. botulinum type B strain (17B).

Conclusions

These results expand our understanding of the global distribution of C. botulinum type E strains and suggest that the type E toxin gene cluster may be able to insert into C. botulinum strains with a more diverse genetic background than previously recognized.

Keywords:
Botulism; Mass spectrometry; Genomics; Whole genome sequencing