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

Brian H Raphael,Suzanne R Kalb,John R Barr,Laura I T De Jong,Carolina Lúquez,Michael Frace,Rafael A Fernández,Matthew Lautenschlager,Susan E Maslanka

doi:10.1186/1471-2180-12-245

Brian H Raphael, Suzanne R Kalb + Show 7 more

Open Access

https://doi.org/10.1186/1471-2180-12-245

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Abstract

BackgroundClostridium 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.ResultsGenetic 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).ConclusionsThese 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.

Highlights

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
Clostridium botulinum type E strains can be isolated from various marine environments and cases of botulism due to botulinum neurotoxins (BoNT)/E typically occur in Canada, Alaska, Northern Europe, and Japan [3]
A recent outbreak of botulism in birds and fish in the Great Lakes region was attributed to genetically distinct strains of C. botulinum type E and the organism was found in lake sediment [6]

Summary

Introduction

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. Strains of Clostridium botulinum producing BoNT/E share similar metabolic characteristics including the inability to digest proteins such as gelatin, casein, or meat. These nonproteolytic strains are psychrophilic with the ability to grow at refrigeration temperatures [1]. Clostridium botulinum type E strains can be isolated from various marine environments and cases of botulism due to BoNT/E typically occur in Canada, Alaska, Northern Europe, and Japan [3]. A case of infant botulism occurred in Illinois in 2007 the source of spores in this case could not be determined [7]

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