Sequence diversity of genes encoding botulinum neurotoxin type F

Area of Science:

• Microbiology
• Genetics
• Toxicology

Background:

• Botulism caused by type F botulinum neurotoxin (BoNT/F) is rare, accounting for less than 1% of cases.
• Limited isolation of BoNT/F-producing clostridial strains has hindered the analysis of bont/F gene diversity.

Purpose of the Study:

• To determine the nucleotide sequences of bont/F genes from various clostridial strains.
• To analyze the phylogenetic diversity of bont/F genes from environmental and outbreak-related isolates.

Main Methods:

• Sequencing of the entire bont/F nucleotide sequences from 33 type F botulinum toxin-producing clostridial strains.
• Phylogenetic analysis of proteolytic and nonproteolytic Clostridium botulinum type F strains, bivalent strains, and Clostridium baratii type F strains.

Main Results:

• Phylogenetic analysis identified seven distinct bont/F subtypes (F1-F7) with up to 25% nucleotide sequence divergence.
• Proteolytic C. botulinum strains yielded subtypes F1-F5, nonproteolytic strains yielded subtype F6, and C. baratii strains yielded subtype F7.
• The neurotoxin light chain region of bont/F5 was highly divergent, and the upstream ntnh/F gene showed variation within this subtype.

Conclusions:

• Extensive nucleotide diversity exists within bont/F genes from strains with different phylogenetic backgrounds and geographical origins.
• The study provides a comprehensive analysis of bont/F gene diversity, crucial for understanding the evolution and epidemiology of type F botulism.