Abstract
Clostridium botulinum is a dangerous pathogen that forms the highly potent botulinum toxin, which when ingested causes a deadly neuroparalytic disease. The closely related Clostridium sporogenes is occasionally pathogenic, frequently associated with food spoilage and regarded as the non-toxigenic equivalent of Group I C. botulinum. Both species form highly resistant spores that are ubiquitous in the environment and which, under favourable growth conditions germinate to produce vegetative cells. To improve the control of botulinum neurotoxin-forming clostridia, it is imperative to comprehend the mechanisms by which spores germinate. Germination is initiated following the recognition of small molecules (germinants) by a specific germinant receptor (GR) located in the spore inner membrane. The present study precisely defines clostridial GRs, germinants and co-germinants. Group I C. botulinum ATCC3502 contains two tricistronic and one pentacistronic GR operons, while C. sporogenes ATCC15579 has three tricistronic and one tetracistronic GR operons. Insertional knockout mutants, allied with characterisation of recombinant GRs shows for the first time that amino acid stimulated germination in C. botulinum requires two tri-cistronic encoded GRs which act in synergy and cannot function individually. Spore germination in C. sporogenes requires one tri-cistronic GR. Two other GRs form part of a complex involved in controlling the rate of amino-acid stimulated germination. The suitability of using C. sporogenes as a substitute for C. botulinum in germination studies and food challenge tests is discussed.
Highlights
Clostridium botulinum and Clostridium sporogenes are closely related anaerobic spore-forming bacteria
Germination is initiated following the recognition of small molecules by a specific germinant receptor (GR) located within spores
The present study has characterised two functionally active GRs in C. botulinum which act in synergy and cannot function individually, and a related functionally active GR in C. sporogenes
Summary
Clostridium botulinum and Clostridium sporogenes are closely related anaerobic spore-forming bacteria. C. botulinum is a dangerous pathogen that forms the deadly botulinum neurotoxin. This is the most potent toxin known, as little as 30–100 ng can be fatal [1]. The botulinum neurotoxins are 150 kD proteins with zinc-endopeptidase activity that block acetylcholine transmission in cholinergic nerves, leading to a floppy paralysis known as botulism, that may prove fatal to both humans and animals [6,7]. Foodborne botulism is an intoxication caused by consumption of neurotoxin formed by C. botulinum following spore germination and growth of vegetative cells in food. Infant and wound botulism are infections involving spore germination, growth of vegetative cells and neurotoxin formation in the gut of young infants and in deep wounds (often associated with drug abuse), respectively. Botulinum neurotoxins are important pharmaceuticals used to treat a range of localised conditions e.g. blepharospasm, hemifacial spasm, and for cosmetic purposes [9]
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