A recently published IFR paper in PLOS Pathogens describes evidence for two functionally active germination receptors in Clostridium botulinum which act in synergy and cannot function individually, and a related functionally active germination receptor in Clostridium sporogenes.
Here, Dr Jason Brunt, an IFR scientist working in Professor Mike Peck’s research group within the GHFS Research Programme, blogs about the research behind this new paper.
The major hazards presented by Clostridium botulinum and its associated neurotoxinshave been vividly illustrated by two recent events, both of which received substantial coverage in the scientific and non-scientific literature. Firstly, a pair of articles published by scientists from California in the J. Infectious Disease describing a new botulinum neurotoxin (called type H) formed by a strain of C. botulinum isolated following a case of infant botulism. Such was the concern (from a bioterrorism perspective) that it was decided not to publish full details of this new botulinum neurotoxin until appropriate countermeasures were in place. Secondly, the consequences of the apparent detection of C. botulinum in powdered milk in New Zealand have been dramatic, with the recall of over 38 tonnes of whey protein and an associated massive economic cost amounting to hundreds of millions of dollars. This led to some loss of confidence in this product which is sold across the globe, and is a significant fraction of the GDP of New Zealand. The economic impact would have been far worse if even a single case of human botulism had resulted. In fact, the most recent information indicates that the organism isolated from the milk was the closely-related C. sporogenes rather than C. botulinum.
Although published research has traditionally focussed on the genetics and production of the neurotoxins, in practice much of the hazard posed to human health is due to the fact that this organism forms very heat-resistant spores which persist in the environment and so are often present in raw food ingredients. To improve the control of botulinum neurotoxin-forming clostridia, it is imperative to comprehend the mechanisms by which these spores germinate. Currently, our knowledge of the mechanisms by which Gram positive bacterial spores germinate relies almost entirely on studies of the aerobe Bacillus, an organism with different genetics and biochemistry. Our paper published in PLoS Pathogens is the first to address such a large gap in scientific knowledge by focussing specifically on the germination mechanisms of C. botulinum and the closely related C. sporogenes. We have used a combination of gene insertional knockouts, complementation and phenotypic germination studies to determine which of the several germinant receptor operons present in the Group I C. botulinum chromosome are functionally important. This approach, refined by a detailed analysis of the effects of different combinations of germinant molecules has enabled us to define C. botulinum germination. In particular, we showed for the first time that amino acid stimulated germination in C. botulinum requires two tri-cistronic encoded germinant receptors (GRs) which act in synergy and cannot function individually. Spore germination in C. sporogenes requires one tri-cistronic GR, with two other GRs forming part of a complex involved in controlling the rate of amino-acid stimulated germination.The long term aim is that as more is understood of the complex germination systems in clostridia, it may be conceivable to formulate detailed strategies to interrupt this process. This would be of great benefit to help control pathogenic clostridia, for the food industry.