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Botulinum neurotoxin induces a potentially fatal paralytic condition in humans and various animal species collectively known as 'botulism'. It consequently poses a major problem to the food industry, due to the ability of its spores to survive in cooked foods. The incidence of wound botulism has also suffered a recent increase in the UK. The genome sequence of the C botulinum Group I strain ATCC 3502 has recently been determined. In silico analysis has revealed the presence of two distinct loci capable of encoding proteins with homology to AgrB and AgrD of the Staphylococcus aureus agr quorum sensing system. The functional characterisation of these genes has been carried out in order to determine whether they play a role in quorum sensing. To simplify laboratory procedures, C. sporogenes, the non-toxic counterpart of C. botulinum, was initially focused on. The agr regions in C. sporogenes were sequenced and their proteins compared with those of C. botulinum and other Gram-positive bacteria. Regions of conservation were observed amongst the clostridia and, to a lesser extent, between clostridia and staphylococci. Transcriptional linkage assays showed some of the genes of the C sporogenes agr regions to be co-expressed, and Real-Time RT-PCR demonstrated the maximal expression of these genes during late exponential growth. Modulation of the expression of the identified agr genes is a prerequisite to determining their function. Due to an initial lack of an effective gene knockout tool, antisense RNA expression was used for this purpose in C sporogenes, and showed that down regulation of the agrB genes affects sporulation. The development of an integrative vector system for gene inactivation in C sporogenes was also attempted. Knockout mutants in C botulinum and C sporogenes were later constructed using the newly-developed ClosTron system. These mutants were used to demonstrate that AgrDl, AgrD2 and an orphan sensor kinase protein all play a role in the control of sporulation in C. botulinum and C. sporogenes.