Diversity of the Germination Apparatus in Groups I, II, III, and IV.

is a highly dangerous pathogen that forms very resistant endospores that are ubiquitous in the environment, and which, under favorable conditions germinate to produce vegetative cells that multiply and form the exceptionally potent botulinum neurotoxin. To improve the control of botulinum neurotoxin-forming clostridia, it is important to understand the mechanisms involved in spore germination. Here we present models for spore germination in based on comparative genomics analyses, with Groups I and III sharing similar pathways, which differ from those proposed for Groups II and IV. All spores germinate in response to amino acids interacting with a germinant receptor, with four types of germinant receptor identified [encoded by various combinations of , and genes ()]. There are three gene clusters with an ABC-like configuration; ABC [], ABABCB [] and ACxBBB [], and a single CA-B [] gene cluster. Subtypes have been identified for most germinant receptor types, and the individual GerX subunits of each cluster show similar grouping in phylogenetic trees. Group I contained the largest variety of subtypes, with three , three , and one subtypes, while Group III contained two types and one . Groups II and IV contained a single germinant receptor, and , respectively. It is likely that all four Groups include a SpoVA channel involved in dipicolinic acid release. The cortex-lytic enzymes present in Groups I and III appear to be CwlJ and SleB, while in Groups II and IV, SleC appears to be important.