Molecular and Physiological Characterisation of Spore Germination in Clostridium botulinum and C. sporogenes

Germination is the first step in the development of dormant spores into exponentially dividing cells. Spore germination in proteolytic Clostridium botulinum type B and in C. sporogenes was triggered strongly byL -alanine/L -lactate/NaHCO₃, less well by L-alanine/NaHCO₃, but not by inosine or the AGFK mixture (asparagine, glucose, fructose and potassium ions). This suggests the presence of a functional equivalent of the L-alanine receptor encoded by the gerA operon in Bacillus subtilis, while germination genes that respond to inosine (gerI in Bacillus cereus) and AGFK mixture (gerB/gerK in B. subtilis) appear to be absent. Putative gerA operons of proteolytic C. botulinum type B and C. sporogenes have been identified using PCR with degenerate primers and show a similar genetic arrangement with the gerAA and gerAB genes, encoding the GerAA and GerAB proteins. In both species, a third partial ORF may encode a GerAC homologue. The GerAA and GerAB proteins have homology with GerAA and GerAB proteins from other Clostridium and Bacillus species with the highest homology between the C. botulinum and C. sporogenes proteins. The GerAA proteins of these species have six putative transmembrane α -helices similar to other L -alanine-dependent germination GerAA proteins suggesting a membrane location. Expression studies in C. botulinum showed that the gerAA and gerAB genes are co-transcribed during sporulation.