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Germination at 37C of spores of Bacillus subtilis 1604 in the l-alanine and potassium phosphate (ALA) and the glucose, fructose, l-asparagine, potassium chloride (GFAK) germinant systems was triggered following heat activation at 70C for 1 h. In these conditions, 50% of the spore population became committed to germinate after exposure for 10 min and 14 min to ALA and GFAK, respectively, at which time 38% and 30% losses of OD600 had taken place. Dipicolinic acid (DPA) release, loss of heat resistance and release of soluble hexosamine-containing fragments occurred after commitment and were closely associated with loss of refractility in both the ALA and GFAK pathways. Net ATP synthesis could not be detected until 3–4 min after initiation of germination in both ALA and GFAK, by which time > 20% of the spore population was committed to germinate. The ALA and GFAK germination pathways were > 99% inhibited by 3 and 1 mm-HgCl2, respectively, as measured by OD600 loss. Reversible cost-commitment HgCl2-sensitive sites were present in the ALA and GFAK pathways which were 50% inhibited by 0·125 mm and 0·05 mm-HgCl2, respectively. A pre-commitment HgCl2-sensitive site was identified in the ALA pathway which was 55% inhibited by 6 mm-HgCl2. At 3 mm-HgCl2, 70% of the spore population became committed to germinate in the ALA pathway, whereas < 5% OD600 loss occurred. In this system, loss of heat resistance was associated with commitment, whereas OD600 loss and DPA release were identified as post-commitment events. The ALA and GFAK pathways were insensitive to a variety of metabolic inhibitors. Protease inhibitors had different effects on the ALA and GFAK pathways: phenylmethanesulphonyl fluoride (PMSF) solely inhibited ALA germination at a pre-commitment site and had little effect on GFAK germination, whereas N α-p-tosyl-l-arginine methyl ester (TAME) inhibited both the ALA and GFAK pathways at pre-and post-commitment sites. These results are discussed in relation to a recently proposed model for the triggering of Bacillus megaterium KM spore germination.