Role of Ger proteins in nutrient and nonnutrient triggering of spore germination in Bacillus subtilis

Dormant Bacillus subtilis spores germinate in the presence of particular nu trients called germinants. The spores are thought to recognize germinants t hrough receptor proteins encoded by the gerA family of operons, which inclu des gerA, gerB, and gerK. We sought to substantiate this putative function of the GerA family proteins by characterizing spore germination in a mutant strain that contained deletions at all known gerA-like loci. As expected, the mutant spores germinated very poorly in a variety of rich media. In con trast, they germinated like wild-type spores in a chemical germinant, a 1-1 chelate of Ca2+ and dipicolinic acid (DPA). These observations showed that proteins encoded by gerA family members are required for nutrient-induced germination but not for chemical-triggered germination, supporting the hypo thesis that the GerA family encodes receptors for nutrient germinants. Furt her characterization of Ca2+-DPA-induced germination showed that the effect of Cat(2+)-DPA on spore germination was saturated at 60 mM and had a K-m o f 30 mM. We also found that decoating spores abolished their ability to ger minate in Ca2+-DPA but not in nutrient germinants, indicating that Ca2+-DPA and nutrient germinants probably act through parallel arms of the germinat ion pathway.