Genetic requirements for induction of germination of spores of Bacillus subtilis by Ca2+-dipicolinate

Dormant Bacillus subtilis spores can be induced to germinate by nutrients, as well as by nonmetabolizable chemicals, such as a 1:1 chelate of Ca2+ and dipicolinic acid (DPA). Nutrients bind receptors in the spore, and this bi nding triggers events in the spore core, including DPA excretion and rehydr ation, and also activates hydrolysis of the surrounding cortex through mech anisms that are largely unknown. As Ca2+-DPA does not require receptors to induce spore germination, we asked if this process utilizes other proteins, such as the putative cortex-lytic enzymes SleB and CwlJ, that are involved in nutrient-induced germination. We found that Ca2+-DPA triggers germinati on by first activating CwlJ-dependent cortex hydrolysis; this mechanism is different from nutrient-induced germination where cortex hydrolysis is not required for the early germination events in the spore core. Nevertheless, since nutrients can induce release of the spore's DPA before cortex hydroly sis, we examined if the DPA excreted from the core acts as a signal to acti vate CwlJ in the cortex. Indeed, endogenous DPA is required for nutrient-in duced CwlJ activation and this requirement was partially remedied by exogen ous Ca2+-DPA. Our findings thus define a mechanism for Ca2+-DPA-induced ger mination and also provide the first definitive evidence for a signaling pat hway that activates cortex hydrolysis in response to nutrients.