Dipicolinic Acid Release by Germinating Spores Occurs Through a Mechanosensing Mechanism

Classically, dormant endospores are defined by their resistance properties, particularly their resistance to heat. Much of the heat resistance is due to the large amount of dipicolinic acid (DPA) stored within the spore core. During spore germination, DPA is released and allows for rehydration of the otherwise-dehydrated core. In , 7 proteins are encoded by the operon and are important for DPA release. These proteins receive a signal from the activated germinant receptor and release DPA. This DPA activates the cortex lytic enzyme CwlJ, and cortex degradation begins. In , spore germination is initiated in response to certain bile acids and amino acids. These bile acids interact with the CspC germinant receptor, which then transfers the signal to the CspB protease. Activated CspB cleaves the cortex lytic enzyme, pro-SleC, to its active form. Subsequently, DPA is released from the core. encodes orthologues of , , and . Of these, the SpoVAC protein was shown to be capable of mechanosensing. Because cortex degradation precedes DPA release during spore germination (opposite of what occurs in ), we hypothesized that cortex degradation would relieve the osmotic constraints placed on the inner spore membrane and permit DPA release. Here, we assayed germination in the presence of osmolytes, and we found that they can delay DPA release from germinating spores while still permitting cortex degradation. Together, our results suggest that DPA release during spore germination occurs though a mechanosensing mechanism. is transmitted between hosts in the form of a dormant spore, and germination by spores is required to initiate infection, because the toxins that are necessary for disease are not deposited on the spore form. Importantly, the spore germination pathway represents a novel pathway for bacterial spore germination. Prior work has shown that the order of events during spore germination (cortex degradation and DPA release) is flipped compared to the events during spore germination, a model organism. Here, we further characterize the spore germination pathway and summarize our findings indicating that DPA release by germinating spores occurs through a mechanosensing mechanism in response to the degradation of the spore cortex.