Effects of cortex peptidoglycan structure and cortex hydrolysis on the kinetics of Ca(2+)-dipicolinic acid release during Bacillus subtilis spore germination

The kinetic parameters of the release of Ca(2+)-dipicolinic acid (CaDPA) during germination of spore populations and multiple individual spores of Bacillus subtilis strains with major alterations in the structure of the spore peptidoglycan (PG) cortex or lacking one or both of the two redundant enzymes involved in cortex hydrolysis (cortex-lytic enzymes CLEs]) were determined. The lack of the CLE CwlJ greatly slowed CaDPA release with a germinant receptor (GR)-dependent germinant, l-valine, or a non-GR-dependent germinant, dodecylamine. The absence of the cortex-specific PG modification muramic acid-δ-lactam also increased the time needed for full CaDPA release during germination with both types of germinants. In contrast, increased cortex PG cross-linking was associated with faster times for initiation of CaDPA release with both l-valine and dodecylamine but not with faster CaDPA release once this release had been initiated. These data suggest that the precise structure of the spore cortex plays a significant role in determining the timing and the rate of CaDPA release during B. subtilis spore germination and, further, that this effect is independent of effects of GRs.