Bacterial endospores derive much of their longevity and resistance properties from the relative
dehydration of their protoplasts. The spore cortex, a
peptidoglycan structure surrounding the protoplasm, maintains, and is postulated to have a role in attaining, protoplast
dehydration. A structural modification unique to the spore cortex is the removal of all or part of the
peptide side chains from the majority of the
muramic acid residues and the conversion of 50% of the
muramic acid to
muramic lactam. A mutation in the cwlD gene of Bacillus subtilis, predicted to encode a muramoyl-
L-alanine amidase, results in the production of spores containing no
muramic lactam. These spores have normally dehydrated protoplasts but are unable to complete the germination/ outgrowth process to produce viable cells. Addition of germinants resulted in the triggering of germination with loss of spore refractility and the release of
dipicolinic acid but no degradation of cortex
peptidoglycan. Germination in the presence of
lysozyme allowed the cwlD spores to produce viable cells and showed that they have normal heat resistance properties. These results (i) suggest that a mechanical activity of the cortex
peptidoglycan is not required for the generation of protoplast
dehydration but rather that it simply serves as a static structure to maintain
dehydration, (ii) demonstrate that degradation of cortex
peptidoglycan is not required for spore solute release or partial spore core
rehydration during germination, (iii) indicate that
muramic lactam is a major specificity determinant of germination lytic
enzymes, and (iv) suggest the mechanism by which the spore cortex is degraded during germination while the germ cell wall is left intact.