Bacterial spore peptidoglycan (PG) is very loosely cross-linked relative to vegetative PG. Theories suggest that loosely cross-linked spore PG may have a flexibility which contributes to the attainment of spore core dehydration. The structure of the PG found in fully dormant spores has previously been examined in wild type and many mutant strains. These analyses showed little correlation between the degree of spore PG cross-linking and core dehydration. However, these studies only examined the structure of PG from dormant spores and did not allow for the structural analysis of spore PG during sporulation when actual spore PG synthesis and core dehydration occur.

Structural analyses of developing spore PG from wild type Bacillus subtilis and eight mutant strains are included in this study. Structural analyses of developing spore PG suggest the following: a) the germ cell wall PG is synthesized first next to the inner forespore membrane; b) cross-linking is relatively high in the first 10% of spore PG synthesized; b) a rapid decrease in cross-linking is observed during synthesis of the next 20% of the spore PG; and c) this decrease is followed by an eightfold rise in the degree of cross-linking during synthesis of the final 70% of the spore PG. This increasing gradient of cross-linking was previously predicted to contribute to the attainment of spore core dehydration. However, analyses of mutant strains indicate this cross-linking gradient is not required for the attainment of spore dehydration.