Contributions of Four Cortex Lytic Enzymes to Germination of Bacillus anthracis Spores

Abstract

ABSTRACT Bacterial spores remain dormant and highly resistant to environmental stress until they germinate. Completion of germination requires the degradation of spore cortex peptidoglycan by germination-specific lytic enzymes (GSLEs). Bacillus anthracis has four GSLEs: CwlJ1, CwlJ2, SleB, and SleL. In this study, the cooperative action of all four GSLEs in vivo was investigated by combining in-frame deletion mutations to generate all possible double, triple, and quadruple GSLE mutant strains. Analyses of mutant strains during spore germination and outgrowth combined observations of optical density loss, colony-producing ability, and quantitative identification of spore cortex fragments. The lytic transglycosylase SleB alone can facilitate enough digestion to allow full spore viability and generates a variety of small and large cortex fragments. CwlJ1 is also sufficient to allow completion of nutrient-triggered germination independently and is a major factor in Ca 2+ -dipicolinic acid (DPA)-triggered germination, but its enzymatic activity remains unidentified because its products are large and not readily released from the spore's integuments. CwlJ2 contributes the least to overall cortex digestion but plays a subsidiary role in Ca 2+ -DPA-induced germination. SleL is an N -acetylglucosaminidase that plays the major role in hydrolyzing the large products of other GSLEs into small, rapidly released muropeptides. As the roles of these enzymes in cortex degradation become clearer, they will be targets for methods to stimulate premature germination of B. anthracis spores, greatly simplifying decontamination measures.