A eukaryotic-like Ser/Thr kinase signals bacteria to exit dormancy in response to peptidoglycan fragments

Bacteria can respond to adverse environmental conditions by drastically reducing or even ceasing metabolic activity. They must then determine that conditions have improved before exiting dormancy, and one indication of such a change is the growth of other bacteria in the local environment. Growing bacteria release muropeptide fragments of the cell wall into the extracellular milieu, and we report here that these muropeptides are potent germinants of dormant Bacillus subtilis spores. The ability of a muropeptide to act as a germinant is determined by the identity of a single amino acid. A well-conserved, eukaryotic-like Ser/Thr membrane kinase containing an extracellular domain capable of binding peptidoglycan is necessary for this response, and a small molecule that stimulates related eukaryotic kinases is sufficient to induce germination. Another small molecule, staurosporine, that inhibits related eukaryotic kinases blocks muropeptide-dependent germination. Thus, in contrast to traditional antimicrobials that inhibit metabolically active cells, staurosporine acts by blocking germination of dormant spores.     

O-Acetylation of peptidoglycan is required for proper cell separation and S-layer anchoring in Bacillus anthracis

O-Acetylation of the MurNAc moiety of peptidoglycan is typically associated with bacterial resistance to lysozyme, a muramidase that serves as a central component of innate immunity. Here, we report that the peptidoglycan of Bacillus anthracis, the etiological agent of anthrax, is O-acetylated and that, unusually, this modification is produced by two unrelated families of O-acetyltransferases. Also, in contrast to other bacteria, O-acetylation of B. anthracis peptidoglycan is combined with N-deacetylation to confer resistance of cells to lysozyme. Activity of the Pat O-acetyltransferases is required for the separation of the daughter cells following bacterial division and for anchoring of one of the major S-layer proteins. Our results indicate that peptidoglycan O-acetylation modulates endogenous muramidase activity affecting the cell-surface properties and morphology of this important pathogen.     

Role of spore coat proteins in the resistance of Bacillus subtilis spores to Caenorhabditis elegans predation

Bacterial spores are resistant to a wide range of chemical and physical insults that are normally lethal for the vegetative form of the bacterium. While the integrity of the protein coat of the spore is crucial for spore survival in vitro, far less is known about how the coat provides protection in vivo against predation by ecologically relevant hosts. In particular, assays had characterized the in vitro resistance of spores to peptidoglycan-hydrolyzing enzymes like lysozyme that are also important effectors of innate immunity in a wide variety of hosts. Here, we use the bacteriovorous nematode Caenorhabditis elegans, a likely predator of Bacillus spores in the wild, to characterize the role of the spore coat in an ecologically relevant spore-host interaction. We found that ingested wild-type Bacillus subtilis spores were resistant to worm digestion, whereas vegetative forms of the bacterium were efficiently digested by the nematode. Using B. subtilis strains carrying mutations in spore coat genes, we observed a correlation between the degree of alteration of the spore coat assembly and the susceptibility to the worm degradation. Surprisingly, we found that the spores that were resistant to lysozyme in vitro can be sensitive to C. elegans digestion depending on the extent of the spore coat structure modifications.