A cell wall protein (YqgA) is genetically related to the cell wall-degrading dl-endopeptidases in Bacillus subtilis

CwlQ Is Required for Swarming Motility but Not Flagellar Assembly in Bacillus subtilis

Lytic enzymes play an essential role in the remodeling of bacterial peptidoglycan (PG), an extracellular mesh-like structure that retains the membrane in the context of high internal osmotic pressure. Peptidoglycan must be unfailingly stable to preserve cell integrity, but must also be dynamically remodeled for the cell to grow, divide, and insert macromolecular machines. The flagellum is one such macromolecular machine that transits the PG, and flagellar insertion is aided by localized activity of a dedicated PG lyase in Gram-negative bacteria. To date, there is no known dedicated lyase in Gram-positive bacteria for the insertion of flagella. Here, we take a reverse-genetic candidate-gene approach and find that cells mutated for the lytic transglycosylase CwlQ exhibit a severe defect in flagellum-dependent swarming motility. We further show that CwlQ is expressed by the motility sigma factor SigD and is secreted by the type III secretion system housed inside the flagellum. Nonetheless, cells with mutations of CwlQ remain proficient for flagellar biosynthesis even when mutated in combination with four other lyases related to motility (LytC, LytD, LytF, and CwlO). The PG lyase (or lyases) essential for flagellar synthesis in B. subtilis, if any, remains unknown.IMPORTANCE Bacteria are surrounded by a wall of peptidoglycan and early work in Bacillus subtilis was the first to suggest that bacteria needed to enzymatically remodel the wall to permit insertion of the flagellum. No PG remodeling enzyme alone or in combination, however, has been found to be essential for flagellar assembly in B. subtilis Here, we take a reverse-genetic candidate-gene approach and find that the PG lytic transglycosylase CwlQ is required for swarming motility. Subsequent characterization determined that while CwlQ was coexpressed with motility genes and is secreted by the flagellar secretion apparatus, it was not required for flagellar synthesis. The PG lyase needed for flagellar assembly in B. subtilis remains unknown.

The "hole" story of predatory outer-membrane vesicles

All Gram-negative bacteria release membrane vesicles. These vesicles contain a cargo of proteins and enzymes that include one or more autolysins. Autolysins are a group of enzymes with specificity for the different linkages within peptidoglycan sacculi that if uncontrolled cause bacteriolysis. This minireview, written in honor and memory of Terry Beveridge, presents an overview of autolytic activity and focuses on Beveridge's important original observations regarding predatory membrane vesicles and their associated autolysin cargo.

New SigD-regulated genes identified in the rhizobacterium Bacillus amyloliquefaciens FZB42

The alternative sigma factor D is known to be involved in at least three biological processes in Bacilli: flagellin synthesis, methyl-accepting chemotaxis and autolysin synthesis. Although many Bacillus genes have been identified as SigD regulon, the list may be not be complete. With microarray-based systemic screening, we found a set of genes downregulated in the sigD knockout mutant of the plant growth-promoting rhizobacterium B. amyloliquefaciens subsp. plantarum FZB42. Eight genes (appA, blsA, dhaS, spoVG, yqgA, RBAM_004640, RBAM_018080 and ytk) were further confirmed by quantitative PCR and/or northern blot to be controlled by SigD at the transcriptional level. These genes are hitherto not reported to be controlled by SigD. Among them, four genes are of unknown function and two genes (RBAM_004640 and RBAM_018080), absent in the model strain B. subtilis 168, are unique to B. amyloliquefaciens stains. The eight genes are involved in sporulation, biofilm formation, metabolite transport and several other functions. These findings extend our knowledge of the regulatory network governed by SigD in Bacillus and will further help to decipher the roles of the genes.

Bacillus thuringiensis peptidoglycan hydrolase SleB171 involved in daughter cell separation during cell division

Whole-genome analyses have revealed a putative cell wall hydrolase gene (sleB171) that constitutes an operon with two other genes (ypeBandyhcN) of unknown function inBacillus thuringiensisBMB171. The putative SleB171 protein consists of 259 amino acids and has a molecular weight of 28.3 kDa. Gene disruption ofsleB171in the BMB171 genome causes the formation of long cell chains during the vegetative growth phase and delays spore formation and spore release, although it has no significant effect on cell growth and the ultimate release of the spores. The inseparable vegetative cells were nearly restored through the complementation ofsleB171expression. Real-time quantitative polymerase chain reaction analysis revealed thatsleB171is mainly active in the vegetative growth phase, with a maximum activity at the early stationary growth phase. Western blot analysis also confirmed thatsleB171is preferentially expressed during the vegetative growth phase. These results demonstrated that SleB171 plays an essential role in the daughter cell separation during cell division.