Cava, F. | Search bioRxiv

bioRxiv2018

Agrobacterium tumefaciens divisome proteins regulate the transition from polar growth to cell division

The mechanisms that restrict peptidoglycan biosynthesis to the pole during elongation and re-direct peptidoglycan biosynthesis to mid-cell during cell division in polar-growing Alphaproteobacteria are largely unknown. Here, we demonstrate that although two of the three FtsZ homologs localize to mid-cell, exhibit GTPase activity and form co-polymers, only one, FtsZAT, is required for cell division. We find that FtsZAT is required not only for constriction and cell separation, but also for the termination of polar growth and regulation of peptidoglycan synthesis at mid-cell. Depletion of FtsZ in A. tumefaciens causes a striking phenotype: cells are extensively branched and accumulate growth active poles through tip splitting events. When cell division is blocked at a later stage, polar growth is terminated and ectopic growth poles emerge from mid-cell. Overall, this work suggests that A. tumefaciens FtsZ makes distinct contributions to the regulation of polar growth and cell division.

microbiology↗

bioRxiv2018

Endopeptidase regulation as a novel function of the Zur-dependent zinc starvation response

The cell wall is a strong, yet flexible, meshwork of peptidoglycan (PG) that gives a bacterium structural integrity. To accommodate a growing cell, the wall is remodeled by both PG synthesis and degradation. Vibrio cholerae encodes a group of three nearly identical zinc-dependent endopeptidases (EPs) that hydrolyze PG to facilitate cell growth. Two of these (shyA and shyC) are housekeeping genes and form a synthetic lethal pair, while the third (shyB) is not expressed under standard laboratory conditions. To investigate the role of ShyB, we conducted a transposon screen to identify mutations that activate shyB transcription. We found that shyB is induced as part of the Zur-mediated zinc starvation response, a mode of regulation not previously reported for cell wall lytic enzymes. In vivo, ShyB alone was sufficient to sustain cell growth in low-zinc environments. In vitro, ShyB retained its D,D-endopeptidase activity against purified sacculi in the presence of the metal chelator EDTA at a concentration that inhibits ShyA and ShyC. This suggests that ShyB can substitute for the other EPs during zinc starvation, a condition that pathogens encounter while infecting a human host. Our survey of transcriptomic data from diverse bacteria identified other candidate Zur-regulated endopeptidases, suggesting that this adaptation to zinc starvation is conserved in other Gram-negative bacteria.\n\nImportanceThe human host sequesters zinc and other essential metals in order to restrict growth of potentially harmful bacteria. In response, invading bacteria express a set of genes enabling them to cope with zinc starvation. In Vibrio cholerae, the causative agent of the diarrheal disease cholera, we have identified a novel member of this zinc starvation response: a cell wall hydrolase that retains function in low-zinc environments and is conditionally essential for cell growth. Other human pathogens contain homologs that appear to be under similar regulatory control. These findings are significant because they represent, to our knowledge, the first evidence that zinc homeostasis influences cell wall turnover. Anti-infective therapies commonly target the bacterial cell wall and, therefore, an improved understanding of how the cell wall adapts to host-induced zinc starvation could lead to new antibiotic development. Such therapeutic interventions are required to combat the rising threat of drug resistant infections.

microbiology↗