SosA inhibits cell division inStaphylococcus aureusin response to DNA damage

Abstract

Inhibition of cell division is critical for cell viability under DNA damaging conditions. In bacterial cells, DNA damage induces the SOS response, a process that inhibits cell division while repairs are being made. In coccoid bacteria, such as the human pathogen Staphylococcus aureus, the process remains poorly understood. Here we have characterized an SOS-induced cell-division inhibitor, SosA, in S. aureus. We find that in contrast to the wildtype, sosA mutant cells continue division under DNA damaging conditions with decreased viability as a consequence. Conversely, overproduction of SosA leads to cell division inhibition and reduced growth. The SosA protein is localized in the bacterial membrane and mutation of an extracellular amino acid, conserved between homologs of other staphylococcal species, abolished the inhibitory activity as did truncation of the C-terminal 30 amino acids. In contrast, C-terminal truncation of 10 amino acids lead to SosA accumulation and a strong cell division inhibitory activity. A similar phenotype was observed upon expression of wildtype SosA in a mutant lacking the membrane protease, CtpA. Thus, the extracellular C-terminus of SosA is required both for cell-division inhibition and for turnover of the protein. Functional studies showed that SosA is likely to interact with one or more divisome components and, without interfering with early cell-division events, halts cell division at a point where septum formation is initiated yet being unable to progress to septum closure. Our findings provide important insights into cell-division regulation in staphylococci that may foster development of new classes of antibiotics targeting this essential process.ImportanceStaphylococcus aureus is a serious human pathogen and a model organism for cell-division studies in spherical bacteria. We show that SosA is the DNA-damage-inducible cell-division inhibitor in S. aureus that upon expression causes cell swelling and cessation of the cell cycle at a characteristic stage post septum initiation but prior to division plate completion. SosA appears to function via an extracellular activity and is likely to do so by interfering with the essential membrane-associated division proteins, while at the same time being negatively regulated by the membrane protease CtpA. This report represents the first description of the process behind cell-division inhibition in coccoid bacteria. As several pathogens are included in this category, uncovering the molecular details of SosA activity and control can lead to identification of new targets for development of valuable anti-bacterial drugs.

DdcA antagonizes a bacterial DNA damage checkpoint

“…YneA is a membrane bound cell division inhibitor. This class of inhibitor in bacteria is typified as being a small protein that contains an N-terminal transmembrane domain, and they have been identified in several species (Kawai et al, 2003;Chauhan et al, 2006;Ogino et al, 2008;Modell et al, 2011;2014;Bojer et al, 2018). In C. crescentus, the cell division inhibitors SidA and DidA inhibit the activity of FtsW/N, which are components of the divisome.…”

“…In C. crescentus, the cell division inhibitors SidA and DidA inhibit the activity of FtsW/N, which are components of the divisome. A recent study in Staphylococcus aureus identified a small membrane division inhibitor, SosA, and its target appears to be PBP1 (Bojer et al, 2018), which is involved in peptidoglycan synthesis at the septum (Scheffers and Errington, 2004;Claessen et al, 2008). It is tempting to speculate that YneA could target an essential component of the cell division machinery, in particular because previous work found a conserved face of the transmembrane domain that was required for activity (Mo and Burkholder, 2010).…”

“…It is tempting to speculate that YneA could target an essential component of the cell division machinery, in particular because previous work found a conserved face of the transmembrane domain that was required for activity (Mo and Burkholder, 2010). Prior studies of C. crescentus and S. aureus were able to detect interactions between the cell division inhibitors and their targets using the bacterial two-hybrid assay (Modell et al, 2011;2014;Bojer et al, 2018). We reasoned that we might be able to identify an interacting partner of YneA or DdcA using this approach.…”

“…YneA has two major predicted features: an N-terminal transmembrane domain and a C-terminal LysM domain, and both have been found to be required for full activity (Mo and Burkholder, 2010). The other cell division inhibitors SidA, DidA, and SosA do not have a LysM domain (Modell et al, 2011;2014;Bojer et al, 2018). LysM domains bind to peptidoglycan (PG) and many proteins containing LysM domains have cell wall hydrolase activity (Buist et al, 2008).…”

DdcA antagonizes a bacterial DNA damage checkpoint

“…YneA is a membrane bound cell division inhibitor. This class of inhibitor in bacteria is typified as being a small protein that contains an N-terminal transmembrane domain, and they have been identified in several species [21, 28–31, 56]. In Caulobacter crescentus, the cell division inhibitors SidA and DidA inhibit the activity of FtsW/N, which are components of the divisome [30, 31].…”