SrrAB Modulates Staphylococcus aureus Cell Death through Regulation of cidABC Transcription

Abstract

The death and lysis of a subpopulation in Staphylococcus aureus biofilm cells are thought to benefit the surviving population by releasing extracellular DNA, a critical component of the biofilm extracellular matrix. Although the means by which S. aureus controls cell death and lysis is not understood, studies implicate the role of the cidABC and lrgAB operons in this process. Recently, disruption of the srrAB regulatory locus was found to cause increased cell death during biofilm development, likely as a result of the sensitivity of this mutant to hypoxic growth. In the current study, we extended these findings by demonstrating that cell death in the ⌬srrAB mutant is dependent on expression of the cidABC operon. The effect of cidABC expression resulted in the generation of increased reactive oxygen species (ROS) accumulation and was independent of acetate production. Interestingly, consistently with previous studies, cidC-encoded pyruvate oxidase was found to be important for the generation of acetic acid, which initiates the cell death process. However, these studies also revealed for the first time an important role of the cidB gene in cell death, as disruption of cidB in the ⌬srrAB mutant background decreased ROS generation and cell death in a cidCindependent manner. The cidB mutation also caused decreased sensitivity to hydrogen peroxide, which suggests a complex role for this system in ROS metabolism. Overall, the results of this study provide further insight into the function of the cidABC operon in cell death and reveal its contribution to the oxidative stress response. IMPORTANCEThe manuscript focuses on cell death mechanisms in Staphylococcus aureus and provides important new insights into the genes involved in this ill-defined process. By exploring the cause of increased stationary-phase death in an S. aureus ⌬srrAB regulatory mutant, we found that the decreased viability of this mutant was a consequence of the overexpression of the cidABC operon, previously shown to be a key mediator of cell death. These investigations highlight the role of the cidB gene in the death process and the accumulation of reactive oxygen species. Overall, the results of this study are the first to demonstrate a positive role for CidB in cell death and to provide an important paradigm for understanding this process in all bacteria.

The LysR‐type transcriptional regulator, CidR, regulates stationary phase cell death in Staphylococcus aureus

“…Recent studies in our laboratory have also pointed to CidB as the primary effector of cell death in this system. In these studies, we observed that the increased stationary phase cell death associated with a srrAB mutation was dependent on de‐repression of cidABC in this mutant (Windham et al ., ). Interestingly, increased cidABC expression in the srrAB mutant did not result in increased production of acetate, consistent with a role for CidA in countering CidC activity.…”

“…Double chromosomal mutations in the Δ pta and Δ ackA genetic backgrounds were generated by phi11‐mediated phage transduction. Previously, we reported the construction of Δ cidA and Δ cidB mutants (Windham et al ., ) The cidC gene was sequenced from both Δ cidA and Δ cidB mutants to confirm the absence of any polar effects that may have occurred during the gene deletion process. The cidAB mutant was constructed by amplifying the cidB deletion from KB1060 and ligating into pJB60, which contains the upstream of cidA (Windham et al , ).…”

Impaired respiration elicits SrrAB-dependent programmed cell lysis and biofilm formation in Staphylococcus aureus

“…This role was predicated upon the phenotype of a cidA mutant; however, recent studies suggest that this was likely an outcome of a secondary mutation (Rice et al, 2007; Chaudhari et al, 2016). CidB, is predicted to be a membrane-associated protein, however its precise function and biochemical activity(s) are yet to be defined (Rice et al, 2003; Windham et al, 2016; Chaudhari et al, 2016). In our hands, cidA::Tn , cidB::Tn , and lrgA::Tn strains were not attenuated in fermentative biofilm formation suggesting a functional separation of the S. aureus PCD and PCL pathways, with respect to biofilm formation.…”

The Staphylococcus aureus SrrAB Regulatory System Modulates Hydrogen Peroxide Resistance Factors, Which Imparts Protection to Aconitase during Aerobic Growth

“…While this manuscript was under preparation, a study was published investigating the influence of SrrAB upon programmed cell death mediated by cidABC [63]. The study used a special medium (TSB medium amended with 35 mM glucose) that induces cell death phenotypes [63].…”

“…The study used a special medium (TSB medium amended with 35 mM glucose) that induces cell death phenotypes [63]. The authors found that SrrAB represses the transcription of cidABC when cultured in the cell death media.…”