Abstract
ABSTRACTStaphylococcus aureusexhibits an unusually high level of osmotolerance and Na+tolerance, properties that support survival in various host niches and in preserved foods. The genetic basis of these traits is not well understood. We compared the transcriptional profiles ofS. aureusgrown in complex medium with and without 2 M NaCl. The stimulon for growth in high-osmolality media and Na+included genes involved in uptake of K+, other compatible solutes, sialic acid, and sugars; capsule biosynthesis; and amino acid and central metabolism. Quantitative PCR analysis revealed that the loci responded differently from each other to high osmolality imposed by elevated NaCl versus sucrose. High-affinity K+uptake (kdp) genes and capsule biosynthesis (cap5) genes required the two-component system KdpDE for full induction by osmotic stress, withkdpAinduced more by NaCl andcap5Binduced more by sucrose. Focusing on K+importers, we identified threeS. aureus genes belonging to the lower-affinity Trk/Ktr family that encode two membrane proteins (KtrB and KtrD) and one accessory protein (KtrC). In the absence of osmotic stress, thektrgene transcripts were much more abundant than thekdpAtranscript. Disruption ofS. aureus kdpAcaused a growth defect under low-K+conditions, disruption ofktrCresulted in a significant defect in 2 M NaCl, and a ΔktrCΔkdpAdouble mutant exhibited both phenotypes. Protective effects ofS. aureusKtr transporters at elevated NaCl are consistent with previous indications that both Na+and osmolality challenges are mitigated by the maintenance of a high cytoplasmic K+concentration.IMPORTANCEThere is general agreement that the osmotolerance and Na+tolerance ofStaphylococcus aureusare unusually high for a nonhalophile and support its capacity for human colonization, pathogenesis, and growth in food. Nonetheless, the molecular basis for these properties is not well defined. The genome-wide response ofS. aureusto a high concentration, 2 M, of NaCl revealed the upregulation of expected genes, such as those for transporters of compatible solutes that are widely implicated in supporting osmotolerance. A high-affinity potassium uptake system, KdpFABC, was upregulated, although it generally plays a physiological role under very low K+conditions. At higher K+concentrations, a lower-affinity and more highly expressed type of K+transporter system, Ktr transporters, was shown to play a significant role in high Na+tolerance. This study illustrates the importance of the K+status of the cell for tolerance of Na+byS. aureusand underscores the importance of monovalent cation cycles in this pathogen.
There is general agreement that the osmotolerance and Na+tolerance ofStaphylococcus aureusare unusually high for a nonhalophile and support its capacity for human colonization, pathogenesis, and growth in food. Nonetheless, the molecular basis for these properties is not well defined. The genome-wide response ofS. aureusto a high concentration, 2 M, of NaCl revealed the upregulation of expected genes, such as those for transporters of compatible solutes that are widely implicated in supporting osmotolerance. A high-affinity potassium uptake system, KdpFABC, was upregulated, although it generally plays a physiological role under very low K+conditions. At higher K+concentrations, a lower-affinity and more highly expressed type of K+transporter system, Ktr transporters, was shown to play a significant role in high Na+tolerance. This study illustrates the importance of the K+status of the cell for tolerance of Na+byS. aureusand underscores the importance of monovalent cation cycles in this pathogen.