Characterization of the Staphylococcus aureus heat shock, cold shock, stringent, and SOS responses and their effects on log-phase mRNA turnover

Abstract

Despite its being a leading cause of nosocomal and community-acquired infections, surprisingly little is known about Staphylococcus aureus stress responses. In the current study, Affymetrix S. aureus GeneChips were used to define transcriptome changes in response to cold shock, heat shock, stringent, and SOS response-inducing conditions. Additionally, the RNA turnover properties of each response were measured. Each stress response induced distinct biological processes, subsets of virulence factors, and antibiotic determinants. The results were validated by real-time PCR and stress-mediated changes in antimicrobial agent susceptibility. Collectively, many S. aureus stress-responsive functions are conserved across bacteria, whereas others are unique to the organism. Sets of small stable RNA molecules with no open reading frames were also components of each response. Induction of the stringent, cold shock, and heat shock responses dramatically stabilized most mRNA species. Correlations between mRNA turnover properties and transcript titers suggest that S. aureus stress response-dependent alterations in transcript abundances can, in part, be attributed to alterations in RNA stability. This phenomenon was not observed within SOS-responsive cells.

FIG. 1.

Global RNA turnover properties of S. aureus log-phase transcripts within untreated (mock) cells and under SOS response-, heat shock-, stringent response-, and cold shock-inducing conditions. RNA degradation properties of sigB-deficient cells are also plotted. Percentages of total transcripts with RNA half-lives of <2.5 min (gray bars), 2.5 to 5 min (white bars), 5 to 15 min (dotted bars), 15 to 30 min (hatched bars), and >30 min (widely hatched bars) are shown.

FIG. 2.

Stringent response-inducing conditions decrease S. aureus susceptibility to ciprofloxacin but not rifampin. The graphs show cell viabilities of unstressed (A) and mupirocin-treated (B) log-phase S. aureus UAMS-1 cells (0 h) in the absence (diamonds) or presence of either rifampin (triangles) or ciprofloxacin (squares). Cell viability was monitored for 4 h and then plotted.

FIG. 3.

Biological processes that are regulated in response to cold shock (A), heat shock (B), stringent response-inducing (C), and SOS response-inducing (D) conditions.