Abstract
Staphylococcus aureus is a Gram-positive bacterial pathogen of global concern and a leading cause of bacterial infections worldwide. Asymptomatic carriage of S. aureus on the skin and in the anterior nares is common and recognized as a predisposing factor to invasive infection. Transition of S. aureus from the carriage state to that of invasive infection is often accompanied by a temperature upshift from approximately 33°C to 37°C. Such a temperature shift is known in other pathogens to influence gene expression, often resulting in increased production of factors that promote survival or virulence within the host. One mechanism by which bacteria modulate gene expression in response to temperature is by the regulatory activity of RNA-based thermosensors, cis-acting riboregulators that control translation efficiency. This study was designed to identify and characterize RNA-based thermosensors in S. aureus. Initially predicted by in silico analyses of the S. aureus USA300 genome, reporter-based gene expression analyses and site-specific mutagenesis were performed to demonstrate the presence of a functional thermosensor within the 5’ UTR of cidA, a gene implicated in biofilm formation and survival of the pathogen. The nucleic sequence composing the identified thermosensor are sufficient to confer temperature-dependent post-transcriptional regulation, and activity is predictably altered by the introduction of site-specific mutations designed to stabilize or destabilize the structure within the identified thermosensor. The identified regulator is functional in both the native bacterial host S. aureus and in the distally related species Escherichia coli, suggesting that its regulatory activity is independent of host-specific factors. Interestingly, unlike the majority of bacterial RNA-based thermosensors characterized to date, the cidA thermosensor facilitates increased target gene expression at lower temperatures. In addition to the characterization of the first RNA-based thermosensor in the significant pathogen S. aureus, it highlights the diversity of function within this important class of ribo-regulators.
Highlights
Staphylococcus aureus is a Gram-positive pathogen that causes both nosocomial and community-acquired infections, ranging in severity from food poisoning and skin abscesses, to lifethreatening diseases such as pneumonia, meningitis, endocarditis, necrotizing fasciitis, and toxic shock syndrome [1, 2]
The remaining 10 putative thermosensors were prioritized based on the following criteria (i) belonging to the well-characterized family of FourU RNA thermometers (RNATs) [33], (ii) the likely SD is predicted to be within a hairpin structure, and (iii) a difference in the ΔG value of the predicted secondary structure at 25 ̊C and 37 ̊C, suggesting the presence of a temperature-responsive secondary structure (Table 2)
Essential to this designation are the findings that sequences within the cidA 5’ untranslated region (UTR) are sufficient to confer temperaturedependent post-transcriptional regulation (Figs 2 and 5), and that site-directed mutagenesis results in predictable alterations in regulatory activity (Figs 6 and 7)
Summary
Staphylococcus aureus is a Gram-positive pathogen that causes both nosocomial and community-acquired infections, ranging in severity from food poisoning and skin abscesses, to lifethreatening diseases such as pneumonia, meningitis, endocarditis, necrotizing fasciitis, and toxic shock syndrome [1, 2]. In contrast to the clinical presentation of severe invasive disease, S. aureus can be carried asymptomatically on the skin and in the anterior nares of the human host. Such carriage is common and considered a significant predisposing factor to invasive disease [8]. While extreme alterations in temperature can be deleterious to bacterial survival, more subtle changes in environmental temperature, such as that experienced by S. aureus during the transition from carriage to invasive disease, can represent an important environmental cue. When experienced by pathogenic bacteria, subtle shifts in environmental temperature often influence virulence gene expression [9,10,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
