Atypical transcriptional regulation by a histidine kinase in S. aureus

• Theresa Edery, Applied Molecular Biology & Biotechnology, University of Delaware

• Vijay Parashar, Medical and Molecular Sciences, University of Delaware

       Canonical two-component systems (TCSs) respond to environmental changes by regulating the transcriptional efficacy of target genes in bacteria. The KdpDE TCS senses salt stress and regulates potassium homeostasis and virulence in multiple bacteria. The histidine kinase (HK), KdpD, of this TCS senses extracellular potassium levels and regulates the expression of the potassium ion-channel KdpFABC and virulence factors that aid in host invasion and antibiotic resistance in Staphylococcus aureus. In addition to the canonical histidine kinase domains, KdpD also harbors an atypical N-terminal region (NTR) whose function has not been well characterized. Based on results from our laboratory, we hypothesize that KdpD-NTR interacts with RNA. In this project, we analyzed whether KdpD-NTR functions at the transcriptional or post-transcriptional levels to regulate RNA availability. Utilizing the rifampicin assay, which involves the use of the rifampicin antibiotic to inhibit transcription by targeting DNA-dependent RNA polymerase, we analyzed changes in the levels of RNAs involved in kdpFABC and virulence factors Aug, Spa, and HlgB in various strains of S. aureus deleted in the kdpDE operon and complemented with the kdpDE operon on a plasmid. Our rifampicin assay results show that upon salt stress, the KdpDE system increases the levels of the target RNAs largely independent of the canonical transcriptional regulation by TCSs. Furthermore, utilizing a KdpD mutant deficient in RNA binding, we demonstrate that RNA binding by KdpD significantly contributes to increased target RNA levels upon salt stress. We hypothesize that this post-transcriptional RNA binding by KdpD protects the RNAs from degradation by RNases. This newly identified post-transcriptional regulation by KdpD histidine kinases imparts stability to target RNAs, further enhancing the salt stress response in the cells.