TheStaphylococcus aureussmall non-coding RNA IsrR regulates TCA cycle activity and virulence

Abstract

AbstractStaphylococcus aureushas evolved mechanisms to cope with low iron (Fe) availability in host tissues.S. aureususes the ferric uptake transcriptional regulator (Fur) to sense titers of cytosolic Fe. Upon Fe depletion, apo-Fur relieves transcriptional repression of genes utilized for Fe uptake. We demonstrate that anS. aureusΔfurmutant has decreased expression ofacnA, which codes for the Fe-dependent enzyme aconitase. DecreasedacnAexpression prevented the Δfurmutant from growing with amino acids as sole carbon and energy sources. Suppressor analysis determined that a mutation inisrR, which produces a regulatory RNA, permitted growth by decreasingisrRtranscription. The decreased AcnA activity of the Δfurmutant was partially relieved by an ΔisrRmutation. Directed mutation of bases predicted to facilitate the interaction between theacnAtranscript and IsrR, decreased the ability of IsrR to controlacnAexpressionin vivoand IsrR bound to theacnAtranscriptin vitro. IsrR also bound to the transcripts coding the alternate TCA cycle proteinssdhC,mqo,citZ, andcitM. Whole cell metal analyses suggest that IsrR promotes Fe uptake and increases intracellular Fe not ligated by macromolecules. Lastly, we determined that Fur and IsrR promote infection using murine skin and acute pneumonia models.Graphical Abstract