The FUR-like regulators PerRA and PerRB control a complex signaling network required for mammalian host-adaptation and virulence of Leptospira interrogans

Leptospira interrogans, the causative agent of most cases of human leptospirosis, must respond to myriad environmental signals during its free-living and pathogenic lifestyles. Previously, we compared L. interrogans cultivated in vitro and in vivo using a dialysis membrane chamber (DMC) peritoneal implant model. From these studies emerged 166 genes that were differentially regulated in response to host signals, including perRA, one of two Peroxide stress response (PerR)-like regulators encoded by L. interrogans. Zavala-Alvarado et al. recently demonstrated that leptospires lacking both PerRA and PerRB are avirulent in hamsters. Herein, we establish that PerRA and PerRB also are required for renal colonization in C3H/HeJ mice. The finding that loss of virulence was observed only with the perRA/B double mutant suggests that these regulators serve redundant or overlapping functions in vivo. Our finding that the perRA/B double mutant survives at wild-type levels in DMCs is noteworthy as it demonstrates that the loss of virulence is not due to a metabolic lesion (i.e., metal starvation) but instead reflects dysregulation of virulence-related gene products. Comparative RNA-Seq analyses of perRA, perRB and perRA/B mutants cultivated within DMCs identified 106 genes that are dysregulated in the double mutant, including ligA, ligB and lvrA/B sensory histidine kinases. Decreased expression of LigA and LigB in the perRA/B mutant was not due to loss of LvrAB signal transduction. The majority of genes in the perRA and perRB single and double mutant DMC regulons were differentially expressed only in vivo, highlighting the importance of host-specific signals for regulating gene expression in L. interrogans. Importantly, the PerRA, PerRB and PerRA/B DMC regulons each contain multiple genes related to environmental sensing and/or transcriptional regulation. Collectively, our data suggest that PerRA and PerRB are part of a complex signaling network required by L. interrogans for adaptation to and survival within the host.Author SummaryLeptospirosis is a neglected tropical disease with a worldwide distribution. Globally, ∼1 million cases and ∼60,000 deaths are reported each year. The majority of cases of human leptospirosis are associated with Leptospira interrogans. Infection begins when a naïve reservoir (or incidental) host comes into direct or indirect contact with urine from an infected reservoir host. While infection in reservoir hosts, including rats and mice, is generally asymptomatic, incidental hosts, including humans, may develop clinical symptoms ranging from mild flu-like illness to fulminant disease. The gene products required by leptospires for infection remain poorly understood. Herein, we establish that the FUR family regulators PerRA and PerRB function either cooperatively or in parallel to promote survival and renal colonization in mice. By comparative transcriptomics, we identified >100 genes that were dysregulated in the perRA/B double mutant in vivo, including four virulence-related genes. Importantly, the PerRA, PerRB and PerRA/B DMC regulons contain multiple genes related to environmental sensing and/or transcriptional regulation. Our data suggest that PerRA and PerRB are part of a complex signaling network required by L. interrogans for adaptation to and survival within the host.