The FUR-like regulators PerRA and PerRB integrate a complex regulatory network that promotes mammalian host-adaptation and virulence of Leptospira interrogans

Abstract

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 160 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 only 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 DMC regulons was 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.

The oxidative stress response of pathogenic Leptospira is controlled by two peroxide stress regulators which putatively cooperate in controlling virulence

“…Moreover, several differentially-expressed ORFs of unknown function could also be responsible for the loss of virulence of the double perRAperRB mutant. It is noteworthy that the double perRAperRB mutant was also unable to colonize mice [57] and, consistent with what is observed with in vitro -cultivated perRAperRB mutant, this correlated with dramatic gene dysregulation including down-regulation of ligA and ligB [57].…”

“…The distinct repartition of PerRA and PerRB in the Leptospira genus and differences in their respective regulon support the hypothesis of a non-redundant function in the adaptation to oxidative stress. The PerRA and PerRB regulons determined when L. interrogans are cultivated inside a host using DMC implemented in rats confirmed the limited overlap between PerRA and PerRB regulons [57].…”

“…Moreover, the exclusive presence of PerRB in the pathogenic Leptospira clades strongly suggests that PerRB function is more related to regulating adaptation to infection-related conditions rather than to environmental survival. Very interestingly, when the perRB mutant was cultivated in the host conditions using the DMC implants, a higher number of genes were differentially-expressed with greater fold changes than when the perRB mutant was cultivated at 30°C in the laboratory conditions [57]. Notably, in the host condition, the absence of perRB also led to the deregulation of several genes involved in signaling and regulation, which is consistent with a role of PerRB in regulating adaptation to the host environment [57].…”