Positive Regulation of Leptospira interrogans kdp Expression by KdpE as Demonstrated with a Novel β-Galactosidase Reporter in Leptospira biflexa

Leptospirosis is a potentially deadly zoonotic disease that afflicts humans and animals.Leptospira interrogans , the predominant agent of leptospirosis, encounters diverse conditions as it proceeds through its life cycle, which includes stages inside and outside the host. Unfortunately, the number of genetic tools available for examining the regulation of gene expression inL. interrogans is limited. Consequently, little is known about the genetic circuits that control gene expression inLeptospira . To better understand the regulation of leptospiral gene expression, theL. interrogans kdp locus, encoding homologs of the P-type ATPase KdpABC potassium transporter with their KdpD sensors and KdpE response regulators, was selected for analysis. We showed that akdpE mutation inL. interrogans prevented the increase inkdpABC mRNA levels observed in the wild-typeL. interrogans strain when external potassium levels were low. To confirm that KdpE was a positive regulator ofkdpABC transcription, we developed a novel approach for constructing chromosomal genetic fusions to the endogenousbgaL (β-galactosidase) gene of the nonpathogenLeptospira biflexa . We demonstrated positive regulation of akdpA′-bgaL fusion inL. biflexa by theL. interrogans KdpE response regulator. A controllipL32′-bgaL fusion was not regulated by KdpE. These results demonstrate the utility of genetic fusions to thebgaL gene ofL. biflexa for examining leptospiral gene regulation.