Analysis of genes regulated by the peroxide response regulator PerR in Borrelia burgdorferi using real-time RT-PCR

Abstract

Borrelia burgdorferi sensu lato, the etiologic agent of Lyme disease, is a spirochetal bacterium that is transmitted to mammals via the bite of an Ixodes tick. The environments that the bacterium is exposed to when it resides in the tick and mammal are quite disparate and include differences in temperature, pH, and oxygen concentration. Although it has been shown that the aforementioned factors alter gene expression, few regulatory proteins have been identified in the B. burgdorferi genome. bb0647 encodes a peroxide response regulator (PerR) which regulates gene expression in response to oxidative stress in other organisms. Several borrelial genes with homology to known oxidative stress genes, and the pathogenesis-associated gene dbpA, contain putative PerR binding domains. To determine if PerR regulates the expression of oxidative stress genes in B. burgdorferi, we inactivated perR from a non-infectious B. burgdorferi strain (designated Lab), creating strain JS167. JS167 is hyper-resistant to reactive oxygen species and has increased superoxide dismutase activity compared to the Lab parental strain. JS167 makes four-fold more DbpA protein than Lab. We analyzed the expression of two oxidative stress genes, napA and sodA, and dbpA using real-time RT-PCR in JS167 and the infectious isolate MSK5 compared to Lab. We found napA and dbpA were induced 1.13-fold and 2.89-fold in JS167 compared to Lab, and sodA was induced 1.78-fold more in Lab than in JS167. The napA and sodA results indicate that the hyper-resistance of JS167 to reactive oxygen species is not due to the up-regulation of these two genes. MSK5 contains all known borrelial plasmids, and we therefore expect that gene expression be more tightly regulated in this strain compared to Lab. dbpA and sodA were expressed 3.48-fold and 1.25-fold more in Lab than in MSK5 and napA was expressed 1.38-fold more in MSK5. The low level of expression of dbpA in MSK5 does not correspond to DbpA protein levels in this isolate. Further studies addressing the effect of different oxygen concentrations and/or the presence of different oxidative stressors are needed to determine how these genes are regulated in response to oxidative stress.