Transcriptional interplay among the regulators Rrp2, RpoN and RpoS in Borrelia burgdorferi

Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA Correspondence Michael V. Norgard michael.norgard{at}utsouthwestern.edu The RpoN–RpoS alternative sigma factor pathway is essential for key adaptive responses by Borrelia burgdorferi , particularly those involved in the infection of a mammalian host. A putative response regulator, Rrp2, is ostensibly required for activation of the RpoN-dependent transcription of rpoS . However, questions remain regarding the extent to which the three major constituents of this pathway (Rrp2, RpoN and RpoS) act interdependently. To assess the functional interplay between Rrp2, RpoN and RpoS, we employed microarray analyses to compare gene expression levels in rrp2 , rpoN and rpoS mutants of parental strain 297. We identified 98 genes that were similarly regulated by Rrp2, RpoN and RpoS, and an additional 47 genes were determined to be likely regulated by this pathway. The substantial overlap between genes regulated by RpoS and RpoN provides compelling evidence that these two alternative sigma factors form a congruous pathway and that RpoN regulates B. burgdorferi gene expression through RpoS. Although several known B. burgdorferi virulence determinants were regulated by the RpoN–RpoS pathway, a defined function has yet to be ascribed to most of the genes substantially regulated by Rrp2, RpoN and RpoS. Abbreviations: DMC, dialysis membrane chamber; qRT-PCR, real-time quantitative RT-PCR These authors contributed equally to this work. The array data discussed in this paper have been deposited in the NCBI Gene Expression Omnibus (GEO; http://www.ncbi.nlm.nih.gov/geo/ ) and are accessible through GEO series accession number GSM284306–284322. A supplementary table listing the oligonucleotide primers used in this study and two supplementary figures showing representative scanned microarray images of 1723 B. burgdorferi ORFs are available with the online version of this paper.