RpoS Is Not Central to the General Stress Response inBorrelia burgdorferibut Does Control Expression of One or More Essential Virulence Determinants

Abstract

Borrelia burgdorferi, the Lyme disease spirochete, undergoes dramatic changes in antigenic composition as it cycles between its arthropod and mammalian hosts. A growing body of evidence suggests that these changes reflect, at least in part, the need for spirochetes to adapt to the physiological stresses imposed by abrupt changes in environmental conditions and nutrient availability. -PCR), we demonstrated that, in contrast to its ortholog (rpoS Ec ) in Escherichia coli, rpoS Bb was expressed at significant levels in B. burgdorferi throughout all phases of growth following temperature shift. By comparing a B. burgdorferi strain 297 rpoS Bb mutant to its wild-type counterpart, we determined that RpoS Bb was not required for survival following exposure to a wide range of environmental stresses (i.e., temperature shift, serum starvation, increased osmolality, reactive oxygen intermediates, and increased or reduced oxygen tension), although the mutant was more sensitive to extremes of pH. While B. burgdorferi strains lacking RpoS were able to survive within intraperitoneal dialysis membrane chambers at a level equivalent to that of the wild type, they were avirulent in mice. Lastly, RT-PCR analysis of the ospE-ospF-elp paralogous lipoprotein families complements earlier findings that many temperature-inducible borrelial loci are controlled in an RpoS Bbindependent manner. Together, these data point to fundamental differences between the role(s) of RpoS in B. burgdorferi and that in E. coli. Rather than functioning as a master regulator, RpoS Bb appears to serve as a stress-responsive activator of a subset of virulence determinants that, together with the RpoS-independent, differentially expressed regulon, encompass the spirochete's genetic programs required for mammalian host adaptation.

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

“…In contrast, no spirochaetes were recovered from samples of mice inoculated with the rrp2, rpoN or rpoS mutants. Notably, whereas rpoN and rpoS mutants of B. burgdorferi have been reported to be noninfectious for mice (Caimano et al, 2004;Fisher et al, 2005), this is the first study, to our knowledge, to show that an rrp2 mutant also lacks the ability to infect mice. These results indicate that all three regulators are required by B. burgdorferi to infect mammals.…”

“…Along these lines, our laboratory and others have previously reported the existence in B. burgdorferi of an alternative sigma factor (RpoN/s 54 -RpoS/s S ) regulatory cascade that governs the expression of outer surface (lipo)protein C (OspC), decorin-binding protein A (DbpA), multicopy lipoprotein-8 (Mlp8), fibronectinbinding protein BBK32, and other potential virulenceassociated proteins (Caimano et al, 2004(Caimano et al, , 2005(Caimano et al, , 2007Fisher et al, 2005;He et al, 2007;Hubner et al, 2001;Smith et al, 2007;Yang et al, 2003aYang et al, , b, 2005. In this regulatory pathway, Rrp2, a putative response regulator (enhancer-binding protein) of a two-component sensory transduction system, is likely activated via phosphorylation through a histidine kinase (Hk2) (Fraser et al, 1997;Yang et al, 2003a).…”

Sigma cascades in prokaryotic regulatory networks

“…Both N -and S -deficient B. burgdorferi mutants are avirulent in mice (8,10), and N was shown in the present study to be required for the entry of the spirochete into tick salivary glands as well, implying a role in the transmission of Lyme disease. Neither sigma factor was essential for growth in culture medium, consistent with the notion that these regulons are primarily involved in stress responses.…”

bptA(bbe16) is essential for the persistence of the Lyme disease spirochete,Borrelia burgdorferi, in its natural tick vector

“…Whereas many of these differentially regulated genes likely represent physiological ''housekeeping'' genes typically not thought of as virulenceassociated, others have been noted in separate studies to encode virulence factors essential for Bb's infection of or survival within its arthropod or mammalian hosts (6,7,33,(43)(44)(45). Nevertheless, the testing of Koch's molecular postulates to ascertain whether a gene encodes a virulence trait (46) has been hindered greatly by a paucity of systems for genetically manipulating virulent Bb (13,14).…”