Insights into the complex regulation of rpoS in Borrelia burgdorferi

Co-ordinated regulation of gene expression is required for the transmission and survival of Borrelia burgdorferi in different hosts. The sigma factor RpoS (σS), as regulated by RpoN (σ54), has been shown to regulate key virulence factors (e.g. OspC) required for these processes. As important, multiple signals (e.g. temperature, pH, cell density, oxygen) have been shown to increase the expression of σS-dependent genes; however, little is known about the signal transduction mechanisms that modulate the expression of rpoS. In this report we show that: (i) rpoS has a σ54-dependent promoter that requires Rrp2 to activate transcription; (ii) Rrp2Δ123, a constitutively active form of Rrp2, activated σ54-dependent transcription of rpoS/P-lacZ reporter constructs in Escherichia coli; (iii) quantitative reverse transcription polymerase chain reaction (QRT-PCR) experiments with reporter cat constructs in B. burgdorferi indicated that Rrp2 activated transcription of rpoS in an enhancer-independent fashion; and finally, (iv) rpoN is required for cell density- and temperature-dependent expression of rpoS in B. burgdorferi, but histidine kinase Hk2, encoded by the gene immediately upstream of rrp2, is not essential. Based on these findings, a model for regulation of rpoS has been proposed which provides mechanisms for multiple signalling pathways to modulate the expression of the σS regulon in B. burgdorferi

Myositis during Borrelia burgdorferi infection (Lyme disease).

During the second stage of an illness caused by Borrelia burgdorferi, a young woman developed a myopathic syndrome characterised by severe muscular pains, incapacitating weakness of the proximal limb and the neck, as well as the bulbar muscles and elevated serum CK levels. Muscle biopsy revealed a non-inflammatory necrotising myopathy. B. burgdorferi infection was confirmed by a considerable rise of specific IgG antibodies. A course of high dose steroids alleviated the myalgias, but paresis began to improve only after treatment with antibiotics. Our observations confirm that B burgdorferi can cause, through an undertermined mechanism, a necrotising myopathy, in addition to the wide spectrum of already known neurological complications