Manganese And Zinc Regulate Virulence Determinants In Borrelia Burgdorferi

Borrelia burgdorferi, the causative agent of Lyme disease, must adapt to two diverse niches, an arthropod vector and a mammalian host. RpoS, an alternative sigma factor, plays a central role in spirochetal adaptation to the mammalian host by governing expression of many genes important for mammalian infection. B. burgdorferi is known to be unique in metal utilization, and little is known of the role of biologically available metals in B. burgdorferi. Here, we identified two transition metal ions, manganese (Mn2+) and zinc (Zn2+), that influenced regulation of RpoS. The intracellular Mn2+ level fluctuated approximately 20-fold under different conditions and inversely correlated with levels of RpoS and the major virulence factor OspC. Furthermore, an increase in intracellular Mn2+ repressed temperature-dependent induction of RpoS and OspC; this repression was overcome by an excess of Zn2+. Conversely, a decrease of intracellular Mn2+ by deletion of the Mn2+ transporter gene, bmtA, resulted in elevated levels of RpoS and OspC. Mn2+ affected RpoS through BosR, a Fur family homolog that is required for rpoS expression: elevated intracellular Mn2+ levels greatly reduced the level of BosR protein but not the level of bosR mRNA. Thus, Mn2+ and Zn2+ appeared to be important in modulation of the RpoS pathway that is essential to the life cycle of the Lyme disease spirochete. This finding supports the emerging notion that transition metals such as Mn2+ and Zn2+ play a critical role in regulation of virulence in bacteria.