(), the agent of Lyme disease (LD), uses host-derived signals to modulate gene expression during the vector and mammalian phases of infection. Microarray analysis of mutants lacking orrelia host-aptation egulator (BadR) revealed down-regulation of genes encoding enzymes whose role in the patho-physiology of is unknown. Immunoblot analysis of the mutants confirmed reduced levels of these enzymes and one of these enzymes encoded by, shares homology to prokaryotic magnesium chelatase and Lon-type proteases. BB0086 levels were higher in under conditions mimicking fed ticks. Mutants lacking had no apparent growth defect but were incapable of colonizing immunocompetent C3H/HeN and immunodeficient SCID mice. Immunoblot analysis revealed reduced levels of proteins critical for adaptation of to the mammalian host such as OspC, DbpA and BBK32. Both RpoS and BosR - key regulators of gene expression in - were downregulated in the mutants. Therefore, we designated BB0086 as orrelia host-aptation rotein (BadP). Unlike mutants, the control strains established infection in C3H/HeN mice at 4 days post infection, indicating an early colonization defect in mutants due to reduced levels of lipoproteins/regulators critical for initial stages of infection. However, mutants survived within dialysis membrane chambers (DMCs) implanted within rat peritoneal cavity but unlike the control strains did not display complete switching of OspA to OspC suggesting incomplete adaptation to mammalian phase of infection. These findings have opened a novel regulatory mechanism, which impacts the virulence potential of.
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