Analysis of the Borrelia burgdorferi Cyclic-di-GMP-Binding Protein PlzA Reveals a Role in Motility and Virulence
ABSTRACTThe cyclic-dimeric-GMP (c-di-GMP)-binding protein PilZ has been implicated in bacterial motility and pathogenesis. Although BB0733 (PlzA), the only PilZ domain-containing protein inBorrelia burgdorferi, was reported to bind c-di-GMP, neither its role in motility or virulence nor it's affinity for c-di-GMP has been reported. We determined that PlzA specifically binds c-di-GMP with high affinity (dissociation constant [Kd], 1.25 μM), consistent withKdvalues reported for c-di-GMP-binding proteins from other bacteria. Inactivation of the monocistronically transcribedplzAresulted in an opaque/solid colony morphology, whereas the wild-type colonies were translucent. While the swimming pattern of mutant cells appeared normal, on swarm plates, mutant cells exhibited a significantly reduced swarm diameter, demonstrating a role ofplzAin motility. Furthermore, theplzAmutant cells were significantly less infectious in experimental mice (as determined by 50% infectious dose [ID50]) relative to wild-type spirochetes. The mutant also had survival rates in fed ticks lower than those of the wild type. Consequently,plzAmutant cells failed to complete the mouse-tick-mouse infection cycle, indicatingplzAis essential for the enzootic life cycle ofB. burgdorferi. All of these defects were corrected when the mutant was complemented incis. We propose that failure ofplzAmutant cells to infect mice was due to altered motility; however, the possibility that an unidentified factor(s) contributed to interruption of theB. burgdorferienzootic life cycle cannot yet be excluded.