Two CheW coupling proteins are essential in a chemosensory pathway of Borrelia burgdorferi

In the model organism Escherichia coli, the coupling protein CheW, which bridges the chemoreceptors and histidine kinase CheA, is essential for chemotaxis. Unlike the situation in E. coli, Borrelia burgdorferi, the causative agent of Lyme disease, has three cheW homologues (cheW(1) , cheW(2) and cheW(3) ). Here, a comprehensive approach is utilized to investigate the roles of the three cheWs in chemotaxis of B. burgdorferi. First, genetic studies indicated that both the cheW(1) and cheW(3) genes are essential for chemotaxis, as the mutants had altered swimming behaviours and were non-chemotactic. Second, immunofluorescence and cryo-electron tomography studies suggested that both CheW(1) and CheW(3) are involved in the assembly of chemoreceptor arrays at the cell poles. In contrast to cheW(1) and cheW(3) , cheW(2) is dispensable for chemotaxis and assembly of the chemoreceptor arrays. Finally, immunoprecipitation studies demonstrated that the three CheWs interact with different CheAs: CheW(1) and CheW(3) interact with CheA(2) whereas CheW(2) binds to CheA(1) . Collectively, our results indicate that CheW(1) and CheW(3) are incorporated into one chemosensory pathway that is essential for B. burgdorferi chemotaxis. Although many bacteria have more than one homologue of CheW, to our knowledge, this report provides the first experimental evidence that two CheW proteins coexist in one chemosensory pathway and that both are essential for chemotaxis.