A che-like signal transduction cascade involved in controlling flagella biosynthesis in Rhodospirillum centenum

Rhodospirillum centenum is a photosynthetic bacterium capable of undergoing swim cell to swarm cell differentiation that allows this species to be motile on both liquid and solid media. Previous experiments have demonstrated that the che1 operon is required for the control of chemotactic and phototactic behaviour of both swim and swarm cells. In this report, we analyse the function of a second che-like gene cluster in R. centenum, the che2 gene cluster. In-frame deletion mutants of cheW2, cheB2, cheR2, cheY2, and of the entire che2 operon, exhibit defects in swim and swarm cell motility. Analysis of these strains demonstrates that they are non-motile, and that the non-motile phenotype is resulting from reduced polar and lateral flagella synthesis. Additionally, mutations in mcp2, ORF204, cheA2 and ORF74 remain chemotacticly and phototacticly competent at both high and low growth temperatures. Mutations in these che2 genes result in elevated levels of flagellin proteins giving rise to a hyperflagellate phenotype. We propose a model in which R. centenum utilizes a che-like signal transduction pathway (che2) for regulating flagellum synthesis in order to optimize swim cell-swarm cell differentiation in response to changing environmental conditions.