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Summary

Homologues of the E. coli chemotaxis (Che) signal transduction pathway are present in nearly all motile bacteria. Although E. coli contains only one Che cascade, many other bacteria are known to possess multiple sets of che genes. The role of multiple che-like gene clusters could potentially code for parallel Che-like signal transduction pathways that have distinctly different input and output functions. In this study, we describe a che-like gene cluster in Rhodospirillum centenum that controls a developmental cycle. In-frame deletion mutants of homologues of CheW (ΔcheW3aand ΔcheW3b), CheR (ΔcheR3), CheA (ΔcheA3) and a methyl-accepting chemotaxis protein (Δmcp3) are defective in starvation-induced formation of heat and desiccation resistant cyst cells. In contrast, mutants of homologues of CheY (ΔcheY3), CheB (ΔcheB3), and a second input kinase designated as CheS (ΔcheS3) result in cells that are derepressed in the formation of cysts. A model of signal transduction is presented in which there are three distinct Che-like signal transduction cascades; one that is involved in chemotaxis, one that is involved in flagella biosynthesis and the third that is involved in cyst development.