The N terminus of FliM is essential to promote flagellar rotation in Rhodobacter sphaeroides.

FliM is part of the flagellar switch complex. Interaction of this protein with phospho-CheY (CheY-P) through its N terminus constitutes the main information relay point between the chemotactic system and the flagellum. In this work, we evaluated the role of the N terminus of FliM in the swimming behavior of Rhodobacter sphaeroides. Strains expressing the FliM protein with substitutions in residues previously reported in Escherichia coli as being important for interaction with CheY showed an increased stop frequency compared with wild-type cells. In accordance, we observed that R. sphaeroides cells expressing FliM lacking either the first 13 or 20 amino acids from the N terminus showed a stopped phenotype. We show evidence that FliMDelta13 and FliMDelta20 are stable proteins and that cells expressing them allow flagellin export at levels indistinguishable from those detected for the wild-type strain. These results suggest that the N-terminal region of FliM is required to promote swimming in this bacterium. The role of CheY in controlling flagellar rotation in this organism is discussed.