Identification of a fourth cheY gene in Rhodobacter sphaeroides and interspecies interaction within the bacterial chemotaxis signal transduction pathway

The Escherichia coli chemotaxis signal transduction pathway has: CheA, a hi stidine protein kinase; CheW, a linker between CheA and sensory proteins; C heY, the effector; and CheZ, a signal terminator. Rhodobacter sphaeroides h as multiple copies of these proteins (2x CheA, 3x CheW and 3x CheY, but no CheZ), In this study, we found a fourth cheY and expressed these R. sphaero ides proteins in E. coli. CheA2 (but not CheA1) restored swarming to an E, coli cheA mutant (RP9535), CheW3 (but not CheW2) restored swarming to a che W mutant of E, coli (RP4606), R, sphaeroides CheYs did not affect E, coli l acking CheY, but restored swarming to a cheZ strain (RP1616), indicating th at they can act as signal terminators in E. coli, An E, coli CheY, which is phosphorylated but cannot bind the motor (CheY109KR), was expressed in RP1 616 but had no effect, Overexpression of CheA2, CheW2, CheW3, CheY1, CheY3 and CheY4 inhibited chemotaxis of wild-type E, coli (RP437) by increasing i ts smooth-swimming bias. While some R, sphaeroides proteins restore tumblin g to smooth-swimming E, coli mutants, their activity is not controlled by t he chemosensory receptors, R, sphaeroides possesses a phosphorelay cascade compatible with that of E, coli, but has additional incompatible homologues .