Bacterial chemotaxis: Rhodobacter sphaeroides and Sinorhizobium meliloti - variations on a theme?

Chemotaxis in Rhodobacter sphaeroides and Sinorhizobium meliloti has a direct link to the environment in which a cell finds itself. The presence of at least two CheY homologues and the discovery that the swimming speed of these bacteria can vary indicate a different control mechanism at the flagellar motor. However, it remains to be understood why R sphaeroides should have at least two functional sets of genes encoding homologues of the enteric chemosensory pathway.