Most bacteria have much more complex chemosensory systems than those of the extensively studied Escherichia coli. Rhodobacter sphaeroides, for example, has multiple homologues of the E. coli chemosensory proteins. The roles of these homologues have been extensively investigated using a combination of deletion, subcellular localization and phosphorylation assays. These studies have shown that the homologues have specific roles in the sensory pathway, and they differ in their cellular localization and interactions with other components of the pathway. The presence of multiple chemosensory pathways might enable bacteria to tune their tactic responses to different environmental conditions.