Methylation-independent and methylation-dependent chemotaxis in Rhodobacter sphaeroides and Rhodospirillum rubrum

In vivo and in vitro methylation, methanol production assays, and the use of specific antibodies raised against the sensory transducing protein Tar in Escherichia coli all failed to demonstrate the presence of methyl-accepting chemotaxis proteins (MCPs) in the photosynthetic bacterium Rhodobacter sphaeroides, although such proteins did exist in another photosynthetic bacterium, Rhodospirillum rubrum. The range of chemicals to which Rhodobacter sphaeroides responds, the lack of an all-or-none response, and the lack of true repellents indicate an alternative chemosensory pathway. The existence of MCPs in Rhodospirillum rubrum means that the lack of MCPs is not the result of a phototrophic metabolism, but may be connected to the unidirectional flagellar motor of Rhodobacter sphaeroides.