Phylogenetic analysis of photosynthetic genes of Rhodocyclus gelatinosus: Possibility of horizontal gene transfer in purple bacteria.

Nucleotide sequences of the genes coding for the M and cytochrome subunits of the photosynthetic reaction center of Rhodocyclus gelatinosus, a purple bacterium in the β subdivision, were determined. The deduced amino acid sequences of these proteins were compared with those of other photosynthetic bacteria. Based on the homology of these two photosynthetic proteins, Rc. gelatinosus was placed in the α subdivision of purple bacteria, which disagrees with the phylogenetic trees based on 16S rRNA and soluble cytochrome c 2. Horizontal transfer of the genes which code for the photosynthetic apparatus in purple bacteria can be postulated if the phylogenetic trees based on 16S rRNA and soluble cytochrome c 2 reflect the real history of purple bacteria.