'Green-like' and 'red-like' RubisCO cbbL genes in Rhodobacter azotoformans

We found that Rhodobacter azotoformans IFO 16436T contains two different cbbL genes coding form I ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) large subunits. One gene is located within a "green-like" group of the RubisCO phylogenetic tree, and the other is located within a "red-like" group. This is the first report that one organism contains both green-like and red-like RubisCO genes. Moreover, by PCR using primers which amplify two green-like and red-like cbbL genes alternatively and dot blot hybridization, we demonstrated that Rhodobacter blasticus, Rhodobacter capsulatus, and Rhodobacter veldkampii possess only green-like cbbL genes, and Rhodobacter sphaeroides possesses only a red-like cbbL gene. In the cbbL phylogenic analysis, R. spaeroides and R. azotoformans 1 (red-like) formed a cluster within the red-like group, and R. capsulatus, R. azotoformans 2 (green-like), R. blasticus, and R. veldkampii formed a cluster within the green-like group. This suggests that red-like cbbL genes of Rhodobacter species were derived from one ancestor, and green-like cbbL genes were derived from another ancestor. On the other hand, molecular phylogeny of the bacteria indicates that R. veldkampii, which has only a green-like cbbL gene, is the earliest evolved Rhodobacter species and that R. azotoformans and R. sphaeroides, which have red-like cbbL genes, are the latest evolved. Consequently, the following hypothesis is proposed: the common ancestor of Rhodobacter had a green-like cbbL gene, the common ancestor of R. azotoformans and R. sphaeroides subsequently obtained a red-like cbbL gene by a horizontal gene transfer, and the ancestor of R. sphaeroides later lost the green-like cbbL gene.