Phylogenetic relationship of phototrophic purple sulfur bacteria according to pufL and pufM genes.

The phylogenetic relationship of purple sulfur bacteria (PSB), of the order Chromatiales (class Gammaproteobacteria), was analyzed based on photosynthetic gene sequences of the pufL and pufM genes, and the results compared to phylogenetic trees and groupings of the 16S rRNA gene. Primers for pufL and pufM genes were constructed and successfully used to amplify the pufLM genes of members of 16 genera of Chromatiales. In total, pufLM and 16S rRNA gene sequences of 66 PSB strains were analyzed, including 29 type strains and 28 new isolates. The inferred phylogenetic trees of the pufLM and 16S rRNA genes reflected a largely similar phylogenetic development suggesting coevolution of these essential genes within the PSB. It is concluded that horizontal gene transfer of pufLM genes within the PSB is highly unlikely, in contrast to the situation in other groups of anoxygenic phototrophic bacteria belonging to Alpha- and Betaproteobacteria. The phylogeny of pufLM is therefore in good agreement with the current taxonomic classification of PSB. A phylogenetic classification of PSB to the genus level is possible based on their pufL or pufM sequences, and in many cases even to the species level. In addition, our data support a correlation between Puf protein structure and the type of internal photosynthetic membranes (vesicular, lamellar, or tubular).