Molecular evidence for the early evolution of photosynthesis

The origin and evolution of photosynthesis have Long remained enigmatic due to a Lack of sequence information of photosynthesis genes across the entir e photosynthetic domain. To probe early evolutionary history of photosynthe sis, we obtained new sequence information of a number of photosynthesis gen es from the green sulfur bacterium Chlorobium tepidum and the green nonsulf ur bacterium Chloroflexus aurantiacus. A total of 31 open reading frames th at encode enzymes involved in bacteriochlorophyll/porphyrin biosynthesis, c arotenoid biosynthesis, and photosynthetic electron transfer were identifie d in about 100 kilobase pairs of genomic sequence. Phylogenetic analyses of multiple magnesium-tetrapyrrole biosynthesis genes using a combination of distance, maximum parsimony, and maximum likelihood methods indicate that h eliobacteria are closest to the Last common ancestor of all oxygenic photos ynthetic Lineages and that green sulfur bacteria and green nonsulfur bacter ia are each other's closest relatives. Parsimony and distance analyses furt her identify purple bacteria as the earliest emerging photosynthetic Lineag e. These results challenge previous conclusions based on 16S ribosomal RNA and Hsp60/Hsp70 analyses that green nonsulfur bacteria or heliobacteria are the earliest phototrophs. The overall consensus of our phylogenetic analys is, that bacteriochlorophyll biosynthesis evolved before chlorophyll biosyn thesis, also argues against the long-held Granick hypothesis.