Characterization of a Major Photosynthesis Gene Cluster from the Heliobacterium Heliobacillus Mobilis

Abstract

Bacterial photosynthesis is found in five major eubacterial groups: cyanobacteria, purple bacteria, heliobacteria, green sulfur bacteria and green non-sulfur bacteria. Analysis of photosystems from purple and green non-sulfur bacteria indicates that these organisms synthesize primitive photosystems that are ancestral to the more complex oxygen evolving photosystem II (PSII) from cyanobacteria and chloroplasts (1). Additional studies of heliobacteria and green sulfur bacteria indicate that they synthesize photosystems that are ancestral to the photosystem I (PSI) complex from cyanobacteria and chloroplasts (2). With exception of sequence analysis of PSI and PSII structural polypeptides, there is little information on the origin and evolution of photosynthesis. Complete sequence information on photosynthesis genes is only available for the purple non-sulfur bacterium, Rhodobacter capsulatus, which has a major clustering of photosynthesis genes, and for the cyanobacterium Synechocystis sp. PCC 6803 for which the sequence of the entire chromosome has been completed. With the aim of providing more substantive information on the evolution of photosynthesis, we have undertaken an extensive characterization of photosynthesis genes from Heliobacillus mobilis and phylogenetic analysis based on the new sequence information, which provide insight for the origin and early evolutionary history of photosynthesis.