Rhodopseudomonas palustris Genome sequencing

Many photosynthetic bacteria have peripheral light harvesting (LH) antenna complexes that increase the efficiency of light energy capture. These have been studied extensively in the purple nonsulfur photosynthetic bacterium Rhodopseudomonas palustris. This group of bacteria are models for studies of photosynthesis because they have much simpler systems of light energy conversion than do green plants or cyanobacteria. R. palustris produces different types of LH complexes under high light intensities (LH2 complex) and low light intensities (LH3 and LH4 complex). There are multiple pucBA operons that encode the a and ß peptides that make up these complexes, whose expression is affected by light intensity. However, low-resolution structures, amino acid similarities between the complexes, and a lack of transcriptional analysis have made it difficult to determine the contribution of different pucBA operons to the composition and function of different LH complexes under different light intensities. It was also unclear how much diversity of the R. palustris LH complexes exists in nature. To gain insight into the composition of the LH complexes under high and low light intensities, and their prevalence in the environment we undertook an integrative genomics approach using sequenced R. palustris strains. Analysis of the gene content of the strains revealed that even closely related R. palustris strains had differences in their pucBA gene content. The variation observed in LH gene composition in environmental isolates of R. palustris likely reflects how these strains have adapted to specific light conditions in the environment.