Comparative and Functional Genomics of Anoxygenic Green Bacteria from the Taxa Chlorobi, Chloroflexi, and Acidobacteria

Abstract

Green bacteria are a diverse group of chlorophototrophic organisms belonging to three major taxa within the domain Bacteria: Chlorobi, Chloroflexi, and Acidobacteria. Most, although not all, of these organisms synthesize bacteriochlorophylls c, d or e and utilize chlorosomes for light harvesting. The pace of discoveries concerning the metabolism and physiology of these bacteria has accelerated rapidly since completion of the sequencing of the genomes of the green sulfur bacterium Chlorobaculum tepidum and the filamentous anoxygenic phototroph, Chloroflexus aurantiacus. This chapter summarizes insights gained from the extensive genome sequence data for members of these three taxa. The discovery of the first chlorophototrophic member of the phylum Acidobacteria, Candidatus Chloracidobacterium thermophilum, is also described, and recent insights into the physiology and metabolism of this unique, aerobic photoheterotroph are presented. Based upon phylogenetic inferences derived from analyses of sequences for reaction centers and enzymes of (bacterio)chlorophyll biosynthesis, some implications concerning the evolutionary origins of photosynthesis are discussed.