Complete genome sequence of the filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus

Abstract

BackgroundChloroflexus aurantiacus is a thermophilic filamentous anoxygenic phototrophic (FAP) bacterium, and can grow phototrophically under anaerobic conditions or chemotrophically under aerobic and dark conditions. According to 16S rRNA analysis, Chloroflexi species are the earliest branching bacteria capable of photosynthesis, and Cfl. aurantiacus has been long regarded as a key organism to resolve the obscurity of the origin and early evolution of photosynthesis. Cfl. aurantiacus contains a chimeric photosystem that comprises some characters of green sulfur bacteria and purple photosynthetic bacteria, and also has some unique electron transport proteins compared to other photosynthetic bacteria.MethodsThe complete genomic sequence of Cfl. aurantiacus has been determined, analyzed and compared to the genomes of other photosynthetic bacteria.ResultsAbundant genomic evidence suggests that there have been numerous gene adaptations/replacements in Cfl. aurantiacus to facilitate life under both anaerobic and aerobic conditions, including duplicate genes and gene clusters for the alternative complex III (ACIII), auracyanin and NADH:quinone oxidoreductase; and several aerobic/anaerobic enzyme pairs in central carbon metabolism and tetrapyrroles and nucleic acids biosynthesis. Overall, genomic information is consistent with a high tolerance for oxygen that has been reported in the growth of Cfl. aurantiacus. Genes for the chimeric photosystem, photosynthetic electron transport chain, the 3-hydroxypropionate autotrophic carbon fixation cycle, CO2-anaplerotic pathways, glyoxylate cycle, and sulfur reduction pathway are present. The central carbon metabolism and sulfur assimilation pathways in Cfl. aurantiacus are discussed. Some features of the Cfl. aurantiacus genome are compared with those of the Roseiflexus castenholzii genome. Roseiflexus castenholzii is a recently characterized FAP bacterium and phylogenetically closely related to Cfl. aurantiacus. According to previous reports and the genomic information, perspectives of Cfl. aurantiacus in the evolution of photosynthesis are also discussed.ConclusionsThe genomic analyses presented in this report, along with previous physiological, ecological and biochemical studies, indicate that the anoxygenic phototroph Cfl. aurantiacus has many interesting and certain unique features in its metabolic pathways. The complete genome may also shed light on possible evolutionary connections of photosynthesis.

Functional Genomics of Anoxygenic Green Bacteria Chloroflexi Species and Evolution of Photosynthesis

“…The recent genomic report on Cfl. aurantiacus [5], along with previous physiological, ecological and biochemical studies, indicate that the anoxygenic phototroph bacterium Cfl. aurantiacus has many interesting and certain unique features in its metabolic pathways.…”

“…The complete genomic sequence of Cfl. aurantiacus has been recently determined, analyzed and compared to the genomes of other photosynthetic bacteria [5].…”

“…aurantiacus genome contains numerous aerobic/anaerobic gene pairs and oxygenic/anoxygenic metabolic pathways in the Cfl. aurantiacus genome [5], suggesting numerous gene adaptations/replacements in Cfl. aurantiacus to facilitate life under both anaerobic and aerobic growth conditions.…”

“…aurantiacus to facilitate life under both anaerobic and aerobic growth conditions. These include duplicate genes and gene clusters for the alternative complex III (ACIII) [26,27], auracyanin (a type I blue copper protein) [28,29] and NADH:quinone oxidoreductase (complex I); and several aerobic/anaerobic enzyme pairs in central carbon metabolism (pyruvate metabolism and the tricarboxylic acid (TCA) cycle) and tetrapyrroles and nucleic acids biosynthesis [5]. Overall, genomic information is consistent with a high tolerance for oxygen that has been reported in the growth of Cfl.…”

Photosynthesis in Extreme Environments

“…According to 16S rRNA analysis, Chloroflexi species are the earliest branching bacteria capable of photosynthesis, and they have been long regarded as a key organism to resolve the obscurity of the origin and early evolution of photosynthesis. Chloroflexi species contains a chimeric photosystem that comprises some characters of green sulfur bacteria and purple photosynthetic bacteria, and also has some unique electron transport proteins compared to other photosynthetic bacteria (Tang et al, 2011).…”