Candidatus Thermochlorobacter aerophilum: an aerobic chlorophotoheterotrophic member of the phylum Chlorobi defined by metagenomics and metatranscriptomics

Nature Publishing Group
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Journal Article
ISME Journal, 2012, 6 pp. 1869 - 1882
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An uncultured member of the phylum Chlorobi, provisionally named âCandidatus Thermochlorobacter aerophilumâ, occurs in the microbial mats of alkaline siliceous hot springs at the Yellowstone National Park. âCa. T. aerophilumâ was investigated through metagenomic and metatranscriptomic approaches. âCa. T. aerophilumâ is a member of a novel, family-level lineage of Chlorobi, a chlorophototroph that synthesizes type-1 reaction centers and chlorosomes similar to cultivated relatives among the green sulfur bacteria, but is otherwise very different physiologically. âCa. T. aerophilumâ is proposed to be an aerobic photoheterotroph that cannot oxidize sulfur compounds, cannot fix N2, and does not fix CO2 autotrophically. Metagenomic analyses suggest that âCa. T. aerophilumâ depends on other mat organisms for fixed carbon and nitrogen, several amino acids, and other important nutrients. The failure to detect bchU suggests that âCa. T. aerophilumâ synthesizes bacteriochlorophyll (BChl) d, and thus it occupies a different ecological niche than other chlorosome-containing chlorophototrophs in the mat. Transcription profiling throughout a diel cycle revealed distinctive gene expression patterns. Although âCa. T. aerophilumâ probably photoassimilates organic carbon sources and synthesizes most of its cell materials during the day, it mainly transcribes genes for BChl synthesis during late afternoon and early morning, and it synthesizes and assembles its photosynthetic apparatus during the night.
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