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

Publication Type:
Journal Article
Citation:
ISME Journal, 2012, 6 (10), pp. 1869 - 1882
Issue Date:
2012-10-01
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An uncultured member of the phylum Chlorobi, provisionally named Candidatus Thermochlorobacter aerophilum, occurs in the microbial mats of alkaline siliceous hot springs at the Yellowstone National Park. Ca. T. aerophilum was investigated through metagenomic and metatranscriptomic approaches. Ca. T. aerophilum 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. Ca. T. aerophilum is proposed to be an aerobic photoheterotroph that cannot oxidize sulfur compounds, cannot fix N 2, and does not fix CO 2 autotrophically. Metagenomic analyses suggest that Ca. T. aerophilum depends on other mat organisms for fixed carbon and nitrogen, several amino acids, and other important nutrients. The failure to detect bchU suggests that Ca. T. aerophilum 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 Ca. T. aerophilum 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. © 2012 International Society for Microbial Ecology. All rights reserved.
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