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© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in eLife 6 (2017): e18990, doi:10.7554/eLife.18990., Anaerobic thermophiles inhabit relic environments that resemble the early Earth. However, the lineage of these modern organisms co-evolved with our planet. Hence, these organisms carry both ancestral and acquired genes and serve as models to reconstruct early metabolism. Based on comparative genomic and proteomic analyses, we identified two distinct groups of genes in Thermovibrio ammonificans: the first codes for enzymes that do not require oxygen and use substrates of geothermal origin; the second appears to be a more recent acquisition, and may reflect adaptations to cope with the rise of oxygen on Earth. We propose that the ancestor of the Aquificae was originally a hydrogen oxidizing, sulfur reducing bacterium that used a hybrid pathway for CO2 fixation. With the gradual rise of oxygen in the atmosphere, more efficient terminal electron acceptors became available and this lineage acquired genes that increased its metabolic flexibility while retaining ancestral metabolic traits., National Science Foundation (MCB 04-56676), (OCE 03-27353), (MCB 08-43678), (OCE 09-37371), (OCE 11-24141), (MCB 15-17567), (OCE-1136727); National Aeronautics and Space Administration (NNX15AM18G)

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in eLife 6 (2017): e18990, doi:10.7554/eLife.18990., Anaerobic thermophiles inhabit relic environments that resemble the early Earth. However, the lineage of these modern organisms co-evolved with our planet. Hence, these organisms carry both ancestral and acquired genes and serve as models to reconstruct early metabolism. Based on comparative genomic and proteomic analyses, we identified two distinct groups of genes in Thermovibrio ammonificans: the first codes for enzymes that do not require oxygen and use substrates of geothermal origin; the second appears to be a more recent acquisition, and may reflect adaptations to cope with the rise of oxygen on Earth. We propose that the ancestor of the Aquificae was originally a hydrogen oxidizing, sulfur reducing bacterium that used a hybrid pathway for CO2 fixation. With the gradual rise of oxygen in the atmosphere, more efficient terminal electron acceptors became available and this lineage acquired genes that increased its metabolic flexibility while retaining ancestral metabolic traits., National Science Foundation (MCB 04-56676), (OCE 03-27353), (MCB 08-43678), (OCE 09-37371), (OCE 11-24141), (MCB 15-17567), (OCE-1136727); National Aeronautics and Space Administration (NNX15AM18G)