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Archaeal (Per)Chlorate Reduction at High Temperature: An Interplay of Biotic and Abiotic Reactions

Science  05 Apr 2013:
Vol. 340, Issue 6128, pp. 85-87
DOI: 10.1126/science.1233957

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Perchlorate is a ubiquitous chlorine-based compound that forms naturally in the atmosphere. It is only present in large deposits in a few locations, such as the Atacama Desert in Chile, which has been assumed to be because perchlorate-reducing bacteria normally degrade it into chloride and oxygen. Liebensteiner et al. (p. 85; see the Perspective by Nerenberg), however, found that an archeon, Archaeoglobus fulgidus, can also reduce perchlorate. The archaeal perchlorate reduction pathway shares limited similarity with bacterial perchlorate reduction: Instead of producing chloride and oxygen, enzymatically produced chlorite reacts with sulfide to produce oxidized sulfur compounds. Because hyperthermophilic anaerobic archaea similar to A. fulgidus are thought to have been among the first complex organisms to evolve on Earth, they may have started creating oxidized conditions in some habitats before the emergence of oxygen-generating photosynthesis.

Abstract

Perchlorate and chlorate anions [(per)chlorate] exist in the environment from natural and anthropogenic sources, where they can serve as electron acceptors for bacteria. We performed growth experiments combined with genomic and proteomic analyses of the hyperthermophile Archaeoglobus fulgidus that show (per)chlorate reduction also extends into the archaeal domain of life. The (per)chlorate reduction pathway in A. fulgidus relies on molybdo-enzymes that have similarity with bacterial enzymes; however, chlorite is not enzymatically split into chloride and oxygen. Evidence suggests that it is eliminated by an interplay of abiotic and biotic redox reactions involving sulfur compounds. Biological (per)chlorate reduction by ancient archaea at high temperature may have prevented accumulation of perchlorate in early terrestrial environments and consequently given rise to oxidizing conditions on Earth before the rise of oxygenic photosynthesis.

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