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A Cryptic Sulfur Cycle in Oxygen-Minimum–Zone Waters off the Chilean Coast

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Science  03 Dec 2010:
Vol. 330, Issue 6009, pp. 1375-1378
DOI: 10.1126/science.1196889

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Cryptic Sulfur Cycling

Aerobic bacteria and ocean circulation patterns control the formation and distribution of oxygen-minimum zones at moderate depth in the oceans. These habitats host microorganisms that thrive on other metabolic substrates in the absence of oxygen—most commonly, metabolizing thermodynamically favorable nitrogen compounds like nitrate. Off the coast of Chile, however, Canfield et al. (p. 1375, published online 11 November; see the Perspective by Teske) suggest that bacteria may often reduce sulfate as well. Metagenomic sequencing revealed the presence of both sulfate-reducing and sulfide-oxidizing bacteria. With the coincidence of sulfate and nitrate reduction, the sulfur and nitrogen cycles may be intimately linked; for example, sulfate reduction could provide nitrogen-rich ammonium for bacteria that ultimately transform it into nitrogen gas.

Abstract

Nitrogen cycling is normally thought to dominate the biogeochemistry and microbial ecology of oxygen-minimum zones in marine environments. Through a combination of molecular techniques and process rate measurements, we showed that both sulfate reduction and sulfide oxidation contribute to energy flux and elemental cycling in oxygen-free waters off the coast of northern Chile. These processes may have been overlooked because in nature, the sulfide produced by sulfate reduction immediately oxidizes back to sulfate. This cryptic sulfur cycle is linked to anammox and other nitrogen cycling processes, suggesting that it may influence biogeochemical cycling in the global ocean.

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