AME 66:283-293 (2012)  -  DOI:

Denitrification by sulfur-oxidizing bacteria in a eutrophic lake

Amy J. Burgin1,2,3,*, Stephen K. Hamilton1,2, Stuart E. Jones1,4, Jay T. Lennon1,5

1W. K. Kellogg Biological Station, 2Department of Zoology and 5Department of Microbiology and Molecular Genetics, Michigan State University, 3700 East Gull Lake Dr., Hickory Corners, Michigan 49060, USA
3Present address: School of Natural Resources, University of Nebraska-Lincoln, 3310 Holdredge St., 412 Hardin Hall, Lincoln, Nebraska 68583-0974, USA 4Present address: Department of Biological Sciences, University of Notre Dame, 264 Galvin Hall, Notre Dame, Indiana 46556, USA 6Present address: Department of Biology, Indiana University, 1001 E. 3rd St., Bloomington, Indiana 47405–3700, USA

ABSTRACT: Understanding the mechanistic controls of microbial denitrification is of central importance to both environmental microbiology and ecosystem ecology. Loss of nitrate (NO3) is often attributed to carbon-driven (heterotrophic) denitrification. However, denitrification can also be coupled to sulfur (S) oxidation by chemolithoautotrophic bacteria. In the present study, we used an in situ stable isotope (15NO3) tracer addition in combination with molecular approaches to understand the contribution of sulfur-oxidizing bacteria to the reduction of NO3 in a eutrophic lake. Samples were incubated across a total dissolved sulfide (H2S) gradient (2 to 95 ┬ÁM) between the lower epilimnion and the upper hypolimnion. Denitrification rates were low at the top of the chemocline (4.5 m) but increased in the deeper waters (5.0 and 5.5 m), where H2S was abundant. Concomitant with increased denitrification at depths with high sulfide was the production of sulfate (SO42−), suggesting that the added NO3 was used to oxidize H2S to SO42−. Alternative nitrate removal pathways, including dissimilatory nitrate reduction to ammonium (DNRA) and anaerobic ammonium oxidation (anammox), did not systematically change with depth and accounted for 1 to 15% of the overall nitrate loss. Quantitative PCR revealed that bacteria of the Sulfurimonas genus that are known denitrifiers increased in abundance in response to NO3 addition in the treatments with higher H2S. Stoichiometric estimates suggest that H2S oxidation accounted for more than half of the denitrification at the depth with the highest sulfide concentration. The present study provides evidence that microbial coupling of S and nitrogen (N) cycling is likely to be important in eutrophic freshwater ecosystems.

KEY WORDS: Denitrification · Nitrate reduction · Sulfur oxidation · Sulfur-driven denitrification · Sulfurimonas denitrificans · Sulfide · Wintergreen Lake

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Cite this article as: Burgin AJ, Hamilton SK, Jones SE, Lennon JT (2012) Denitrification by sulfur-oxidizing bacteria in a eutrophic lake. Aquat Microb Ecol 66:283-293.

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