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Applied and Environmental Microbiology, July 2009, p. 4289-4296, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02751-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

CO2 Uptake and Fixation by a Thermoacidophilic Microbial Community Attached to Precipitated Sulfur in a Geothermal Spring{triangledown} ,{dagger}

Eric S. Boyd,1,{ddagger} William D. Leavitt,2,§ and Gill G. Geesey1*

Department of Microbiology and Thermal Biology Institute, Montana State University, Bozeman, Montana 59717,1 School of Natural Science, Hampshire College, Amherst, Massachusetts 010022

Received 2 December 2008/ Accepted 30 April 2009

Carbon fixation at temperatures above 73°C, the upper limit for photosynthesis, is carried out by chemosynthetic thermophiles. Yellowstone National Park (YNP), Wyoming possesses many thermal features that, while too hot for photosynthesis, presumably support chemosynthetic-based carbon fixation. To our knowledge, in situ rates of chemosynthetic reactions at these high temperatures in YNP or other high-temperature terrestrial geothermal springs have not yet been reported. A microbial community attached to precipitated elemental sulfur (So floc) at the source of Dragon Spring (73°C, pH 3.1) in Norris Geyser Basin, YNP, exhibited a maximum rate of CO2 uptake of 21.3 ± 11.9 µg of C 107 cells–1 h–1. When extrapolated over the estimated total quantity of So floc at the spring's source, the So floc-associated microbial community accounted for the uptake of 121 mg of C h–1 at this site. On a per-cell basis, the rate was higher than that calculated for a photosynthetic mat microbial community dominated by Synechococcus spp. in alkaline springs at comparable temperatures. A portion of the carbon taken up as CO2 by the So floc-associated biomass was recovered in the cellular nucleic acid pool, demonstrating that uptake was coupled to fixation. The most abundant sequences in a 16S rRNA clone library of the So floc-associated community were related to chemolithoautotrophic Hydrogenobaculum strains previously isolated from springs in the Norris Geyser Basin. These microorganisms likely contributed to the uptake and fixation of CO2 in this geothermal habitat.

* Corresponding author. Mailing address: Department of Microbiology and Thermal Biology Institute, Montana State University, P.O. Box 173520, Bozeman, MT 59717. Phone: (406) 994-3820. Fax: (406) 994-4926. E-mail: gill_g{at}erc.montana.edu

{triangledown} Published ahead of print on 8 May 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

{ddagger} Present address: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138.

§ Present address: Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717.

Applied and Environmental Microbiology, July 2009, p. 4289-4296, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.02751-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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