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Applied and Environmental Microbiology, September 2008, p. 5802-5808, Vol. 74, No. 18
0099-2240/08/$08.00+0     doi:10.1128/AEM.00852-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Relative Importance of H2 and H2S as Energy Sources for Primary Production in Geothermal Springs{triangledown} ,{dagger}

Seth D'Imperio,1 Corinne R. Lehr,1,{ddagger} Harry Oduro,2 Greg Druschel,2 Michael Kühl,3 and Timothy R. McDermott1*

Thermal Biology Institute and Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana 59717,1 Department of Geology, University of Vermont, Burlington, Vermont 05405,2 Department of Biology, University of Copenhagen, DK-3000 Helsingør, Denmark3

Received 14 April 2008/ Accepted 11 July 2008

Geothermal waters contain numerous potential electron donors capable of supporting chemolithotrophy-based primary production. Thermodynamic predictions of energy yields for specific electron donor and acceptor pairs in such systems are available, although direct assessments of these predictions are rare. This study assessed the relative importance of dissolved H2 and H2S as energy sources for the support of chemolithotrophic metabolism in an acidic geothermal spring in Yellowstone National Park. H2S and H2 concentration gradients were observed in the outflow channel, and vertical H2S and O2 gradients were evident within the microbial mat. H2S levels and microbial consumption rates were approximately three orders of magnitude greater than those of H2. Hydrogenobaculum-like organisms dominated the bacterial component of the microbial community, and isolates representing three distinct 16S rRNA gene phylotypes (phylotype = 100% identity) were isolated and characterized. Within a phylotype, O2 requirements varied, as did energy source utilization: some isolates could grow only with H2S, some only with H2, while others could utilize either as an energy source. These metabolic phenotypes were consistent with in situ geochemical conditions measured using aqueous chemical analysis and in-field measurements made by using gas chromatography and microelectrodes. Pure-culture experiments with an isolate that could utilize H2S and H2 and that represented the dominant phylotype (70% of the PCR clones) showed that H2S and H2 were used simultaneously, without evidence of induction or catabolite repression, and at relative rate differences comparable to those measured in ex situ field assays. Under in situ-relevant concentrations, growth of this isolate with H2S was better than that with H2. The major conclusions drawn from this study are that phylogeny may not necessarily be reliable for predicting physiology and that H2S can dominate over H2 as an energy source in terms of availability, apparent in situ consumption rates, and growth-supporting energy.

* Corresponding author. Mailing address: Thermal Biology Institute and Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717. Phone: (406) 994-2190. Fax: (406) 994-3933. E-mail: timmcder{at}montana.edu

{triangledown} Published ahead of print on 18 July 2008.

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

{ddagger} Present address: Department of Chemistry and Biochemistry, California Polytechnic State University, San Luis Obispo, CA 93407.

Applied and Environmental Microbiology, September 2008, p. 5802-5808, Vol. 74, No. 18
0099-2240/08/$08.00+0     doi:10.1128/AEM.00852-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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  • Clingenpeel, S. R., D'Imperio, S., Oduro, H., Druschel, G. K., McDermott, T. R. (2009). Cloning and In Situ Expression Studies of the Hydrogenobaculum Arsenite Oxidase Genes. Appl. Environ. Microbiol. 75: 3362-3365 [Abstract] [Full Text]  


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