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Applied and Environmental Microbiology, September 2003, p. 5609-5621, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5609-5621.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Bacterial Diversity and Sulfur Cycling in a Mesophilic Sulfide-Rich Spring

Mostafa S. Elshahed,1 John M. Senko,1 Fares Z. Najar,2 Stephen M. Kenton,2 Bruce A. Roe,2 Thomas A. Dewers,3 John R. Spear,4 and Lee R. Krumholz1*

Department of Botany and Microbiology and Institute for Energy and the Environment,1 Department of Chemistry and Biochemistry,2 Department of Geology and Geophysics, University of Oklahoma, Norman, Oklahoma,3 Department of Biology, University of Colorado, Boulder, Colorado4

Received 5 February 2003/ Accepted 25 June 2003

An artesian sulfide- and sulfur-rich spring in southwestern Oklahoma is shown to sustain an extremely rich and diverse microbial community. Laboratory incubations and autoradiography studies indicated that active sulfur cycling is occurring in the abundant microbial mats at Zodletone spring. Anoxygenic phototrophic bacteria oxidize sulfide to sulfate, which is reduced by sulfate-reducing bacterial populations. The microbial community at Zodletone spring was analyzed by cloning and sequencing 16S rRNA genes. A large fraction (83%) of the microbial mat clones belong to sulfur- and sulfate-reducing lineages within {delta}-Proteobacteria, purple sulfur {gamma}-Proteobacteria, {varepsilon}-Proteobacteria, Chloroflexi, and filamentous Cyanobacteria of the order Oscillatoria as well as a novel group within {gamma}-Proteobacteria. The 16S clone library constructed from hydrocarbon-exposed sediments at the source of the spring had a higher diversity than the mat clone library (Shannon-Weiner index of 3.84 compared to 2.95 for the mat), with a higher percentage of clones belonging to nonphototrophic lineages (e.g., Cytophaga, Spirochaetes, Planctomycetes, Firmicutes, and Verrucomicrobiae). Many of these clones were closely related to clones retrieved from hydrocarbon-contaminated environments and anaerobic hydrocarbon-degrading enrichments. In addition, 18 of the source clones did not cluster with any of the previously described microbial divisions. These 18 clones, together with previously published or database-deposited related sequences retrieved from a wide variety of environments, could be clustered into at least four novel candidate divisions. The sulfate-reducing community at Zodletone spring was characterized by cloning and sequencing a 1.9-kb fragment of the dissimilatory sulfite reductase (DSR) gene. DSR clones belonged to the Desulfococcus-Desulfosarcina-Desulfonema group, Desulfobacter group, and Desulfovibrio group as well as to a deeply branched group in the DSR tree with no representatives from cultures. Overall, this work expands the division-level diversity of the bacterial domain and highlights the complexity of microbial communities involved in sulfur cycling in mesophilic microbial mats.

* Corresponding author. Mailing address: University of Oklahoma, Department of Botany and Microbiology, 770 Van Vleet Oval, Norman, OK 73071. Phone: (405) 325-4321. Fax: (405) 325-7619. E-mail: Krumholz{at}ou.edu.

Applied and Environmental Microbiology, September 2003, p. 5609-5621, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5609-5621.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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