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Applied and Environmental Microbiology, April 2009, p. 1801-1810, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.01811-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Diversity and Stratification of Archaea in a Hypersaline Microbial Mat ^,

Charles E. Robertson,¹ John R. Spear,² J. Kirk Harris,³ and Norman R. Pace^1*

Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347,¹ Division of Environmental Science and Engineering, Colorado School of Mines, Golden, Colorado 80401,² Department of Pediatrics, University of Colorado Denver, Aurora, Colorado 80045³

Received 5 August 2008/ Accepted 16 December 2008

The Guerrero Negro (GN) hypersaline microbial mats have become one focus for biogeochemical studies of stratified ecosystems. The GN mats are found beneath several of a series of ponds of increasing salinity that make up a solar saltern fed from Pacific Ocean water pumped from the Laguna Ojo de Liebre near GN, Baja California Sur, Mexico. Molecular surveys of the laminated photosynthetic microbial mat below the fourth pond in the series identified an enormous diversity of bacteria in the mat, but archaea have received little attention. To determine the bulk contribution of archaeal phylotypes to the pond 4 study site, we determined the phylogenetic distribution of archaeal rRNA gene sequences in PCR libraries based on nominally universal primers. The ratios of bacterial/archaeal/eukaryotic rRNA genes, 90%/9%/1%, suggest that the archaeal contribution to the metabolic activities of the mat may be significant. To explore the distribution of archaea in the mat, sequences derived using archaeon-specific PCR primers were surveyed in 10 strata of the 6-cm-thick mat. The diversity of archaea overall was substantial albeit less than the diversity observed previously for bacteria. Archaeal diversity, mainly euryarchaeotes, was highest in the uppermost 2 to 3 mm of the mat and decreased rapidly with depth, where crenarchaeotes dominated. Only 3% of the sequences were specifically related to known organisms including methanogens. While some mat archaeal clades corresponded with known chemical gradients, others did not, which is likely explained by heretofore-unrecognized gradients. Some clades did not segregate by depth in the mat, indicating broad metabolic repertoires, undersampling, or both.

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* Corresponding author. Mailing address: Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347. Phone: (303) 735-1864. Fax: (303) 492-7744. E-mail: Norman.Pace{at}colorado.edu

Published ahead of print on 29 December 2008.

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

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Applied and Environmental Microbiology, April 2009, p. 1801-1810, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.01811-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.