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Applied and Environmental Microbiology, May 2006, p. 3685-3695, Vol. 72, No. 5
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.5.3685-3695.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Unexpected Diversity and Complexity of the Guerrero Negro Hypersaline Microbial Mat

Ruth E. Ley,1,2,{dagger} J. Kirk Harris,1,2 Joshua Wilcox,1,2 John R. Spear,1,2,{ddagger} Scott R. Miller,3 Brad M. Bebout,4 Julia A. Maresca,5 Donald A. Bryant,5 Mitchell L. Sogin,6 and Norman R. Pace1,2*

Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309,1 Center for Astrobiology, University of Colorado at Boulder, Boulder, Colorado 80309,2 Division of Biological Sciences, The University of Montana, Missoula, Montana 59812,3 Exobiology Branch, NASA Ames Research Center, Moffett Field, California 94035,4 Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802,5 The Marine Biological Laboratory, Woods Hole, Massachusetts 025436

Received 14 December 2005/ Accepted 26 February 2006

We applied nucleic acid-based molecular methods, combined with estimates of biomass (ATP), pigments, and microelectrode measurements of chemical gradients, to map microbial diversity vertically on a millimeter scale in a hypersaline microbial mat from Guerrero Negro, Baja California Sur, Mexico. To identify the constituents of the mat, small-subunit rRNA genes were amplified by PCR from community genomic DNA extracted from layers, cloned, and sequenced. Bacteria dominated the mat and displayed unexpected and unprecedented diversity. The majority (1,336) of the 1,586 bacterial 16S rRNA sequences generated were unique, representing 752 species (≥97% rRNA sequence identity) in 42 of the main bacterial phyla, including 15 novel candidate phyla. The diversity of the mat samples differentiated according to the chemical milieu defined by concentrations of O2 and H2S. Bacteria of the phylum Chloroflexi formed the majority of the biomass by percentage of bulk rRNA and of clones in rRNA gene libraries. This result contradicts the general belief that cyanobacteria dominate these communities. Although cyanobacteria constituted a large fraction of the biomass in the upper few millimeters (>80% of the total rRNA and photosynthetic pigments), Chloroflexi sequences were conspicuous throughout the mat. Filamentous Chloroflexi bacteria were identified by fluorescence in situ hybridization within the polysaccharide sheaths of the prominent cyanobacterium Microcoleus chthonoplastes, in addition to free living in the mat. The biological complexity of the mat far exceeds that observed in other polysaccharide-rich microbial ecosystems, such as the human and mouse distal guts, and suggests that positive feedbacks exist between chemical complexity and biological diversity.

* 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: nrpace{at}colorado.edu.

{dagger} Present address: Center for Genome Sciences, Washington University, St. Louis, MO 63108.

{ddagger} Present address: Division of Environmental Science and Engineering, Colorado School of Mines, Golden, CO 80401.

Applied and Environmental Microbiology, May 2006, p. 3685-3695, Vol. 72, No. 5
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.5.3685-3695.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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