AEM Accepts, published online ahead of print on 13 June 2008

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Appl. Environ. Microbiol. doi:10.1128/AEM.00455-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Microbial diversity of a meromictic soda lake in Washington, USA: spatial and temporal patterns

Pedro A. Dimitriu^*, Holly C. Pinkart, Brent M. Peyton, and Melanie R. Mormile

Biological Sciences Department, University of Missouri-Rolla, Rolla, MO, 65409-1120, USA; Department of Biological Sciences, Central Washington University, Ellensburg, WA, 98926, USA; Chemical and Biological Engineering, Montana State University, Bozeman, MT 59717-3920, USA

^* To whom correspondence should be addressed. Email: dimitriu{at}interchange.ubc.ca.

The microbial community diversity and composition of meromictic Soap Lake were studied using culture-dependent and culture-independent approaches. The water column and sediments were sampled monthly for a year. Denaturing gradient gel electrophoresis (DGGE) of bacterial and archaeal 16S rRNA genes showed an increase in diversity with depth for both groups. Late-summer samples harbored the highest prokaryotic diversity, and bacteria experienced less seasonal variability than the archaea. Most-probable number (MPN) assays targeting anaerobic microbial guilds were established to compare summer (S) and fall (F) samples. In both seasons, the anoxic samples appeared to be dominated by lactate-oxidizing sulfate-reducing prokaryotes. Lactate- and acetate-oxidizing iron-reducing bacteria, as well as fermentative microorganisms, were also found at high numbers, whereas numbers of methanogens were low or undetectable. The bacterial community composition of S and F samples was also assessed by constructing 16S rRNA gene clone libraries. A total of 508 sequences represented an estimated >1,100 unique OTUs, most of them from the monimolimnion, with S samples being more diverse than F samples (Chao1 = 530 and 295, respectively). For both seasons, mixolimnion sequences were dominated by -Proteobacteria, and the chemocline and the monimolimnion libraries were dominated by low G+C group members, followed by the Cytophaga-Flexibacter-Bacteroides (CFB) group; the mixolimnion sediments were represented by sequences related to uncultured groups of Chloroflexi and CFB. Community overlap and phylogenetic analyses, however, not only demonstrated a high degree of spatial turnover, but also suggested a degree of temporal variability contributed by differences in the communities' memberships and structures.

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