Diversity of free-living prokaryotes from a deep-sea site at the AntarcticPolar Front

To contribute to the understanding or deep-sea planktonic communities, we e xplored the prokaryotic diversity. of a 3000 m deep site at the Antarctic P olar Front using molecular methods. Bacterial 16S rDNA-amplified sequences corresponded to the as yet uncultivated groups SAR11, within the alpha -Pro teobacteria, and SAR324. within the delta -Proteobacteria, as well as to th e gamma -Proteobacteria, Cytophagales. Planctomyces, Gram-positives, and th e group of environmental sequences SAR406. Among them, gamma -proteobacteri al sequences were the most abundant and diverse. Within Archaea, and using six different primer sets for 16S rDNA amplification, only euryarchaeotal s equences were retrieved. Most of them clustered with the Thermoplasma-relat ed marine groups II and III, but some corresponded to a recently described group of marine sequences emerging at the base of haloarchaea. Our data sug gest that gamma -Proteobacteria and Euryarchaeota may be dominant elements in terms of genetic diversity of the two prokaryotic domains in this deep-s ea pelagic area. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.