Microbial Diversity in Permafrost

Viable bacteria in permafrost were first documented as a part of investigations of mammoths in Siberia (Becker and Volkmann 1961; Cameron and Morelli 1974). High numbers of viable microorganisms (up to 105-107 CFU g-1) were reported by plating, and main efforts were directed to application of molecular tools through sequencing of 16S rDNA (Shi et al. 1997; Zhou et al. 1997). The detected phylo-types formed 11 established lines of descent of bacteria and one entirely new sequence not assigned to any of the known groups. Most of the clones belonged to the alpha (20.9%) and delta (25.6%) subdivisions of the Proteobacteria, with lesser proportions in the beta (9.3%) and gamma (4.7%) subdivisions, groups typically isolated from soil by culture methods. The majority of permafrost-derived clones (77%) had sequences similarities less than 95-80% with those in the database, indicating the predominance of new genera or families.

In the last 5-10 years, the highest number of new microbial species have come from aquatic cold habitats: sea ice, polar lakes and snow crust. Surprisingly, sea ice presented the unique particular case of a high degree of culturability of the natural community (up to 65% from direct microscopic count) (Junge et al. 2002). Culture-independent analysis based on 16S rRNA and conventional isolation revealed rather limited diversity of psychrophilic organisms, all of them belonging to either Proteobacteria or Cytophaga-Flexibacter-Bacteroides (Gosink and Staley 1995; Irgens et al. 1996; Gosink et al. 1998; Junge et al. 1998, 2002; Staley and Gosink 1999). Microbial communities of the continental icy habitats, including Lake Vostok accretion ice (Christner et al. 2001; Brinkmeyer et al. 2003), Tibetan plateau ancient glacier (Christner et al. 2003a, b) and cold deep Atlantic sediments (Xu et al. 2003), seem to be more diverse.

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