A molecular phylogenetic survey of polar sea ice microbial communities

The structure of the Antarctic sea ice cover is highly heterogenous, with composition in a given region depending on extremely localised physical processes. Past studies have revealed a wide range of sea ice microbial communities (SIMCO's), associated with a variety of ice types. Many of these assemblages are highly productive. Given the enormous extent of the ice cover these localised but highly productive communities constitute an important component of the regions biological processes. To date, our knowledge of the taxonomical composition of SIMCO's extends from culture based studies. This study employed culture independent molecular techniques to identify biodiversity in a variety of SIMCO's. Clone libraries of 16S rRNA genes were constructed from the total environmental DNA extracted from one Arctic and seven Antarctic sea ice samples using universally-conserved, Archaea-specific and Bacteria-specific 16S rDNA primers. A total of 539 recombinant clones were obtained. Restriction fragment length polymorphism (RFLP) and sequence analysis grouped the clones into 100 distinct phylotypes (a unique clone or group of clones with sequence similarity >0.98) representing sympagic organisms of Bacterial and Eukaryotic origin. Bacterial clones were affiliated with the alpha and gamma Proteobacteria, the Cytophaga-Flavobacterium-Bacteroides Group, the ChlamydialVerricomicrobia and the Gram positive bacteria. One clone was not closely affiliated with any Bacterial Division. Eukaryotic clones were affiliated with a variety of autotrophic and heterotrophic nanoplankton and included a large number of plastid genes. A number of sequences from both groups represented putatively novel organisms. The findings of this examination corroborate data previously collected during culture based studies indicating bacterial biodiversity increases in SIMCO's displaying high levels of primary productivity. Shifts in community composition appear to be associated with alterations in the carbon budget. A comparison of Arctic and Antarctic sea ice communities revealed several common genera occuring at both poles. The information gained from this study provides a focus for a number of important future studies including in situ based analyses of SIMCO composition, cultivation of novel organims identified by sequence anlaysis, and the examination of biogeography of polar sea ice microbial bacteria.