Phylogenetic diversity of picocyanobacteria in Arctic and Antarctic ecosystems

Abstract

Oxyphotobacteria ascribed to the genera Synechococcus and Synechocystis are widely distributed in Arctic and Antarctic lakes, yet they are poorly represented in the marine polar environment. Arctic lakes contain phycoerythrin-rich as well as phycocyanin-rich picoplankton, implying a level of genetic diversity within this group that is poorly resolved by classic taxonomic criteria. Our culture studies of isolates from ponds on Bylot Island in the Canadian Arctic (lat. 74 o N, long. 135 o W) show that strains with similar pigment and morphological characteristics differ genetically in terms of their growth versus irradiance parameters. Application of 16S rDNA analysis to these picocyanobacterial isolates shows that they are most closely related to Microcystis elabens (98-99% similarity), and more distantly related to Synechococcus sp. PCC6301 (95%), Prochlorococcus marinus (93%) and Synechocystis sp. PCC6803 (90%). Picocyanobacteria have been observed among the water column dominants in a variety of Antarctic lakes, for example in the deep Chl a maximum of Lake Vanda (lat. 78 o S, long. 105 o E). In the saline lakes of the Vestfold Hills region (lat. 68 o S, long. 100 o E) their concentrations attain up to 8 x 10 6 cells/ml. Analysis of the 16S rDNA of phycoerythrin-rich isolates from lakes in this region show that they form a distinct cluster, most closely related (97% similar) to P. marinus.