Morphology and phylogenetic relationships of some psychrophilic polar diatoms (Bacilariophyta)

Abstract

Nine psychrophilic polar diatom species within six genera (Chaetoceros, Fragilaria, Navicula, Nitzschia, Porosira, and Stellarima) were found near King Sejong Station, Maxwell Bay, King George Island, Antarctica and near Dasan Station, Ny-？lesund, Svalbard, in the Arctic, in November 1998 and January 2005, respectively. These psychrophilic diatoms all thrived at approximately 2℃ under 25 ？mol photons m-2 s-1. We attempted to access the diversity of psychrophilic polar diatoms cultivated in the culture room of the Korea Polar Research Institute (KOPRI) Culture Collections for Polar Microorganisms (KCCPM) and to establish the phylogenetic relationships among diverse diatoms based on morphological and molecular data. We determined 14 nuclear SSU rDNA and 18 plastid rbcL sequences and the data were deposited in GenBank. Our SSU tree recovered very similar divergence patterns to that of a previous SSU tree. In the SSU tree, the species were generally placed in the deep branches of each clade. Although the phylogeny inferred from rbcL data was somewhat different from that from SSU data at higher taxonomic levels within the diatoms, rbcL data were more useful than SSU data for addressing phylogenetic affinities among closely related taxa.