• 16S rDNA;
  • Antarctica;
  • oscillatorian;
  • polar cyanobacteria;
  • psychrophile;
  • psychrotolerance

The evolutionary relationships of cultivated psychrophilic and psychrotolerant polar oscillatorians were examined, based on small subunit rDNA sequences. Psychrophilic oscillatorians from the Antarctic were affiliated in one well-supported clade, which also includes two Arctic strains. Two of the Antarctic psychrophiles contain an 11-nucleotide insertion that is identical to, and previously only described in, an Arctic oscillatorian. The psychrotolerant phenotype, conversely, has arisen multiple times in the cyanobacterial lineage, and psychrotolerant strains are sometimes most closely related to organisms of temperate latitudes. These findings support the hypothesis that oscillatorians in both polar regions originated from more temperate species. Furthermore, morphological designations of these filamentous cyanobacteria often do not have phylogenetic significance.