Phylogenetic position of Psalteriomonas lanterna deduced from the SSU rDNA sequence

The small subunit ribosomal DNA sequence (SSU rDNA) of the microaerophilic free-living amoeboflagellate Psalteriomonas lanterna has been sequenced and analyzed. The gene is 1,945 bp long and has a G + C content of 33.4%. Based upon ultrastructural studies, P. lanterna has been placed in the class Lyromonadea within the phylum Percolozoa Cavalier-Smith, 1991. However, based upon cytological characteristics, this microaerophilic free-living amoeboflagellate appears to be very primitive. It shares certain characteristics in common with some archezoans, i.e. it lacks mitochondria and dictyosomes but contains hydrogenosomes. Despite sharing these characteristics with the amitochondriate taxa, P. lanterna is not related to any of these taxa but instead to the Vahlkampfiidae. Therefore, we used primary sequence data and the secondary structure of the SSU rDNA gene to determine the placement P. lanterna in the phylogenetic tree. Our analyses showed that P. lanterna groups as a sister taxon to the Vahlkampfiidae but probably diverged from them quite early.