16S-LIKE RDNA SEQUENCE AND PHYLOGENETIC POSITION OF THE DIPLOMONAD SPIRONUCLEUS-MURIS (LAVIER 1936)

The sequence of the small subunit (SSU) rDNA gene of the facultative p athogenic flagellate Spironucleus muris has been determined. This flag ellate belongs to the class Diplomonadida. We will set out its phyloge netic position within the eukaryotic tree according to its morphologic al characteristics. Cells of Spironucleus muris were enriched from the digestive tract of immunodeficient mice and the DNA was extracted. Af ter sequencing the SSU rDNA insert (1206 bp), we carried out a compara tive sequence analysis with accessible SSU rRNA sequences from related eukaryotes. Escherichia coli and Methanospirillum hungatei were used as outgroups. Spironucleus muris shows strongest structural similarity (73.2%) to the parasitic flagellate Hexamita inflata (class Diplomona dida), which originated very early in the enkaryotic tree.