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 pathogenic flagellate Spironucleus muris has been determined. This flagellate belongs to the class Diplomonadida. We will set out its phylogenetic position within the eukaryotic tree according to its morphological characteristics. Cells of Spironucleus muris were enriched from the digestive tract of immunodeficient mice and the DNA was extracted. After sequencing the SSU rDNA insert (1206 bp), we carried out a comparative 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 Diplomonadida), which originated very early in the enkaryotic tree.