Hyperamoeba isolated from human feces: Description and phylogenetic affinity

The morphology and phylogenetic affinity of Hyperamoeba isolated from human feces is described. During its life cycle, it switches reversibly from flagellate to aflagellated amoebae and is capable of forming cysts. It grows aerobically. Under anaerobic conditions it persists but does not replicate. The amoeboflagellate has a single nucleus with a distinct nucleolus. Its mitochondria possess tubular cristae and a central electron dense body, similar to that of plasmodial slime molds. A single contractile vacuole is evident. The flagellate has one detectable anterior flagellum but two basal bodies are visible at the ultrastructure level. The flagellar apparatus is very similar to that found in some Eumycetozoa, especially the myxogastrids. The uninucleate cyst has a bi-layered endocyst and a membranous, irregular shaped, faintly laminated ectocyst that harbors bacterial inclusions. Phylogenetic reconstructions based on nuclear small subunit ribosomal gene sequence comparisons show that Hyperamoeba is closely related to the plasmodial slime mold Physarum polycephalum. These protists share a most recent common ancestry that excludes all other taxa in the database. This phylogenetic relationship is supported by detailed similarities in both mitochondrial and flagellar apparatus ultrastructure.