Variation in the SSUrDNA of the Genus <italic>Protostelium</italic> Leads to a New Phylogenetic Understanding of the Genus and of the Species Concept for <italic>Protostelium mycophaga</italic> (Protosteliida, Amoebozoa).

Abstract: Members of the genus <italic>Protostelium</italic> (including <italic>P. mycophaga</italic>,<italic> P. nocturnum</italic>, and <italic>P. okumukumu</italic>) are protosteloid amoebae commonly found in terrestrial habitats on dead plant matter. They, along with the closely allied nominal genus <italic>Planoprotostelium</italic>, containing the single species <italic>Pl. aurantium</italic>, all have an amoeboid trophic stage with acutely pointed subpseudopodia and orange lipid droplets in the granuloplasm. These amoebae form stalked fruiting bodies topped with a single, usually deciduous spore. The species are identified based on their fruiting body morphologies except for <italic>Pl. aurantium</italic> which looks similar to <italic>P. mycophaga</italic> in fruiting morphology, but has amoebae that can make flagella in liquid medium. We built phylogenetic trees using nuclear small subunit ribosomal DNA sequences of 35 isolates from the genera <italic>Protostelium</italic> and <italic>Planoprotostelium</italic> and found that (1) the nonflagellated <italic>P. nocturnum</italic> and <italic>P. okumukumu</italic> branch basally in the genus <italic>Protostelium</italic>, (2) the flagellate, <italic>Pl. aurantium</italic> falls within the genus <italic>Protostelium</italic> in a monophyletic clade with the nominal variety, <italic>P. mycophaga</italic> var. <italic>crassipes</italic>, (3) the cultures initially identified as <italic>Protostelium mycophaga</italic> can be divided into at least three morphologically recognizable taxa, <italic>P. aurantium</italic> n. comb., <italic>P. apiculatum</italic> n. sp., and <italic>P. m. rodmani</italic> n. subsp., as well as a paraphyletic assemblage that includes the remainder of the <italic>P. mycophaga</italic> morphotype. These findings have implications for understanding the ecology, evolution, and diversity of these amoeboid organisms and for using these amoebae as models for other amoeboid groups. [ABSTRACT FROM AUTHOR]