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

Abstract

Members of the genus Protostelium (including P. mycophaga, P. nocturnum, and P. okumukumu) are protosteloid amoebae commonly found in terrestrial habitats on dead plant matter. They, along with the closely allied nominal genus Planoprotostelium, containing the single species Pl. aurantium, 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 Pl. aurantium which looks similar to P. mycophaga 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 Protostelium and Planoprotostelium and found that (1) the nonflagellated P. nocturnum and P. okumukumu branch basally in the genus Protostelium, (2) the flagellate, Pl. aurantium falls within the genus Protostelium in a monophyletic clade with the nominal variety, P. mycophaga var. crassipes, (3) the cultures initially identified as Protostelium mycophaga can be divided into at least three morphologically recognizable taxa, P. aurantium n. comb., P. apiculatum n. sp., and P. m. rodmani n. subsp., as well as a paraphyletic assemblage that includes the remainder of the P. mycophaga 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.

Multiple Roots of Fruiting Body Formation in Amoebozoa

“…Phylogenic analysis based on its SSU rRNA ( fig. 2 A ) as well as diagnostic morphological traits identified the isolate as a strain of Protostelium aurantium as recently described by Shadwick et al. (2017) .…”

The fungivorous amoeba Protostelium aurantium targets redox homeostasis and cell wall integrity during intracellular killing of Candida parapsilosis

“…Amoebae are predominant environmental micro-predators, but only a few of them have been described to actively feed on fungi (Chakraborty et al, 1983;Old, 1977;Old & Darbyshire, 1978). Such a fungivorous lifestyle has been described for Protostelium mycophagum, the type species for the polyphyletic group of protosteloid amoebae that form microscopic, stalked fruiting bodies from single cells and are found on nearly all continents (Kang et al, 2017;Shadwick et al, 2018;Spiegel et al, 2017). We have recently isolated and characterized a strain of P. aurantium (formerly known as Planoprotostelium aurantium), which was found to selectively recognise, kill and feed on a wide range of ascomycete and basidiomycete yeasts, including major human pathogens of the Candida clade (Radosa et al, 2019).…”

The different morphologies of yeast and filamentous fungi trigger distinct killing and feeding mechanisms in a fungivorous amoeba

“…In general, protosteloid amoebae are widely distributed across the phylogenetic tree of the Amoebozoa (Shadwick et al, ; Kang et al, ; Spiegel et al, ). Protostelium aurantium (formerly known as Planoprotostelium aurantium ) is part of the P. mycophagum (‘ fungus eating ’) clade whose members are true cosmopolitans and have been recovered from all continents except Antarctica (Aguilar et al, ; Ndiritu et al, ; Hillmann et al, ; Shadwick et al, ). Their ecological impact has remained poorly defined, but a systematic study found P. mycophaga to be by far the most abundant protosteloid amoebae in aerial or ground litter microhabitats in New Zealand (Zahn et al, ).…”