Abstract
Protothecosis is an infectious disease caused by organisms currently classified within the green algal genus Prototheca. The disease can manifest as cutaneous lesions, olecranon bursitis or disseminated or systemic infections in both immunocompetent and immunosuppressed patients. Concerning diagnostics, taxonomic validity is important. Prototheca, closely related to the Chlorella species complex, is known to be polyphyletic, branching with Auxenochlorella and Helicosporidium. The phylogeny of Prototheca was discussed and revisited several times in the last decade; new species have been described. Phylogenetic analyses were performed using ribosomal DNA (rDNA) and partial mitochondrial cytochrome b (cytb) sequence data. In this work we use Internal Transcribed Spacer 2 (ITS2) as well as 18S rDNA data. However, for the first time, we reconstruct phylogenetic relationships of Prototheca using primary sequence and RNA secondary structure information simultaneously, a concept shown to increase robustness and accuracy of phylogenetic tree estimation. Using encoded sequence-structure data, Neighbor-Joining, Maximum-Parsimony and Maximum-Likelihood methods yielded well-supported trees in agreement with other trees calculated on rDNA; but differ in several aspects from trees using cytb as a phylogenetic marker. ITS2 secondary structures of Prototheca sequences are in agreement with the well-known common core structure of eukaryotes but show unusual differences in their helix lengths. An elongation of the fourth helix of some species seems to have occurred independently in the course of evolution.
Highlights
According to Algaebase (Guiry and Guiry, 2021), organisms, colorless and apochlorotic, without chloroplasts and pyrenoids, currently classified as Prototheca W.Krüger, 1894 (Chlorophyta, Trebouxiophyceae) are widely distributed from temperate to tropical conditions in both fresh and marine waters
5.8S 28S stem d P. ulmea b P. cutis e P. xanthoriae c P. stagnorum f P. zopfii on ribosomal DNA (rDNA) sequences proposed in literature but show several topological differences to trees calculated on cytb sequences
Prototheca wickerhamii, the main causative for human protothecosis, could not be included in analysis based on Internal Transcribed Spacer 2 (ITS2) data since its ITS2 sequences were exceptionally long and could not be aligned with other Prototheca sequences
Summary
According to Algaebase (Guiry and Guiry, 2021), organisms, colorless and apochlorotic, without chloroplasts and pyrenoids, currently classified as Prototheca W.Krüger, 1894 (Chlorophyta, Trebouxiophyceae) are widely distributed from temperate to tropical conditions in both fresh and marine waters. Prototheca and Chlorella are the only known algal genera including disease-causing organisms in humans (Jagielski et al 2019). Prototheca is associated with conditions termed protothecosis (Guiry and Guiry, 2021). Concerning diagnostics, taxonomic validity is important – in particular concerning the pathology associated taxa P. wickerhamii K.Tubaki & M.Soneda, 1959 and P. zopfii W.Krüger, 1894 (type species). Several species of Prototheca are rare opportunistic pathogens (Huerre et al 1993) in humans (Lass-Flörl et al 2007), other mammals (e.g. Möller et al 2007; Marques et al 2008) and fish (Jagielski et al 2017). Protothecosis is an infectious disease, which often spreads through contact with contaminated water (Jagielski and Lagneau, 2007). The disease manifests in three clinical forms: cutaneous lesions, olecranon bursitis and disseminated or systemic infections
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