Molecular phylogeny and taxonomy of Lagenidium-like oomycetes pathogenic to mammals
Citation
Spies CF, Grooters AM, Lévesque CA, Rintoul TL, Redhead SA, Glockling SL, Chen CY, de Cock AW. 2016. Molecular phylogeny and taxonomy of Lagenidium-like oomycetes pathogenic to mammals
Plain language summary
Serious infections of cats, dogs and humans linked to a group of aquatic fungi that were not known to infect mammals previously have been increasingly detected. The pathogens consist of a group of species with zoospores (swimming spores) classified as Oomycetes (fungus-like organisms not considered to be true Fungi) and in a genus called Lagenidium. Using DNA sequence information combined from 6 gene regions and further correlated with morphological characters in culture, which strengthen the reliability of the analyses these fungus-like species, were shown to belong to 3 species: 2 in Lagenidium and 1 in a distantly related genus, Paralagenidium. The mammalian parasitic Lagenidium were related to 2 other genera, Myzocytiopsis and Salilagenidium, each of which is known to be parasitic on other groups of animals such as insects, nematodes or crustaceans. It is suggested that the potential of infection of mammals by species thought to only infect animals in other phyla should be investigated more thoroughly. One investigated species was excluded from Lagenidium and placed in the primarily plant parasitic genus Pythium.
Abstract
Over the past twenty years, infections caused by previously unrecognised oomycete
pathogens with morphological and molecular similarities to known Lagenidium species
have been observed with increasing frequency, primarily in dogs but also in cats and
humans. Three of these pathogens were formally described as Lagenidium giganteum
forma caninum, Lagenidium deciduum, and Paralagenidium karlingii in advance of published
phylogenetic verification. Due to the complex nature of Lagenidium taxonomy
alongside recent reports of mammalian pathogenic species, these taxa needed to be
verified with due consideration of the available data for Lagenidium and its allied genera.
This study does so through morphologic characterisation of the mammalian pathogenic
species, and phylogenetic analyses. The six-gene phylogeny generally supports the
most recent comprehensive classification of Lagenidium with a well-supported Lagenidium
clade that includes the mammalian pathogens L. giganteum f. caninum and L. deciduum,
and well-supported clades for which the names Myzocytiopsis and Salilagenidium
can be applied. The genus Paralagenidium is phylogenetically unrelated to any of the
main clades within the class Peronosporomycetes. Close relationships between pathogens
of mammals and those of insects or nematodes were revealed. Further characterisation
of Lagenidium-like taxa is needed to establish the risk of mammalian infection by
pathogens of insects and nematodes.