Characterization of three novel species of Labyrinthulomycota isolated from ochre sea stars (Pisaster ochraceus)

Abstract

The Labyrinthulomycota (Stramenopiles) is an enigmatic group of saprobic protists that play an important role as marine decomposers, yet whose phylogenetic relationships and ecological roles remain to be clearly understood. We investigated whether members of this group were present on ochre sea stars (Pisaster ochraceus) showing symptoms of sea star wasting disease. Although largely decomposers, some members of the Labyrinthulomycota are also known to be opportunistic pathogens of animals such as abalone, clams and flatworms and cause severe wasting diseases in eelgrass populations worldwide. Three new isolates of Labyrinthulomycota were discovered from the tissues of P. ochraceus collected at Bamfield Marine Research Centre (48°83.6′N, 125°13.6′W) and Reed Point Marina (49°29.1′N, 122°88.3′W) in British Columbia. The new isolates were kept in culture for several months and characterized at the morphological level and with 18S rDNA sequences. Molecular phylogenetic analyses demonstrated that each of the three new isolates clustered within a different subclade of the Labyrinthulomycota: (1) Oblongichytrium, (2) Aplanochytrium and (3) an early diverging clade of environmental DNA sequences. These data enabled us to establish one new genus and three new species of Labyrinthulomycota: Stellarchytrium dubum gen. et sp. nov., Oblongichytrium porteri sp. nov. and Aplanochytrium blankum sp. nov. This is the first account of the Labyrinthulomycota isolated from the tissues of sea stars with a potential link to sea star wasting disease reported for P. Ochraceus.