The recently described thraustochytrid diatom parasite Phycophthorum isakeiti has been isolated from the marine system of northern Norway (Hassett, 2020). Protist P. isakeiti’s ecological role, biodiscovery potential, and interactions with a possible diatom host, Pleurosigma sp. remain largely unexplored. Here I present culturing experiments to test whether P. isakeiti is an obligate parasite. To ...