Cryopreservation of the parasitic and saprophytic life stage of the blastocladialean pathogen Paraphysoderma sedebokerense infecting the green algae Haematococcus pluvialis and Scenedesmus dimorphus

Host–pathogen interactions involving microalgae have attracted more and more interest over the past decade. In order to understand interactions between those two partners and as basis of each single experiment, biological material in the form of cultures is crucial. Whereas the establishment of such cultures can by itself be very difficult and time-consuming, their subsequent maintenance often requires as much effort and manpower. The commercially utilised green microalgae Haematococcus pluvialis and Scenedesmus dimorphus are often challenged by the blastocladialean fungus Paraphysoderma sedebokerense, leading to culture crashes and economic loss. Currently, the interaction between alga and pathogen as well as the life cycle of the fungus are only partially understood. This represents a bottleneck and risk for the maintenance via continuous subcultivation. We here report the development of a cryopreservation protocol for Paraphysoderma sedebokerense and show its applicability to two different life stages of the pathogen. This protocol was validated on two different strains of Paraphysoderma.