title: A new flagellated dispersion stage inParaphysoderma sedebokerense, a pathogen ofHaematococcus pluvialis.
abstract: The blastocladialean fungusParaphysoderma sedebokerenseBoussiba, Zarka and James is a devastating pathogen of the commercially valuable green microalgaHaematococcus pluvialis, a natural source of the carotenoid pigment astaxanthin. First identified in commercialHaematococcuscultivation facilities,P. sedebokerenseis hypothesised to have a complex life cycle that switches between a vegetative and a resting phase depending on favourable or unfavourable growth conditions. Rather unusually for blastocladialean fungi,P. sedebokerensewas described as lacking flagellated zoospores and only propagating via aplanosporic amoeboid cells. However, during repeated microscopic observation ofP. sedebokerensecultivated in optimal conditions, we detected fast-swimming, transiently uniflagellated zoospores which rapidly transform into infectious amoeboid swarmers, the existence of which suggests a closer than previously thought relatedness ofP. sedebokerenseto its sister generaPhysodermaandUrophlyctis. Additionally, we found some morphological and physiological differences between amoeboid swarmers and discuss hypotheses about their significance. These amoeboid and flagellated propagules are key to the dissemination ofP. sedebokerenseand are probably also the life stages most vulnerable to adverse environmental conditions. They are therefore a prime target for the development of disease management protocols in industrial cultivation facilities, a goal which requires a detailed understanding of their physiology.
authors.affiliation: Scottish Marine Institute, Scottish Association for Marine Science, Oban, Argyll PA37 1QA UK.
authors.forename: Martina
authors.initials: M
authors.lastname: Strittmatter
authors.affiliation: A4F-Algae For Future SA, Campus do Lumiar-Edifício E-R/C, Estrada do Paço do Lumiar, 1648-038 Lisbon, Portugal.
authors.forename: Tiago
authors.initials: T
authors.lastname: Guerra
authors.affiliation: A4F-Algae For Future SA, Campus do Lumiar-Edifício E-R/C, Estrada do Paço do Lumiar, 1648-038 Lisbon, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Silva
authors.affiliation: Scottish Marine Institute, Scottish Association for Marine Science, Oban, Argyll PA37 1QA UK.
authors.forename: Claire M M
authors.initials: CM
authors.lastname: Gachon
keywords: Amoebae; Blastocladiales; Flagellum; Green alga; Life cycle; Pathogen; Zoospores