A new flagellated dispersion stage in Paraphysoderma sedebokerense, a pathogen of Haematococcus pluvialis

Abstract

The blastocladialean fungus Paraphysoderma sedebokerense Boussiba, Zarka and James is a devastating pathogen of the commercially valuable green microalga Haematococcus pluvialis, a natural source of the carotenoid pigment astaxanthin. First identified in commercial Haematococcus cultivation facilities, P. sedebokerense is 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. sedebokerense was described as lacking flagellated zoospores and only propagating via aplanosporic amoeboid cells. However, during repeated microscopic observation of P. sedebokerense cultivated 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 of P. sedebokerense to its sister genera Physoderma and Urophlyctis. 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 of P. sedebokerense and 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.Electronic supplementary materialThe online version of this article (doi:10.1007/s10811-015-0700-8) contains supplementary material, which is available to authorized users.

Parallelisable non-invasive biomass, fitness and growth measurement of macroalgae and other protists with nephelometry

“…Phaeocystis sp., Alexandrium minutum (RCC1490), Guinardia flaccida (RCC3088) were kindly gifted by the Roscoff Culture Collection. The axenic Paraphysoderma sedebokerense strain PS1 was subcultured every 3-4 weeks to fresh liquid chytrid growth medium as detailed in Strittmatter et al [21].…”

An ultrastructural study of Paraphysoderma sedebokerense (Blastocladiomycota), an epibiotic parasite of microalgae

“…Haematococcus pluvialis is cultivated commercially for a variety of products, including biofuels (Brennan andOwende 2009, Razon andTan 2011). The parasite was first reported from Israel (Hoffman et al 2008), later in Portugal (Strittmatter et al 2015), and with our isolate of P. sedebokerense, now is known to occur in the US. Thus, distribution of the parasite may be world-wide and a potential threat to microalgae culture and biofuel production in numerous geographical locations.…”

“…Few instances of non-flagellate motile spores have been reported in Chytridiomycota (Sparrow 1960), and prior to P. sedebokerense, none in Blastocladiomycota. In a recent publication, Strittmatter et al (2015) observed flagellated spores and conjugation of amoeboid swarmers.…”

“…evolved a variety of life cycle strategies(James et al 2014).Our understanding of the complexity of the life cycle of Paraphysoderma sedebokerense is increasing(Strittmatter et al 2015), but details remain to be resolved. In first characterizing P. sedebokerense,Hoffman et al (2008) illustrated thin-walled and thick-walled sporangia and reported only amoeboid swarmers.…”

Ionic liquid as an effective solvent for cell wall deconstructing through astaxanthin extraction from Haematococcus pluvialis

“…Under environmental stress, the morphological physiology of H. pluvialis transforms from unicellular biflagellate microalga to mature red-coloured, non-motile cysts, also the accumulation of astaxanthin and the formation of non-motile aplanospores with elaborated three-layers cell wall, which consists of a thick, hydrolysis-resistant outer layer (trilaminar sheath), a polysaccharide homogeneous arrangement middle layer (secondary wall) and polysaccharide heterogeneous arrangement inner layer (tertiary wall) (Cheng et al, 2016;Strittmatter et al, 2016). The outermost trilaminar sheath is characterised by a tough, non-hydrolysable, sporollenin-like polymer known as algaenan, by making H. pluvialis extremely resistant to mechanical and chemical pretreatment cell disruption process, and might be complicated extraction of astaxanthin (Montsant et al, 2001;Hagen et al, 2002;Damiani et al, 2006).…”