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

Abstract

Successful algal cultivation for biofuel production is one path in the transition to a renewable energy economy. The green alga Scenedesmus dimorphus is a candidate for biofuel production, but is subject to parasitism and subsequent population crash when cultivated in open ponds. From an open pond cultivating S. dimorphus for biofuel production in New Mexico, USA, an amoeboid parasite was isolated, designated as isolate FD61, and its rDNA operon sequenced. A BLAST search for nuc 18S rDNA (18S) sequence similarity identified the parasite as Paraphysoderma sedebokerense (Blastocladiomycota). Here, we examine the ultrastructure of P. sedebokerense and compare it with that of a sister taxon, Physoderma maydis. The parasite has thin-walled vegetative sporangia and thick-walled resting sporangia. Our observations indicate that amoeboid swarmers are produced in the vegetative phase, while either amoeboid swarmers or zoospores are the product of meiosis in resting sporangia. Meiosis is confirmed by the presence of synaptonemal complexes in resting sporangia nuclei. Notably, P. sedebokerense has a Golgi apparatus with stacked cisternae, a feature reported for P. maydis, but which is absent in all other examined taxa in Blastocladiomycota. This report furthers our knowledge of the life cycle of P. sedebokerense.

Morphology, Ultrastructure, and Molecular Phylogeny of Rozella multimorpha, a New Species in Cryptomycota

“…This procedure was repeated approximately 100 times over a period of 6 d to accumulate an adequate sample of zoospores for TEM examination. The glutaraldehyde/buffer/zoospore suspension was processed as described in Letcher et al (2016).…”

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

“…Amongst those examples is Paraphysoderma sedebokerense Boussiba, Zarka & T.Y. James, a blastocladialean fungus that parasitises the green microalgae Haematococcus pluvialis Flotow 1844 and Scenedesmus dimorphus (Turpin) Kützing 1834 (Gutman et al 2009;James et al 2012;Letcher et al 2016). These two species are of commercial interest: Haematococcus pluvialis produces high quantities of astaxanthin, a carotenoid with a high market value that is widely used in cosmetics, aquaculture food, nutraceuticals, and human consumption (reviewed by Shah et al 2016).…”

“…Patnaik et al 2019;Zhang et al 2015). Whereas both species can be cultivated on an industrial scale, frequent culture crashes evoked by the pathogen P. sedebokerense represent bottlenecks in algal biomass production and entail significant economic losses (Hoffman et al 2008;Letcher et al 2016).…”

“…The life cycle of this green algal pathogen, Paraphysoderma, is only partially understood (Hoffman et al 2008;Letcher et al 2016;Strittmatter et al 2016). This fungus can grow both saprophytically and parasitically on various green algal hosts, but we do not yet know: (1) the factors that trigger the transition from one life cycle stage to the other; (2) its ploidy; or, (3) the full diversity of its various life cycle stages.…”

“…Thus, we set out to develop a more sophisticated cryopreservation strategy ( Fig. S1) using two strains of Paraphysoderma, PS1 and FD61, previously described (Letcher et al 2016;Strittmatter et al 2016). Strain PS1 was maintained on agar together with its host H. pluvialis Haem C1 (Strittmatter et al 2016), whereas strain FD61 was exclusively maintained on agar.…”