Sterols of the Green‐Pigmented, Freshwater Raphidophyte, Gonyostomum semen, from Scandinavian Lakes

Abstract

Sterols are a class of membrane-reinforcing, ringed lipids which have a long history of examination in algae as a means of deriving chemotaxonomic relationships and as potential lipidic biomarkers. The Raphidophyceae represent a class of harmful, bloom-forming, marine and freshwater algae. To date, there have been four published examinations of their sterol composition, focusing primarily on brown-pigmented, marine species within the genera, Chattonella, Fibrocapsa, and Heterosigma. Lacking in these examinations has been the species Gonyostomum semen Ehrenb., which is a green-pigmented, freshwater raphidophyte with a worldwide distribution. The goal of this study was to examine the sterol composition of this nuisance alga, determine the potential of using its sterol profile as a biomarker, and finally to determine if there is any intraspecific variability between isolates. We have examined 21 isolates of G. semen from a number of Scandinavian lakes, and all were found to produce two major sterols, 24-ethylcholesta-5,22E-dien-3β-ol and 24-ethylcholest-5-en-3β-ol, and 24-methylcholest-5-en-3β-ol as a minor sterol; the presence of 24-ethylcholesta-5,22E-dien-3β-ol differentiates G. semen from brown-pigmented, marine raphidophytes which generally lack it. The results of this study indicate that isolates of G. semen from geographically separate lakes across Finland and Scandinavia have the same sterol biosynthetic pathway, and that there is no evolutionary divergence between the isolates with regard to sterol composition. The sterols of G. semen are not considered to be useful biomarkers for this particular organism because they are commonly found in other algae and plants.

Pigment composition and photoacclimation as keys to the ecological success of Gonyostomum semen (Raphidophyceae, Stramenopiles)

“…This hypothesis is supported by differences in fatty acid and sterol composition between brown‐pigmented, marine raphidophytes and green‐pigmented species ( Gonyostomum and Vacuolaria ; Roche and Leblond , Leblond et al. ). However, further ultrastructural studies are needed to confirm tertiary endosymbiosis in the freshwater lineages.…”

Suitability of Phytosterols Alongside Fatty Acids as Chemotaxonomic Biomarkers for Phytoplankton

“…There is a great diversity of sterols in Diatomophyceae, but none of them are found exclusively in diatoms (Rampen et al, 2010 ). For example brassicasterol is also a major sterol in Cryptophyceae (Rampen et al, 2010 ) and stigmasterol, and β-sitosterol are typical for Chrysophyceae and Raphidophyceae in addition to Diatomophyceae (Cranwell et al, 1988 ; Rampen et al, 2010 ; Leblond et al, 2013 ).…”