Retracing Storage Polysaccharide Evolution in Stramenopila

Abstract

Eukaryotes most often synthesize storage polysaccharides in the cytosol or vacuoles in the form of either alpha (glycogen/starch)- or beta-glucosidic (chrysolaminarins and paramylon) linked glucan polymers. In both cases, the glucose can be packed either in water-soluble (glycogen and chrysolaminarins) or solid crystalline (starch and paramylon) forms with different impacts, respectively, on the osmotic pressure, the glucose accessibility, and the amounts stored. Glycogen or starch accumulation appears universal in all free-living unikonts (metazoa, fungi, amoebozoa, etc.), as well as Archaeplastida and alveolata, while other lineages offer a more complex picture featuring both alpha- and beta-glucan accumulators. We now infer the distribution of these polymers in stramenopiles through the bioinformatic detection of their suspected metabolic pathways. Detailed phylogenetic analysis of key enzymes of these pathways correlated to the phylogeny of Stramenopila enables us to retrace the evolution of storage polysaccharide metabolism in this diverse group of organisms. The possible ancestral nature of glycogen metabolism in eukaryotes and the underlying source of its replacement by beta-glucans are discussed.

Nutritional value of microalgae for ruminants and implications from microalgae production

“…In contrast, there is huge variation in the form of storage carbohydrates between different microalgae genera and it may even vary from species to species within the genera. Sometimes the storage polysaccharides of microalgae are simply stated to contain either α (glycogen or starch) or β-linked (chrysolaminarins and paramylon) glucose molecules (glucan), of which glycogen and chrysolaminarins are water-soluble and starch and paramylon solid crystalline forms [268]. However, as we see in the following section, and which was also demonstrated in [268], microalgal storage polysaccharides are much more complex.…”

“…Sometimes the storage polysaccharides of microalgae are simply stated to contain either α (glycogen or starch) or β-linked (chrysolaminarins and paramylon) glucose molecules (glucan), of which glycogen and chrysolaminarins are water-soluble and starch and paramylon solid crystalline forms [268]. However, as we see in the following section, and which was also demonstrated in [268], microalgal storage polysaccharides are much more complex. The http://www.cabi.org/cabreviews structural features of storage polysaccharides (e.g.…”

“…Bacillariophyta, Haptophyta and Ochrophyta store carbohydrates as a chrysolaminarin [91,268,290]. Chrysolaminarin is predominantly β-(1,3) linked glucan with occasional β-(1,2), β-(1,4) or β-(1,6) branching, and is easily extractable by dilute acid or hot water [291].…”

“…Nitrogen limitation and high light intensities also promote the accumulation of chrysolaminarin (up to 500 g/kg DM) in diatoms [291]. Ochrophyta have no ability to metabolise α-glucans [268]. Some studies have reported small amounts of α-linked glucose in Bigyra (Table 1).…”

“…Some studies have reported small amounts of α-linked glucose in Bigyra (Table 1). However, the storage polysaccharide metabolism of this phylum is largely unknown, as according to phylogenetic analysis of enzymes involved Bigyra have lost the ability to both α-and β-glucan metabolism [268].…”