Aggregate formation and polysaccharide content of Chlorella pyrenoidosa Chick (Chlorophyta) in response to simulated nutrient stress

To determine how polysaccharide production influences microalgal aggregate size, we stimulated polysaccharide production using existing methods (previously applied to cyanobacteria and plants). Cultures were treated with glyoxylate (0, 0.25, 0.5, 1.25 mmol/L) to simulate nutrient stress and examined for 9 days (approaching stationary phase on day 9) to assess: growth rate, polysaccharide production (soluble, bound, and total), aggregate size, and the relation between polysaccharide and aggregate size. We found: 1.25 mmol/L glyoxylate inhibits growth, but 0.25 and 0.5 mmol/L do not, allowing comparisons of aggregate formation at lower concentrations; glyoxylate-induced polysaccharide production, which increased with increased glyoxylate concentration and time; an increase in relative abundance of cells bound together with increased glyoxylate addition; and increased glyoxylate-stimulated polysaccharide levels were directly correlated with aggregate size. This study indicates that glyoxylate may be used to examine microalgal ecophysiology and offers a method to predict the influence of nutrient stress on polysaccharide production.