Lipid composition of Chlorella vulgaris (Trebouxiophyceae) as a function of different cadmium and phosphate concentrations

Fatty acids are the fundamental structural components of membrane lipids, and the degree of saturation of the long hydrocarbon chains in microalgae contributes to regulation of growth, biomass production and reproduction of aquatic consumers. This research aimed at evaluating the effects of cadmium (2 x 10(-8); 10(-7) mol L-1 Cd) on lipid class and fatty acid composition of the microalga Chlorella vulgaris under varying phosphate (PO43-) concentrations (6.0 x 10(-7) to 2.3 x 10(-4) mol L-1). Under PO43- limitation and Cd stress, the storage lipid class triacylglycerol (TAG) was the most accumulated among the lipid classes. Fatty acid composition revealed that the degree of saturation increased with increasing Cd stress and PO43- limitation. Decreasing PO43- and increasing Cd concentrations resulted in higher saturated fatty acid (SAFA) and monounsaturated FA (MUFA) concentrations. Total polyunsaturated FA (PUFA) and omega 3 PUFA, and PUFA:SAFA ratios were higher in the control (2.3 x 10(-4) mol L-1 PO43-) cells than in either PO43- limitation or Cd stress, or in the combination of both stresses. Contrasting with all the other PUFAs, 18:2n - 6 increased as PO43- limitation increased. A significant positive relationship of PUFAs, acetone mobile polar lipids (AMPL) and phospholipids (PL) with phosphate concentration in the culture media was obtained, while TAG concentrations had a positive association with total MUFA and SAFA. Total SAFA, 14:0, 18:1n - 9 and 18:2n - 6 were positively correlated with Cd and negatively with PO43- concentrations. The microalga responded to combined PO43- limitation and Cd exposure by increasing its total lipid production and significantly altering its lipid composition. The FA 18:2n - 6 may be considered a stress biomarker for PO43- limitation and Cd stress in C. vulgaris. (c) 2012 Elsevier B.V. All rights reserved. (AU)