The effect of high pH on structural lipids in diatoms

We tested the hypothesis that increased pH reduces the amount of structural lipids. To do this, we used three different diatoms (Phaeodactylum tricornutum CCAP strain, P. tricornutum TV strain and Amphiprora sp). We tested the effect of rapid increase from pH 7.5 to 10 by adding NaOH. The total lipid content was reduced by 13, 36 and 47 % in the P. tricornutum CCAP strain, TV strain and Amphiprora sp., respectively, 1 h after increasing the pH. The P. tricornutum CCAP strain was used for further testing the effect of pH on the lipid content during active growth. This strain was cultivated at pH 7.5 and 10, and the pH was regulated by the CO₂ inflow. The growth rate was similar (0.3 day⁻¹) in both pH treatments, but the lipid content in the pH 10 treatment was on average 28 % lower than in the pH 7.5 treatment. Our data support the hypothesis that structural lipids are reduced when pH increases to high levels. The results suggest that regulating the pH during algae cultivation could be used to refine the lipid composition in the harvested algal biomass.