Control of triacylglycerol accumulation and bicarbonate-induced accumulation in microalgae

Abstract

Microalgae are capable of accumulating high levels of lipids and starch as carbon storage compounds. Investigation into the metabolic activities involved in the synthesis of these compounds has escalated since these compounds can be used as precursors for food and fuel. This dissertation represents the summary of work completed to evaluate factors that control and stimulate triacylglycerol (TAG) accumulation in microalgae, and demonstrate the use of sodium bicarbonate as a chemical additive to induce TAG accumulation. Two Chlorophytes, Scenedesmus sp. WC-1 and Coelastrella sp. PC-3, were analyzed in pH buffered systems to determine the effect of pH on growth and TAG accumulation, both with and without nitrate deplete conditions. Medium nitrate and pH were found to be independent stress mechanisms and the causal effects of each were determined. Growth and TAG accumulation was optimized on the Chlorophyte Scenedesmus sp. WC-1 and the addition of bicarbonate was shown to arrest cellular replication and induce an elevated TAG accumulation rate. Thus, decreasing the total culturing time required for TAG production by half. To ascertain whether the addition of bicarbonate would give similar results in other algae, the marine diatom Phaeodactylum tricornutum Pt-1 and the model Chlorophyte Chlamydomonas reinhardtii were evaluated similar to WC-1. C. reinhardtii showed a cessation of the cell cycle with bicarbonate addition while P. tricornutum Pt-1 did not. However, the addition of bicarbonate was shown to induce lipid accumulation in both organisms. This demonstrates the broad use of bicarbonate as a means of inducing TAG accumulation in microalgae (Chlorophytes and diatoms, freshwater or marine).