Use of sodium bicarbonate to stimulate triacylglycerol accumulation in the chlorophyte Scenedesmus sp. and the diatom Phaeodactylum tricornutum

Abstract

There is potential for algal-derived biofuel to help alleviate part of the world’s dependency on petroleum based fuels. However, research must still be done on strain selection, induction of triacylglycerol (TAG) accumulation, and fundamental algal metabolic studies, along with large-scale culturing techniques, harvesting, and biofuel/biomass processing. Here, we have advanced the knowledge on Scenedesmus sp. strain WC-1 by monitoring growth, pH, and TAG accumulation on a 14:10 light–dark cycle with atmospheric air or 5% CO2 in air (v/v) aeration. Under ambient aeration, there was a loss of pH-induced TAG accumulation, presumably due to TAG consumption during the lower culture pH observed during dark hours (pH 9.4). Under 5% CO2 aeration, the growth rate nearly doubled from 0.78 to 1.53 d−1, but the pH was circumneutral (pH 6.9) and TAG accumulation was minimal. Experiments were also performed with 5% CO2 during the exponential growth phase, which was then switched to aeration with atmospheric air when nitrate was close to depletion. These tests were run with and without the addition of 50 mM sodium bicarbonate. Cultures without added bicarbonate showed decreased growth rates with the aeration change, but there was no immediate TAG accumulation. The cultures with bicarbonate added immediately ceased cellular replication and rapid TAG accumulation was observed, as monitored by Nile Red fluorescence which has previously been correlated by gas chromatography to cellular TAG levels. Sodium bicarbonate addition (25 mM final concentration) was also tested with the marine diatom Phaeodactylum tricornutum strain Pt-1 and this organism also accumulated TAG.