Cellular cycling, carbon utilization, and photosynthetic oxygen production during bicarbonate-induced triacylglycerol accumulation in a Scenedesmus sp.

Microalgae are capable of synthesizing high levels of triacylglycerol (TAG) which can be used as precursor compounds for fuels and specialty chemicals. Algal TAG accumulation typically occurs when cellular cycling is delayed or arrested due to nutrient limitation, an environmental challenge (e.g., pH, light, temperature stress), or by chemical addition. This work is a continuation of previous studies detailing sodium bicarbonate-induced TAG accumulation in the alkaline chlorophyte Scenedesmus sp. WC-1. It was found that upon sodium bicarbonate amendment, bicarbonate is the ion responsible for TAG accumulation; a culture amendment of approximately 15 mM bicarbonate was sufficient to arrest the cellular cycle and switch the algal metabolism from high growth to a TAG accumulating state. However, the cultures were limited in dissolved inorganic carbon one day after the amendment, suggesting additional carbon supplementation was necessary. Therefore, additional abiotic and biotic experimentation was performed to evaluate in- and out-gassing of CO₂. Cultures to which 40-50 mM of sodium bicarbonate were added consumed DIC faster than CO₂ could ingas during the light hours and total photosynthetic oxygen production was elevated as compared to cultures that did not receive supplemental inorganic carbon.