Diurnal Cycling of Triacylglycerides in a Chlorophyte Sp.: Implications for the Production of Algal Biofuels

There is no doubt that crude oil will be depleted eventually. The concept of global warming is now well accepted. Given these twin constraints, it behooves us to find alternative fuels, especially liquid ones for transportation. Microalgae have the potential to both reduce increases in greenhouse gases and provide an energy dense fuel. The world-wide nascent industry in algal biofuels lacks basic physiological information concerning organisms that might be used in an oil production effort. Neutral lipids such as triacylglycerides are formed in algal batch cultures as growth progresses. Biology in general utilizes such molecules as alternative stored energy sources when the primary energy source, e.g., photosynthesis, is not available such as in darkness. We postulate that what we see in algae is the result of TAG accumulation which is the remainder after utilization has taken place. It is unlikely that this phenomenon will be recognized unless cell division synchronized cells are investigated. Our data using Chlorella indicate that TAG accumulation, as evidenced by Nile Red fluorescence, increases in the light and decreases in the dark and is tied to the time when the cells divide. Most aerobic organisms use the Krebs tricarboxylic cycle pathway to metabolize C-2 fragments derived from the fatty acids found in TAGs. Inhibition of this pathway by trifluoroacetate in Chlorella and some diatoms inhibits TAG utilization leading to an increase in TAG accumulation. This phenomenon is important in deciding when an oil accumulating algal culture should be harvested and provides at least two points where metabolic regulation could be altered to increase oil accumulation.&'