The limited fossil fuel resources along with the need to reduce Green House Gas emissions were a major impulse to the development of alternative fuels. As a result, increased attention has been given to biofuels, such as biodiesel, that can be used as an alternative fuel in compression-ignition engines. Its production from renewable resources, such as vegetable oils and animal fats, makes it biodegradable and non-toxic; also, it contributes to the reduction of CO2 emissions, because it comprises a closed carbon cycle.
The transesterification process is a reversible reaction and carried out by mixing the reactants-fatty acids, alcohol and catalyst. A strong base or a strong acid can be used as a catalyst. At the industrial scale, mostly sodium or potassium methanolate is used. The end products of the transesterification process are raw biodiesel and raw glycerol. In a further process these raw products undergo a cleaning step. In case of using methanol as alcohol FAME (fatty acid methyl ester) biodiesel is produced.
Microalgae produce biomass using sunlight, water and carbon dioxide by the process of photosynthesis. The biomass production rate of many microalgal species generally exceeds that of land plants. Microalgae store energy in storage molecules, such as neutral lipids that form cytoplasmic lipid droplets (LDs). The accumulated lipid is mainly in the form of triacylglycerols (TAGs), which can be used for biodiesel production. In contrast to corn-based ethanol or soy- and palm-based biodiesel, biofuels derived from microalgal feedstocks can be produced free of competition with resources used for agricultural food production. Moreover, microalgae can grow under severe environmental conditions and thus can be cultivated with many types of culture systems on an industrial scale. Due to these reasons, microalgae have attracted considerable interest as a promising biofuel resource.
Glycerol-3-Phosphate Acyl-Transferase (GPAT) family as a promising target for increasing Biofuel production from the Red alga Cyanidioschyzon merolae.
Algae are known to store up large amounts of oils called triacylglycerols (TAGs) under adverse conditions such as nitrogen deprivation. Understanding precisely how they do so is of key interest to the biotechnology sector, as TAGs can be converted to biodiesel. To this end, scientists are investigating the unicellular red alga C. merolae as a model organism for exploring how to improve TAG production.
A study led by Sousuke Imamura at the Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology (Tokyo Tech), has now shown that an enzyme called GPAT1 plays an important role in TAG accumulation in C. merolae even under normal growth conditions-that is, without the need to induce stress.
Remarkably, the team demonstrated that TAG productivity could be increased by more than 56 times in a C. merolae strain overexpressing GPAT1 compared with the control strain, without any negative effects on algal growth.
Their findings, published in Scientific Reports, follow up previous research by Imamura and others that had suggested two GPATs, GPAT1 and GPAT2, may be closely involved in TAG accumulation in C. merolae.
The results indicate that the reaction catalyzed by the GPAT1 is a rate-limiting step for TAG synthesis in C. merolae, and would be a potential target for improvement of TAG productivity in microalgae.
The team plans to continue exploring how GPAT1 and GPAT2 might both be involved in TAG accumulation. An important next step will be to identify transcription factors that control the expression of individual genes of interest.
TAG productivity will be further improved if researchers can identify such regulators and modify their function, because transcription factors affect the expression of a wide range of genes including GPAT1-related genes. This kind of approach based on the fundamental molecular mechanism of TAG synthesis should lead to successful commercial biofuel production using microalgae.