Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances

Abstract

SummaryMicroalgae represent an exceptionally diverse but highly specialized group of micro-organisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g. 20-50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Fatty acids, the building blocks for TAGs and all other cellular lipids, are synthesized in the chloroplast using a single set of enzymes, of which acetyl CoA carboxylase (ACCase) is key in regulating fatty acid synthesis rates. However, the expression of genes involved in fatty acid synthesis is poorly understood in microalgae. Synthesis and sequestration of TAG into cytosolic lipid bodies appear to be a protective mechanism by which algal cells cope with stress conditions, but little is known about regulation of TAG formation at the molecular and cellular level. While the concept of using microalgae as an alternative and renewable source of lipid-rich biomass feedstock for biofuels has been explored over the past few decades, a scalable, commercially viable system has yet to emerge. Today, the production of algal oil is primarily confined to high-value specialty oils with nutritional value, rather than commodity oils for biofuel. This review provides a brief summary of the current knowledge on oleaginous algae and their fatty acid and TAG biosynthesis, algal model systems and genomic approaches to a better understanding of TAG production, and a historical perspective and path forward for microalgae-based biofuel research and commercialization.

Scenedesmus sp. NJ-1 isolated from Antarctica: a suitable renewable lipid source for biodiesel production

“…The oil droplets in Scenedesmus NJ-1 may also serve as a reserve of energy in the form of TAGs. It has been reported that the contents of lipids and TAGs can be affected by nutrient stress, growth phases and/or the aging of cultures (Hu et al 2008b). In this study, large amounts of TAGs accumulated at the late phase of batch culture with low concentration of nitrogen.…”

“…Therefore, lipids from Phase II (with 78 % NL) might be good feedstock for biodiesel production. The significant decrease in GL and PL contents of the Phase II cells may be attributed to the long exposure to nitrogen starvation, which stimulated hydrolysis of GL and PL and converted these polar lipids into NL (Hu et al 2008b). In Scenedesmus obliquus, the highest lipid productivity was achieved by pre-culture in glucose-supplemented medium before it was transferred to the media deficient in nitrate and phosphate (Mandal and Mallick 2009).…”

“…Many microalgal species such as diatoms and chlorophyceae have been identified as oleaginous algae (Hu et al 2008b). For example, Scenedesmus, belonging to chlorophyceae, has been found to contain high content of lipids (Li et al 2011;Abou-Shanab et al 2011) and shows the potential to remove inorganic nutrients from waste water (Li et al 2010).…”

Transcript level coordination of carbon pathways during silicon starvation‐induced lipid accumulation in the diatom Thalassiosira pseudonana

“…N, phosphorus) induces the formation of triacylglycerol‐rich lipid droplets coincident with an arrest in growth (Hu et al ., 2008; Yu et al ., 2009). Silicon is required for cell wall synthesis and growth in most diatoms, and silicon starvation also induces growth arrest and the formation of lipid droplets (Shifrin & Chisholm, 1981; Roessler, 1988; Traller & Hildebrand, 2013).…”

An Overview of Algae Biofuel Production and Potential Environmental Impact

“…4−6 Hu et al (2008) projected a possible yield of 200 barrels of oil per hectare (2.47 acres) of land used for growing photosynthetic algae. 5 This theoretical maximum algae yield is 100 times greater than that for soybeans, a commonly used feedstock for biodiesel, and is greater than any demonstrated yield (by a factor of 10−20), but should be a goal for the rapidly developing algae industry. 5 Algae-based biofuel production has a number of potential advantages:…”