Microalgal lipids: A review of lipids potential and quantification for 95 phytoplankton species

Phytoplankton have great potential for biodiesel production and offer promises and opportunities in the long term. Phytoplankton species reach higher growth rates, and thus productivity, than conventional forestry or agricultural crops and other aquatic plants. The oil yield in phytoplankton is an order of magnitude larger than terrestrial oleaginous crops. To meet the potential of phytoplankton-based biodiesel there is a need to radically increase lipid yields, which are generally produced under adverse conditions. Nutrients stress and alterations of cultivation conditions are commonly used as lipid enhancement strategies. It is difficult to get a clear picture of the most efficicent factors affecting lipid accumulation and productivity from the abundant literature on this topic, dispatched into a large variety of species and stresses. This article seeks to summarize the widely reported information on TAGs accumulation in phytoplankton and to decipher the regulation mechanisms triggered along the diversity of enhancement strategies. Most of the factors affecting lipid content and composition were analyzed, such as nutrient starvation, temperature, irradiance, salinity, oxidative stress, metals, CO₂ flux, pH and metabolic engineering. In this review, we compiled 213 experiments with lipid analysis, dealing with 95 marine and freshwater phytoplankton (microalgae and cyanobacteria) species. Quantitative indicators (lipid content and productivity), stress level and exposure time, are presented. This review highlights the complexity of comparison between phyla due to differences in culture conditions, analytical methods and/or growth phase. It provides valuable tools for triggering phytoplanktonic lipid biosynthesis and opens the door for enhanced quality and quantity of phytoplankton-based biodiesel.