Increasing lipid accumulation in microalgae through environmental manipulation, metabolic and genetic engineering: a review in the energy NEXUS framework

Abstract

Microalgae have long been seen as a suitable alternative to a range of products like nutraceuticals, cosmetics, food additives, and as a feedstock for biofuels, attributable to their rapid growth rate, high photosynthetic efficiency, simple growth requirements, and accumulation of valuable products. Given the increasingly severe global threat of climate change, microalgal biofuels like biodiesel remain one of the most sought-after products. Microalgae pose a favorable alternative to current first and second generations biofuels, for unlike them, algae do not require arable land or potable water to grow, thus sparing the competition for precious natural resources. In addition, many strains of microalgae boast a significantly higher lipid content than other feedstocks, at a minimum of 15 to 20 times higher than land-based oleaginous crops. However, despite global R&D efforts, they are yet to be commercialized. Challenges associated with microalgae development include inadequate lipid productivity to meet commercial needs and that microalgae frequently display a high lipid production at the expense of the growth rate, or vice versa. One avenue through which a remedy to this issue is being pursued is metabolic and genetic engineering, which attempts to increase the feasibility of using microalgae as a next-generation feedstock for biodiesel and the like through enhanced lipid, or triacylglycerol, content. In this review, several approaches geared towards increasing lipid accumulation and production such as the control of cultivation conditions, inducing nutrient starvation, and the use of metabolic and genetic manipulation techniques are outlined. This must be done ensuring biosafety.