Nannochloropsis Lipids and Polyunsaturated Fatty Acids: Potential Applications and Strain Improvement

Abstract

The genus Nannochloropsis comprises a group of oleaginous microalgae that accumulate polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA). These molecules are essential for the correct development and health of humans and animals. Thanks to their attractive lipid profile, Nannochloropsis is mainly marketed as a feed ingredient in aquaculture. In microalgae of this genus, contents and cellular location of PUFAs are affected by the growth conditions and gene expression. Strain improvement through non-recombinant approaches can generate more productive strains and efficient bioprocesses for PUFA production. Nevertheless, the lack of specific markers, detection methods, and selective pressure for isolating such mutants remains a bottleneck in classical mutagenesis approaches or lipid quality assessment during cultivation. This review encompasses the importance of PUFAs and lipid classes from Nannochloropsis species and their potential applications. Additionally, a revision of the different ways to increase PUFA content in Nannochloropsis sp. by using classical mutagenesis and adaptive laboratory evolution is also presented, as well as various methods to label and quantify lipids and PUFAs from Nannochloropsis microalgae.

Keywords: Nannochloropsis; PUFA applications; PUFA quantification; algal lipid analysis; strain improvement.

Figure 3

Proposed model of a Nannochloropsis cell including the location of the different lipid classes. This model is supported with studies on physiology and cellular organisation of Nannochloropsis [73,74,75,76,77]. Organelles—C: cytosol; Ch: chloroplast; ER: endoplasmic reticulum; M: mitochondria; N: nucleus; OB: oil bodies; RB: red body. Lipid classes—DAG: diacylglycerol; DGDG: digalactosyldiacylglycerol; DGTS: diacylglycerol–trimethyl–homoserine; MGDG: monogalactosyldiacyglycerol; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PG: phosphatidylglycerol; PI: phosphatidylinositol; SQDG: sulphoquinovosyldiacylglycerol; TAG: triacylglycerol.

Figure 1

General biochemical composition of ω-3 (top) and ω-6 (bottom) PUFA.

Figure 2

Simplified diagram of the PUFA biosynthetic pathways occurring in the endoplasmic reticulum of microalgae. Enzymes that catalyse reactions in this pathway are mainly desaturases (DES) and elongases (ELO). On the left, saturated (SFA), monosaturated (MUFA), ω-6, and ω-3 polyunsaturated (PUFA) fatty acids are represented in yellow, pink, orange, and green, respectively. On the right panel, chemical structures of the most important fatty acids in this pathway are given.