Abstract
Microalgal lipids are a source of valuable nutritional ingredients in biotechnological industries, and are precursors to biodiesel production. Here, the effects of salt-induced stresses, including NaCl, KCl, and LiCl stresses, on the production of lipid in green microalga Chlamydomonas reinhardtii (137c) were investigated. NaCl stress dramatically increased saturated fatty acids (SFAs), which accounted for 70.2% of the fatty acid methyl ester (FAMEs) under stress. In contrary, KCl stress led to a slight increase in SFAs (47.05%) with the remaining being polyunsaturated fatty acids (PUFAs) (45.77%). RT-PCR analysis revealed that the genes involved in FA biosynthesis, such as PDH2, ACCase, MAT and KAS2, were up-regulated by NaCl-induced stress. Conversely, the genes responsible for the Kennedy pathway were suppressed. The alteration of FA homeostasis was further assessed by overexpressing MAT, the enzyme responsible for the production of malonyl-ACP, a key building block for FA biosynthesis, in the cyanobacterium Synechococcus elongatus PCC 7942. Intracellular FA composition was affected, with a predominant synthesis of SFAs in transformed cells. Owing to the diversity and relative abundance of SFAs, monounsaturated fatty acid (MUFAs) and PUFAs enable the feasibility of using microorganisms as a source of microalgal lipids or valuable nutritional ingredients; salt-induced stress and expression of MAT are useful in providing precursors for enhanced lipid production.
Highlights
Microalgae are a group of plant-like, unicellular photosynthetic organisms with ubiquitous distribution
Given the expansive diversity of microalgae in nature, a diverse assortment of fatty acids (FAs) and lipid classes of nutritional importance are biosynthesized in microalgae
Our results demonstrated that NaCl and KCl, but not LiCl or sodium acetate, triggered palmelloid formation (Figure 1), suggesting that NaCl and KCl influenced the expression of gene(s) involved in palmelloid formations or polysaccharide metabolism, such as biofilm production
Summary
Microalgae are a group of plant-like, unicellular photosynthetic organisms with ubiquitous distribution. Given the expansive diversity of microalgae in nature, a diverse assortment of fatty acids (FAs) and lipid classes of nutritional importance are biosynthesized in microalgae. FA and lipid compositions vary substantially among phylogenetic groups [1,2]. Green microalgae predominantly accumulate SFAs and MUFAs, together with trace amounts of. Mar. Drugs 2019, 17, 484; doi:10.3390/md17080484 www.mdpi.com/journal/marinedrugs.
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