Enhanced Lipid Production and Molecular Dynamics under Salinity Stress in Green Microalga Chlamydomonas reinhardtii (137C)

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.

Lipid accumulation patterns and role of different fatty acid types towards mitigating salinity fluctuations in Chlorella vulgaris

“…Due to the diverse phylogeny of microalgae, significant differences do occur in the types of fatty acids partitioned into TAG upon reception of salinity stress. For example, it was observed that Chlorophyta tended to synthesises saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) while Ochrophyta (diatoms) preferred production of polyunsaturated fatty acids (PUFA) when stressed 5 . However, regardless of phylogeny, oleaginous microalgae will rearrange its lipid pathways in order to accumulate high amounts of TAG (about 40–70% per dry weight) upon exposure to abiotic stress conditions 4 , 6 .…”

Systematic hormone-metabolite network provides insights of high salinity tolerance in Pongamia pinnata (L.) pierre

“…Increased accumulation of saturated fatty acids might protect the membrane fluidity to protect the cell and cellular organelle from Na + toxicity and ion leakage (Shu et al, 2015;Atikij et al, 2019). Our results also showed an increase in coumarate and benzoate in both leaves and roots, while significant increase was observed in caffieate and ferulate levels only in roots of salt treated plants.…”

An appraisal of the variable response of microalgal lipids to culture salinity

“…In freshwater microalgae, changes in 16:0 and 18:0 with salt concentration are also variable. In C. reinhardtii, high salt conditions resulted in 16:0 depletion and 18:0 enrichment, 141 but also in enrichment 99,128 and minor changes in both FA. 174 16:0 and 18:0 changed little in Chlamydomonas mexicana over the 0-100 mM NaCl range, 175 and sea ice Chlamydomonas sp.…”

“…Most of this genomic information is based on genome predictions of orthologous genes in seed plants and is pending experimental verification. 127 Under increased NaCl concentration, TG biosynthesis genes were downregulated in N. oleabundus, 73 Chlamydomonas reinhardtii 128 and P. kessleri. 75 In C. zofingiensis, only one in ten diacylglycerol acyltransferase (DGAT) genes was upregulated by salt stress.…”

“…Minor changes in 14:0 with salt stress were reported in the freshwater chlorophytes Botryococcus braunii 173 and C. reindhartii. 128 On the other hand, high salt stress affected 14:0 in Desmodesmus abundans 103 and Scenedesmus sp. 2 It seems plausible that 14:0 is not needed in storage lipids or as SFA to decrease membrane fluidity in those microalgae that degrade this SFA under salt stress.…”