Abstract
With the depletion of global fish stocks, caused by high demand and effective fishing techniques, alternative sources for long chain omega-3 fatty acids are required for human nutrition and aquaculture feeds. Recent research has focused on land-based cultivation of microalgae, the primary producers of omega-3 fatty acids in the marine food web. The effect of salinity on fatty acids and related gene expression was studied in the model marine microalga, Tetraselmis sp. M8. Correlations were found for specific fatty acid biosynthesis and gene expression according to salinity and the growth phase. Low salinity was found to increase the conversion of C18:4 stearidonic acid (SDA) to C20:4 eicosatetraenoic acid (ETA), correlating with increased transcript abundance of the Δ-6-elongase-encoding gene in salinities of 5 and 10 ppt compared to higher salinity levels. The expression of the gene encoding β-ketoacyl-coenzyme was also found to increase at lower salinities during the nutrient deprivation phase (Day 4), but decreased with further nutrient stress. Nutrient deprivation also triggered fatty acids synthesis at all salinities, and C20:5 eicosapentaenoic acid (EPA) increased relative to total fatty acids, with nutrient starvation achieving a maximum of 7% EPA at Day 6 at a salinity of 40 ppt.
Highlights
Long-chain polyunsaturated fatty acids (LC-PUFA), such as eicosapentaenoic acid (EPA), eicosatetraenoic acid (ETA) and docosahexaenoic acid (DHA), which are omega-3 fatty acids, and arachidonic acid (ARA), an omega-6 fatty acid, provide significant health benefits, including a reduced risk of hypertension, cardiac arrhythmia, myocardial infarction and thrombosis [1]
Nutrient consumptions, fatty acid profiling and expression differences for genes involved in FA synthesis were profiled over six days after the initial culture inoculation to determine the effect of salinity
In Tetraselmis sp., we found an increase in Beta-Keto acyl synthase (BKAS) and ACSase transcript abundance with nutrient depletion, but there was no significant difference in gene expression between salinities and no differences in the proportion of FA carbon chain length or the level of desaturation
Summary
Long-chain polyunsaturated fatty acids (LC-PUFA), such as eicosapentaenoic acid (EPA), eicosatetraenoic acid (ETA) and docosahexaenoic acid (DHA), which are omega-3 fatty acids, and arachidonic acid (ARA), an omega-6 fatty acid, provide significant health benefits, including a reduced risk of hypertension, cardiac arrhythmia, myocardial infarction and thrombosis [1]. Interest on the sustainability of the omega-3 sources has moved efforts towards land-based production, including farmed fish, genetically modified plants, regulated krill catches and large-scale production of microalgae [4]. Microalgae are considered a viable and sustainable source of LC-PUFA, including omega-3 fatty acids. They have important advantages for commercial production over transgenic plants or fungi [5], including high areal productivity. The response to environmental stress of an altered salinity can lead to the cessation or slowing of algal growth and biomass accumulation, shifting photosynthetic energy towards the accumulation of chemical energy in the form of fatty acids (FA) or starch [10,15,16,17]. It is essential to investigate the effect of salinity on algal growth and omega-3 production in microalgal strains with commercial potential
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