Abstract
The importance of n-3 long chain polyunsaturated fatty acids (LC-PUFAs) for human health has received more focus the last decades, and the global consumption of n-3 LC-PUFA has increased. Seafood, the natural n-3 LC-PUFA source, is harvested beyond a sustainable capacity, and it is therefore imperative to develop alternative n-3 LC-PUFA sources for both eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3). Genera of algae such as Nannochloropsis, Schizochytrium, Isochrysis and Phaedactylum within the kingdom Chromista have received attention due to their ability to produce n-3 LC-PUFAs. Knowledge of LC-PUFA synthesis and its regulation in algae at the molecular level is fragmentary and represents a bottleneck for attempts to enhance the n-3 LC-PUFA levels for industrial production. In the present review, Phaeodactylum tricornutum has been used to exemplify the synthesis and compartmentalization of n-3 LC-PUFAs. Based on recent transcriptome data a co-expression network of 106 genes involved in lipid metabolism has been created. Together with recent molecular biological and metabolic studies, a model pathway for n-3 LC-PUFA synthesis in P. tricornutum has been proposed, and is compared to industrialized species of Chromista. Limitations of the n-3 LC-PUFA synthesis by enzymes such as thioesterases, elongases, acyl-CoA synthetases and acyltransferases are discussed and metabolic bottlenecks are hypothesized such as the supply of the acetyl-CoA and NADPH. A future industrialization will depend on optimization of chemical compositions and increased biomass production, which can be achieved by exploitation of the physiological potential, by selective breeding and by genetic engineering.
Highlights
Long chain polyunsaturated n-3 fatty acids (LC-PUFAs) are of increasing interest, due to their many positive effects for human health and their use as feed for fish farming
Even though genetic drivers are applicable for different approaches, we will in this review focus on the metabolic engineering approach because it has been discussed by Khozin-Goldberg et al (2011) as a strategy to obtain a high yield of n-3 LC-PUFA by microalgae and reviews focused on engineering of lipid metabolism in algae with emphasis on TAG accumulation [22,27,28,29,30]
It is important to identified genetic drivers for increased n-3 LC-PUFA synthesis as they can be used in different optimization approaches such as selective breeding, conditioning and metabolic engineering to enhance the n-3 LC-PUFA production in Chromista
Summary
Long chain polyunsaturated n-3 fatty acids (LC-PUFAs) are of increasing interest, due to their many positive effects for human health and their use as feed for fish farming. Even though genetic drivers are applicable for different approaches, we will in this review focus on the metabolic engineering approach because it has been discussed by Khozin-Goldberg et al (2011) as a strategy to obtain a high yield of n-3 LC-PUFA by microalgae and reviews focused on engineering of lipid metabolism in algae with emphasis on TAG accumulation [22,27,28,29,30]. Positive effects include anti-viral, anti-bacterial and anti-fungal effects [42,43] These benefits appear to be related to the alternations of fluidity in membrane phospholipids composition and function, gene expression and eicosanoid production [44]. A high percentage of n-3 FAs, e.g., >20%, is only found in marine organisms, and none of the marine organisms contain >15% n-6 FAs
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