In Metabolic Engineering of Eukaryotic Microalgae: Potential and Challenges Come with Great Diversity

Abstract

The great phylogenetic diversity of microalgae is corresponded by a wide arrange of interesting and useful metabolites. Nonetheless metabolic engineering in microalgae has been limited, since specific transformation tools must be developed for each species for either the nuclear or chloroplast genomes. Microalgae as production platforms for metabolites offer several advantages over plants and other microorganisms, like the ability of GMO containment and reduced costs in culture media, respectively. Currently, microalgae have proved particularly well suited for the commercial production of omega-3 fatty acids and carotenoids. Therefore most metabolic engineering strategies have been developed for these metabolites. Microalgal biofuels have also drawn great attention recently, resulting in efforts for improving the production of hydrogen and photosynthates, particularly triacylglycerides. Metabolic pathways of microalgae have also been manipulated in order to improve photosynthetic growth under specific conditions and for achieving trophic conversion. Although these pathways are not strictly related to secondary metabolites, the synthetic biology approaches could potentially be translated to this field and will also be discussed.

Long-duration effect of multi-factor stresses on the cellular biochemistry, oil-yielding performance and morphology of Nannochloropsis oculata

“…There has been progress in increasing the lipid biosynthesis capability of microalgae through high biomass cultivation, metabolic engineering and genetic engineering [6–8]. To increase fatty acid (FA) biosynthesis, genetic engineering regulating cell metabolic pathways is feasible, including the over-expression or inhibition of certain rate-limiting enzymes [7–9], the comprehensive regulation of lipid biosynthesis by transcription factors [10], the construction of genes in association with spontaneous secretion of FA and the construction of efficient expression vectors for exogenous genes [3].…”

“…Metabolic pathway regulation, however, is relatively easy to undertake, the nature of which is to expose microalgae to environmental stresses, thus resulting in cellular metabolic flux with a shift to lipid biosynthesis [3, 6]. Microalgae have evolved countermeasures for survival in the face of various environmental adversities [6, 11].…”

“…Microalgae have evolved countermeasures for survival in the face of various environmental adversities [6, 11]. The adaptation generated can quickly become evident as variations in their growth, physiology, biochemistry and morphology.…”

“…The adaptation generated can quickly become evident as variations in their growth, physiology, biochemistry and morphology. However, high diversity of microalgae may well lead to the differences in cellular metabolic pathways and metabolic regulation between different species [6, 12, 13]. It is therefore possible to regulate many physiological metabolic processes in microalgae by changing their culture conditions, to obtain the end products or intermediate products of algal cells, such as proteins, FAs, pigments and polysaccharides.…”

Cyanobacteria: Promising biocatalysts for sustainable chemical production

“…Cyanobacteria are also readily genetically tractable which provides ease of genetic manipulations to alter their metabolism. In contrast, the genetic complexity of eukaryotic algae has made metabolic engineering more challenging (11). Importantly, cyanobacteria can be cultivated in bioreactors in arid or otherwise unfarmable land which minimizes the competition with food crops (12).…”