Abstract
Microalgal biotechnology has gained considerable importance in recent decades. Applications range from simple biomass production for food and animal feed to valuable products for fuel, pharmaceuticals, health, biomolecules and materials relevant to nanotechnology. There are few reports of the exploration of wider microalgae biodiversity in the literature on high value microalgal compounds, however, because it is believed that there is little to be gained in terms of biomass productivity by examining new strains. Still, without diversity, innovation in biotechnology applications is currently limited. Using microalgal diversity is a very promising way to match species and processes for a specific biotechnological application. In this context, three benthic marine diatom strains (Entomoneis paludosa NCC18.2, Nitzschia alexandrina NCC33, and Staurosira sp NCC182) were selected for their lipid production and growth capacities. Using PAM fluorometry and FTIR spectroscopy, this study investigated the impact of nitrogen repletion and depletion as well as light intensity (30, 100, and 400 μmol.photons.m-2.s-1) on their growth, photosynthetic performance and macromolecular content, with the aim of improving the quality of their lipid composition. Results suggest that under high light and nitrogen limitation, the photosynthetic machinery is negatively impacted, leading cells to reduce their growth and accumulate lipids and/or carbohydrates. However, increasing lipid content under stressful conditions does not increase the production of lipids of interest: PUFA, ARA and EPA production decreases. Culture conditions to optimize production of such fatty acids in these three original strains led to a balance between economic and ecophysiological constraints: low light and no nitrogen limitation led to better photosynthetic capacities associated with energy savings, and hence a more profitable approach.
Highlights
Production of microalgae is gaining interest for the supply of biofuels, feedstock and for added value compounds; several thousand species of microalgae have been screened for lipid production, including diatoms [1,2,3,4,5,6,7,8]
For Staurosira sp., under N+ conditions, the same amount of nitrogen was consumed in Low light (LL), High light (HL), and Middle light (ML) (p = 0.30); as for the two other species, nitrogen consumption was higher in N+ than in N- (p < 0.05)
For E. paludosa, as for nitrogen, more phosphate was consumed in N+ conditions under HL and ML than under LL (p < 0.001)
Summary
Production of microalgae is gaining interest for the supply of biofuels, feedstock and for added value compounds; several thousand species of microalgae have been screened for lipid production, including diatoms [1,2,3,4,5,6,7,8]. The most studied molecules are eicosapentaenoic acid (EPA) and arachidonic acid (ARA), which belong to the polyunsaturated fatty acids (PUFA). Fatty acids such as EPA and ARA are considered pharmacologically important for dietetics and therapeutics. They have been used for prophylactic and therapeutic treatment of chronic inflammations (e.g. rheumatism, skin diseases, and inflammation of the mucosa of the gastrointestinal tract) [9]. Nutrient stress, e.g., nitrogen deprivation, phosphorus starvation, or iron supplementation can enhance the lipid content in many microalgae species [23,24,25,26]. Lipid biosynthesis varies within the different diatom species, their growth stages and the environmental parameters [27,28]
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