Autotrophic vs. Heterotrophic Cultivation of the Marine Diatom Cyclotella cryptica for EPA Production

Abstract

Recently, the marketable value of ω-3 fatty acid, particularly eicosapentaenoic acid (EPA), increased considering their health effects for human consumption. Microalgae are considered a valuable and “green” source of EPA alternative to fish oils, but considerable efforts are necessary for their exploitation at an industrial level. Due to the high operation costs of photoautotrophic microalgae cultivation, heterotrophic growth represents a promising economic solution. Marine diatoms are the major ecological producers of ω-3 fatty acids. Few species of diatoms are capable to grow in the dark using organic carbon sources. The marine diatom Cyclotella cryptica was cultivated for 14 days under photoautotrophic and heterotrophic conditions to define the effects on growth parameters, lipid production, total fatty acids and EPA content. Photoautotrophic conditions led to a total EPA production of 1.6% of dry weight, 12.2 mg L−1 culture and productivity of 0.9 mg L−1 day−1. The heterotrophy cultures reported a total EPA production of 2.7% of dry cell weight, 18 mg L−1 culture, a productivity of 1.3 mg L−1 day−1, which are promising values in the prospective of improving culture parameters for the biotechnological exploitation of dark cultivation. C. cryptica could be a potential candidate for the heterotrophic production of EPA, also considering its robustness, capacity to resist to bacterial contaminations and plasticity of lipid metabolism.

Highly Valuable Polyunsaturated Fatty Acids from Microalgae: Strategies to Improve Their Yields and Their Potential Exploitation in Aquaculture

“…Some algal species, such as Galdieria sulphuraria, showed a higher PUFA content when cultured under heterotrophic rather than phototrophic conditions, where a higher content in saturated and monounsaturated FAs was observed [66]. Similar results were obtained with the marine diatom Cyclotella cryptica, in which heterotrophic conditions (i.e., culture media enriched with glucose) were found to be effective to increase the EPA yields with respect to the autotrophic regime [67]. Production of PUFAs under photoheterotrophic conditions can be also influenced by the carbon source: Under controlled (indoor) conditions, for example, the employment of glucose was found more effective than other organic substrates (fructose, sucrose, and maltose) to stimulate PUFAs' production in Tetraselmis gracilis and Platymonas convolutae [68].…”

Potential of Lipid Biosynthesis under Heterotrophy in the Marine Diatom Cyclotella cryptica

“…Growth Rate (μ) and Duplication Time (t d ) Calculation. Growth rate μ (expressed as divisions day −1 ) and doubling time t d (time required to achieve a doubling of the number of viable cells) were calculated in agreement with Cupo et al, 34 as follows:…”

“…26,33−35 Recently, we reported that the marine diatom Cyclotella cryptica is a promising source of EPA in the dark. 34 Here we investigate the effect of this condition on the total lipid composition and productivity by batch and repeated-batch processes. In order to test the potential of C. cryptica for future commercial applications, the study also estimates the quality of biodiesel produced from heterotrophic cultivation of the diatom.…”

“…Diatoms include over 200,000 estimated species, widely distributed in diverse natural habitats where they form large biomasses during seasonal blooms that sustain the aquatic food web and primary production on Earth. , Due to their resilience, metabolic plasticity, and capacity of accumulating lipids to a greater extent than other microalgae, diatoms have been often explored as biological platforms for the production of oil and valuable products. − However, studies related to heterotrophic cultivation are quite uncommon and mainly focus on the optimization for the production of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ,− …”

Advanced Applications for Protein and Compounds from Microalgae

“…Among lipids, long-chain polyunsaturated fatty acid (PUFA, ω-3) represent a major fraction of microalgae biomass such as Cyclotella cryptica , Nitzschia laevis , Navicula incerta , Navicula pelliculosa , and others [ 42 , 43 , 44 ]. Particularly, eicosapentaenoic acid (EPA 20:5) and docosahexaenoic acid (DHA 22:6) showed an interesting commercial potential [ 42 , 43 , 44 ]. Homologous overexpression and heterologous expression approaches have been investigated for an enhanced production of ω-3 species ( Table 1 ).…”