Metabolic relationships between macro- and micronutrients, and the eicosapentaenoic acid and docosahexaenoic acid contents of Pavlova lutheri

Abstract

The use of specific microalgae as sources of polyunsaturated fatty acids (PUFA), for incorporation in either aquaculture or human diets, has been receiving increasing interest. The fatty acid profile of intracellular fats in a given species can, within certain limits, be modulated via manipulation of the culture growth conditions, namely nutrient availability. In attempts to shed further light on the effects of chemical parameters upon microalgal metabolism, correlations between the components of a medium and the resulting biomass yield, as well as the eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents are presented, using Pavlova lutheri as model system. Although several studies of individual nutrients have been published previously, the effects of variation of all medium components upon fatty acid production are systematically presented here, apparently for the first time.The optimum formulation to optimise EPA and DHA contents should consider the buffering agent, since some of them are toxic to the cells; P. lutheri was able to use several nitrogen sources, yielding equivalent amounts of EPA and DHA; synthesis of EPA was induced in culture media under low salinity, whereas a trend could be noticed between decreasing yields of EPA and increasing concentrations of N, at 0.15 g L −1 of P. Regarding the micronutrient composition, a culture medium lacking sulphur was unable to sustain cellular growth, whereas cultures deprived of either calcium, iron or manganese revealed a statistically significant decrease in cellular yields relative to those possessing such minerals; conversely, those cultures without boron produced higher cell numbers than those containing this element. Media deprived of boron, molybdenum or copper led to increases of the relative amounts of both EPA and DHA, whereas calcium deficiency decreased the levels of those PUFA.

Selection of Direct Transesterification as the Preferred Method for Assay of Fatty Acid Content of Microalgae

“…The majority of previously reported DT protocols for microalgae used lyophilised biomass and a single acid catalyst [25][26][27][28][29][30][31]. This study has shown that drying of centrifuged algal biomass was not necessary if a sequential combination of basic and acid catalysts were used.…”

“…Diverse methods have been used for DT, but most involve the addition of an organic solvent, methanol, catalyst and heat to a small amount of dried sample (see [21] and [22] for comprehensive reviews of this). DT has previously, although infrequently, been applied to the quantification of fatty acids in microalgae [24][25][26][27][28][29][30][31], however, no evaluation or comparison to alternative methods has been made.…”

Iron and copper limitations differently affect growth rates and photosynthetic and physiological parameters of the marine diatom Pseudo‐nitzschia delicatissima

“…Mildly limited cells (10Fe and 0Cu), on the contrary, could increase the ratio of lipid production over esterase activity up to 11.9 3 10 23 6 1.0 3 10 23 AU AU 21 , with a production rate as high as 134 AU cell 21 d 21 . Carvalho et al (2006) also showed that Cu-limited cultures of Pavlova lutheri exhibited an increase of their lipid content. Because growth is reduced, while photosynthesis does not seem to be affected, Cu-starved cultures may have extra energy to store in lipid form.…”

Genetic algorithm for the medium optimization of the microalga Nannochloropsis gaditana cultured to aquaculture

“…The ease of cultivation, lack of toxicity and high nutritional value (proteins, vitamins and polyunsaturated fatty acids) are some of the requirements that microalgae must achieve to be used in aquaculture (Hemaiswarya et al, 2010). (Carvalho et al, 2006). Several studies have also demonstrated that the optimization of the culture medium composition, including the trace component, heavy metals and vitamins, are essential in the growth of Nannochloropsis sp.…”