Abstract
The influence of different nitrate concentrations in combination with three cultivation temperatures on the total fatty acids (TFA) and eicosapentaenoic acid (EPA) content of Nannochloropsis salina was investigated. This was done by virtue of turbidostatic controlled cultures. This control mode enables the cultivation of microalgae under defined conditions and, therefore, the influence of single parameters on the fatty acid synthesis of Nannochloropsis salina can be investigated. Generally, growth rates decreased under low nitrate concentrations. This effect was reinforced when cells were exposed to lower temperatures (from 26 °C down to 17 °C). Considering the cellular TFA concentration, nitrate provoked an increase of TFA under nitrate limitation up to 70% of the biological dry mass (BDM). In contrast to this finding, the EPA content decreased under low nitrate concentrations. Nevertheless, both TFA and EPA contents increased under a low culture temperature (17 °C) compared to moderate temperatures of 21 °C and 26 °C. In terms of biotechnological production, the growth rate has to be taken into account. Therefore, for both TFA and EPA production, a temperature of 17 °C and a nitrate concentration of 1800 μmol L−1 afforded the highest productivities. Temperatures of 21 °C and 26 °C in combination with 1800 μmol L−1 nitrate showed slightly lower TFA and EPA productivities.
Highlights
Microalgae are capable of synthesizing marine drugs, such as antioxidants, antibiotics, vitamins, and toxins, which are of growing interest for the cosmetic, pharmacological, and food industry [1,2,3]
This was done by virtue of both instrumental setup of the used photobioreactor [25] and turbidostatic control mode
As mentioned above the constancy of the biological dry mass (BDM) values indicated the reliability of the turbidostatic control mode and ensured that the measured effects at the end of the experiments could be assigned to the employed different nitrate concentrations and temperatures
Summary
Microalgae are capable of synthesizing marine drugs, such as antioxidants, antibiotics, vitamins, and toxins, which are of growing interest for the cosmetic, pharmacological, and food industry [1,2,3]. A further group of these marine drugs are fatty acids, a class of substances which can be synthesized and intracellularly accumulated in high amounts by microalgae [4,5,6,7] It has been widely discussed in recent years whether microalgae can be used for the production of biofuel and biodiesel [4,8,9,10,11]. The use of microalgae as a natural source of fatty acids for the aquaculture has become the focus of industrial and scientific developments [12,13,14] Such approaches prefer two different kinds of fatty acids. Whereas for biodiesel production microalgae with high contents of saturated (SFA) and monounsaturated (MUFA) fatty acids (the main components of the total fatty acids (TFA)) are sought [4], the content of polyunsaturated fatty acids (PUFA) is crucial for the use of microalgae in aquaculture [15,16]
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