Biotechnological screening of microalgal strains
Biotechnological screening of microalgal strains for biomass production and utilization
The cultivation of microalgae is carried out in 400 ml glass tubes, 2 l bottles and 4000 l basins. A continuous gassing with air or a mixture of air and CO2 ensures a good mixing of the culture.
Microalgae represent an enormous natural resource to generate a large number of substances. They can have pharmacological activity, be used as additives in food, feed and cosmetics or can be used for bioenergy production. The variety of potential agents and the use of microalgae biomass for the production of these substances are little investigated and not exploited for the existing market. Because of the enormous biodiversity of microalgae, they show great promise for new products.
A large number of microalgae strains of the Culture Collection of Algae at Göttingen University (SAG) and research projects associated with this collection are investigated within the presented project of the Centre of Excellence of Biomass (CE Biomass) in Schleswig-Holstein.
Aims of the project
In this study, a broad range of microalgae strains of SAG was screened in collaborations with various academic and industrial partners for following parameters:
• Optimization of culturing conditions and biomass production
• Total fat content (for biodiesel production)
• Fatty acid composition (for food and feed)
• Antioxidants (eg. carotinoids and tocopherol (Vitamin E))
• Carbon dioxide absorption capacity
• Biogas yield test (biogas plants)
• Compounds with antibacterial effect
• Hydrogenase activities (for biohydrogen production)
• Pharmaceutical and cosmetic products
Results and discussion
Total fat content and fatty acid composition
The total fat content gives information about the usability of microalgal biomass in the production of biodiesel. Microalgae are also able to synthesize polyunsaturated fatty acids (PUFA). Therefore, microalgal fatty acids have a very promising biotechnological market for food, feed and biodiesel. In our investigation total fat content up to 70% of dry weight and several different fatty acids could be identified.
Biogas yield test
Because of its high biomass productivity microalgae could play an important role for production of biogas. Microalgae biomass could be interesting for biogas production when high priced products could be extracted from algae cells initially and then the remains of biomass could also be used in biogas plants again. In our analysis microalgae show a specific gas yield up to 520 ml N/g VS.
Carbon dioxide absorption capacity
Microalgae possess high CO2 fixation capacities and under optimal culture condition express growth rates several orders of magnitudes higher than conventional crop plants (Chisti, 2007; Chisti, 2008). Carbon dioxide emitted during industrial processes has been used to gas bioreactors, in which microalgae produced biomass from CO2 via photosynthesis. With the biological approach, CO2 is converted into algal biomass that provides a broad range of valuable compounds used in pharmacy, cosmetic, food and feed supplements as well as for bioenergy production.
Here, we investigated the effects of different CO2 concentrations on algal strains for biomass production, tocopherol content, fatty acid composition and total fatty acid content. The overall aim was to elucidate the CO2 absorption capacity of the investigated strains and if they are suitable for cultivation at high CO2 concentrations. The highest CO2 concentration employed in this study was 15 % (v/v), as this resembles the concentration of CO2 in most flue gases (Maeda et al., 1995; Borodyanski et al., 2011).
It was observed that some microalgae are able to grow at 15 %. CO2. In contrast, the growth of some microalgae was completely inhibited at this concentration. Interestingly, the concentration of CO2 influenced not only the biomass production but also the α-tocopherol content, the fatty acid composition and the fatty acid content.
Tocopherol (Vitamin E) content
Tocopherols are a group of four (α, β, γ, and δ) lipid-soluble antioxidants synthesized only in photoautotrophy organisms (Gómez-Coronado et al., 2004; Munne-Bosch and Alegre, 2002) and animal cells are unable to synthesize them so they must obtain them from plant sources (Vismara et al., 2003). α-tocopherol is the most abundant form and has the most important role in vitamin E activity of all tocopherols. α-tocopherol has a major role in the prevention of light-induced pathologies of skin and eyes (Chiu and Kimball, 2003). The functions such as anti-tumor, anti-aging, and cholesterol lowering of tocopherols can also be attributed to the antioxidization functions (Bramley et al. 2000).
Our result showed that the content of α-tocopherol increased in the stationary phase compared to the logarithmic phase. We also observed that the α-tocopherol content increased when low NO3- concentrations are employed. The α-tocopherol content was low when the concentration of CO2 in the aeration gas was high.
The result of the current study showed that microalgae are able to generate a large number of substances in different quantities. In addition, between closely related species and even among multiple isolates of the same species, the productivities may be rather variable. With enormous biodiversity, microalgae show great promise for new products.
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