Testing for terrestrial and freshwater microalgae productivity under elevated CO₂ conditions and nutrient limitation

Area of Science:

• Biotechnology
• Phycology
• Sustainable Chemistry

Background:

• Microalgae are valuable biomass sources for fatty acids and carotenoids.
• Efficient CO2 capture by microalgae enhances valuable compound production.
• Understanding microalgae species and habitats for high CO2 productivity is crucial for the bioeconomy.

Purpose of the Study:

• To investigate the growth and productivity of diverse microalgae strains under elevated CO2 concentrations.
• To identify microalgae groups and habitats optimal for high CO2 conditions.
• To assess the impact of CO2 levels on biomass, chlorophyll, carotenoid, and fatty acid production.

Main Methods:

• Screened 81 defined microalgae strains for growth under 5-25% CO2 in air.
• Pre-selected strains for phylogenetic diversity and ambient CO2 productivity.
• Tested four new strains in liquid culture with varying macronutrient conditions (N and P starvation).

Main Results:

• Terrestrial green algae (Chlorophyceae, Trebouxiophyceae) showed enhanced growth up to 25% CO2.
• Unicellular red and stramenopile algae growth was suppressed above 5% CO2, with marine stramenopiles being particularly sensitive.
• Elevated CO2 (15%) increased biomass, chlorophyll, carotenoid, and fatty acid content, especially under nitrogen depletion.

Conclusions:

• Terrestrial green algae are promising for enhanced carotenoid and fatty acid production under elevated CO2.
• This finding enables economic and sustainable production of valuable compounds from microalgae.
• Utilizing industrial CO2 sources with these microalgae offers a sustainable bioeconomy solution.