Examining the impact of carbon dioxide levels and modulation of resulting hydrogen peroxide in Chlorella vulgaris
Chien‐Ting Li, Kevin Trigani, Cristal Zúñiga, Richard Eng, Elizabeth Chen, Karsten Zengler, Michael J. Betenbaugh
Abstract
The eukaryotic green alga Chlorella vulgaris UTEX 395 was cultured under carbon dioxide (CO 2 ) concentrations ranging from 0.04% to 15% in order to examine the effect of CO 2 on algal growth, biomass composition and reactive oxygen species (ROS) accumulation in the culture medium. Supplying 5% CO 2 yielded the highest biomass growth rate (μ = 0.35 day −1 ) compared with 0.04% (μ = 0.15 day −1 ) and 15% (μ = 0.19 day −1 ) CO 2 conditions. Experimental evidence showed that increasing CO 2 levels from 0.04% to 2% and above did not alter overall protein content significantly but did enhance C16:1 and C18:1 monounsaturated fatty acid (MUFA) composition by 3.5 and 2 fold, respectively, reducing C18:3 polyunsaturated fatty acid (PUFA) levels. Interestingly, bubbling 5% and 15% CO 2 increased one type of ROS, H 2 O 2 levels, in sterile medium by 1.8 to 2 μM while growing C. vulgaris substantially lowered these H 2 O 2 levels. The ability to lower H 2 O 2 levels, which was reduced for non-viable algal cells, was also observed with C. protothecoides UTEX 29 and C. sorokiniana UTEX 1230. In order to understand the impact of H 2 O 2 directly, 10 μM and 25 μM H 2 O 2 were added daily to 0.04% CO 2 -bubbled C. vulgaris cultures. Periodic H 2 O 2 addition did not affect the growth of C. vulgaris or change its biomass composition. These findings demonstrate C. vulgaris can thrive at elevated concentrations of CO 2 and also showed the capacity of microalgae to reduce the ROS level, specifically H 2 O 2 , present in a CO 2 bubbling environment.