Progressive adaptation of microalgae consortium to elevated carbon dioxide coupled with enhanced production of essential fatty acids

• Microalgae consortium was adapted to CO 2 levels up to 50%. • Growth rate decreased by increasing CO 2 rises, stabilizing at 40% compared to 10% CO 2 . • CO 2 enrichment shifts microbial community, favoring growth-promoting bacterial. • Essential fatty acids (EFAs) increased from 36.2% to 58.1% under 40% CO 2 . • Adaptation to high CO 2 improves EFAs production, aiding sustainability and industry. This study investigated the possible adaptation of a microalgae consortium to elevated carbon dioxide (CO 2 ) concentrations reaching up to 50 % v/v in a lab-scale photobioreactor (PBR). Results showed a significant reduction in the growth rate of the consortium with increasing CO 2 supplementation, from 1.327 d -1 in the initial culture without CO 2 supplementation to 0.369 d -1 at 50 % CO 2 . At the lowest applied CO 2 supplementation of 10%, the growth rate was 0.735 d -1 . Interestingly, supplementation of 40% CO 2 in the final run showed insignificant difference in the growth rate of the consortium compared to that at 10% CO 2 . Microbial community analysis revealed a shift towards bacterial genera that enhance the microalgal growth, while some algal genera (mainly Tetradesmus and Chlorella ) became more dominant under CO 2 enrichment. Compared to the initial consortium, the proportion of polyunsaturated fatty acids (PUFAs) increased from 36.2% to 58.1% under 40% CO 2 , mainly due to the increase in the proportion of essential fatty acids (EFAs) such as alpha-linolenic acid (ALA) and linoleic acid (LA). Under 40% CO 2 supplementation, an increase in cell size was observed, despite a reduction in cell number. This study highlights the potential of microalgae consortia to adapt to high CO 2 levels, leading to a dominance of certain algal genera. This adaptation improves the production of EFAs, thereby contributing to both environmental sustainability and industrial applications.