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

This study investigated the possible adaptation of a microalgae consortium to elevated carbon dioxide (CO₂) 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 CO₂ supplementation, from 1.327 d^-1 in the initial culture without CO₂ supplementation to 0.369 d^-1 at 50 % CO₂. At the lowest applied CO₂ supplementation of 10%, the growth rate was 0.735 d^-1. Interestingly, supplementation of 40% CO₂ in the final run showed insignificant difference in the growth rate of the consortium compared to that at 10% CO₂. 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 CO₂ enrichment. Compared to the initial consortium, the proportion of polyunsaturated fatty acids (PUFAs) increased from 36.2% to 58.1% under 40% CO₂, 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% CO₂ 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 CO₂ 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.