Recent progress in genetically modified microalgae for enhanced carbon dioxide sequestration

Reducing carbon dioxide (CO2) emissions has been a hot research topic in recent years. The integration of microalgae cultivation using CO2 from power plants and factories has been introduced as an environmentally friendly approach. However, strains with high biomass productivity are required to achieve a sustainable integrated platform. Improving photosynthesis is critical to increase both biomass productivity and CO2 sequestration efficiency. The improvement of photosynthesis is often attained by enhancing the efficiency of enzymes that are involved in CO2 fixation, reducing the antenna size to avoid energy loss, extending the photosynthetically active radiation range to broaden the light utilization capacity, increasing CO2 assimilation by replacing the existing carbon fixation pathway with more efficient pathways and enzymes, and reducing the release of captured CO2. Implementation of these modifications is achievable via transformation and gene editing. The transformation of the new gene constructs into microalgae has been discussed as an extremely challenging task in the past decade. In recent studies, the digestion of the microalgae cell wall, as one of the main barriers of transformation, has been recommended as a promising approach. Moreover, the emergence of preassembled Cas9 protein-gRNA ribonucleoproteins that do not require vector constructs has been suggested as an efficient approach for gene editing. This review comprehensively describes the potential strategies that enhance microalgae CO2 fixation, provides insight into current limitations and gaps, and proposes future perspectives.