Exploring the performance and mechanisms of Mychonastes rotundus in fixing CO2 based on multi-omics analysis

Utilizing microalgae to immobilize carbon dioxide (CO2) was regarded as one of the most environmentally friendly, safe and sustainable carbon capture, utilization and storage technologies. Mychonastes rotundus was a freshwater algae belonging to the Chlorophyceae. It had a wide range of habitats around the world, especially growing in streams and large stagnant water bodies. Mychonastes rotundus contained high levels of lipids and proteins, and could utilize various molecular forms of nutrients and light wavelengths for photosynthesis. However, the application of Mychonastes rotundus for carbon sequestration was rarely reported. In this study, CO2 fixation efficiency and the physiological characteristics of Mychonastes rotundus at different CO2 input concentrations (10%, 20% and 30%) were investigated, and its transcriptomics and metabolomics were reported for the first time. The results showed that Mychonastes rotundus achieved the highest and stablest carbon fixation efficiency and its cell hydrophobicity was the strongest at 20% CO2. Compared with that without CO2 input, Mychonastes rotundus upregulated 21444 genes and 188 metabolites, and genes encoding EC: 3.1.3.37 and EC: 1.2.1.13 in carbon fixation pathways upregulated. The most significant enrichment pathways were metabolic pathways and ABC transporters to resist cell damage caused by CO2. However, the protein synthesis and material exchange between nucleus and cytoplasm were inhibited and ATPase activity decreased to 50% at 30% CO2 concentration, leading to massive death of microalgae cells. This study provided a wide range of mechanistic insights into the CO2 fixation process of Mychonastes rotundus at the genetic level.