Isolation and characterization of high-CO2 sensitive Nannochloropsis salina mutant

Carbon acquisition and utilization are fundamental processes required for the growth and metabolism of algae, eukaryotic organisms that play a crucial role in global carbon cycling and contribute to the primary productivity of aquatic ecosystems. Algal cells rely on carbonic anhydrases (CAs) to facilitate the acquisition of inorganic carbon (Ci) and its conversion into bicarbonate ions (HCO 3 − ) for various cellular processes. Understanding the molecular mechanisms that underlie Ci regulation is vital for unraveling the adaptation of algae to different CO 2 conditions and enhancing the production of algal biomass. In this study, we characterized mutant algae showing robust growth under low CO 2 conditions but impaired growth in high CO 2 environments. Our investigation revealed a significant reduction in intracellular Ci content in the mutant, suggesting a disruption in Ci regulatory mechanisms. Through molecular analysis, we identified the pKIWI502 gene homolog as one of the mutated loci, which played a critical role in Ci regulation and was responsible for the mutant phenotype. Introduction of the intact pKIWI502 gene into mutant algae resulted in the recovery of high-CO 2 sensitivity and the restoration of intracellular Ci content. These findings highlight the possible role of the pKIWI502 homolog in pH homeostasis and Ci regulation, and provide insights into the molecular basis of the mutant phenotype. Furthermore, our study improves the understanding of algal physiology and offers potential strategies for enhancing algal biomass production and carbon capture technologies.