Metabolic modeling suggested noncanonical algal carbon concentrating mechanism in <i>Cyanidioschyzon merolae</i>

Extremophilic organisms are fascinating due to their unique biology, which makes them valuable as functional model organisms and potential candidates for biotechnology applications. Cyanidioschyzon merolae is an extremophilic red microalga and one of the few organisms that rely on photosynthesis in high-temperature environments, where hot and acidic conditions limit the availability of inorganic carbon and challenge biological carbon fixation. Green algae grow in challenging environments by using a carbonconcentrating mechanism (CCM) involving a specialized pyrenoid structure. CCMs enhance photosynthetic efficiency by concentrating CO 2 around rubisco, providing adequate substrate for carbon fixation and inhibiting the competing oxygen-fixation reaction of rubisco (Miyagishima et al., 2021). Unlike green algae, the ability of the red algae C. merolae to assimilate CO 2 efficiently is not well-characterized and the presence and operation of its CCM is not unequivocal. For example, it lacks the anatomical structures associated with pyrenoid CCM organelles and cannot take up external bicarbonate. In such cases where biochemical knowledge is limited, mathematical and computational surrogate modeling approaches can help to understand possible cellular and molecular mechanisms in organisms and how they survive extreme environmental