Rubisco kinetic adaptations to extreme environments

Photosynthetic and chemosynthetic extremophiles have evolved adaptations to thrive in challenging environments by finely adjusting their metabolic pathways through evolutionary processes. A prime adaptation target to allow autotrophy in extreme conditions is the enzyme Rubisco, which plays a central role in the conversion of inorganic to organic carbon. Here, we present an extensive compilation of Rubisco kinetic traits from a wide range of species of bacteria, archaea, algae, and plants, sorted by phylogenetic group, Rubisco type, and extremophile type. Our results show that Rubisco kinetics for the few extremophile organisms reported up to date are placed at the margins of the enzyme's natural variability. Form ID Rubisco from thermoacidophile rhodophytes and form IB Rubisco from halophile terrestrial plants exhibit higher specificity and affinity for CO2 than their non-extremophilic counterparts, as well as higher carboxylation efficiency, whereas form ID Rubisco from psychrophile organisms possess lower affinity for O2. Additionally, form IB Rubisco from thermophile cyanobacteria shows enhanced CO2 specificity when compared to form IB non-extremophilic cyanobacteria. Overall, these findings highlight the unique characteristics of extremophile Rubisco enzymes and provide useful clues to guide next explorations aimed at finding more efficient Rubiscos. Autotrophic extremophiles exhibit unique physiological adaptations, which yielded great advances in basic and applied science. While the CO2-fixing enzyme Rubisco has been mainly characterized in non-extremophile organisms, the analysis of the few extremophile Rubisco kinetics reported up to date reveals variants placed at the enzyme's natural variability limits. This foundational knowledge supports future research, aiding photosynthesis genetic engineering and uncovering Earth's life origin.