CO2 TOLERANCE IN SAXITOXIN-PRODUCING AND NON-PRODUCING RAPHIDIOPSIS RACIBORSKII

Abstract

Rising carbon dioxide (CO2) levels due to human activities have potential impacts on aquatic ecosystems. To explore the physiological and transcriptomic response of Raphidiopsis raciborskii (cyanobacteria) to an extremely high CO2 environment, we investigated the effects of a high pCO2 (40,000 ppm) concentration on the growth, photosynthesis, and saxitoxin production of the toxic and nontoxic strains, identifying any associated transcriptomic changes. Our study found that R. raciborskii was able to cope with extremely elevated CO2 levels regardless of toxin production, with physiological parameters remaining unaffected. However, transcripts related to bicarbonate transporters and the RuBisCO enzyme indicate the upregulation of carbon concentrating mechanisms (CCMs) and downregulation of the Calvin cycle, respectively. These findings suggest that R. raciborskii has the potential to cope with carbon dioxide in water above predicted levels. Our study is significant in the context of the variable CO2 scenario up until present conditions, particularly for early evolved photosynthetic groups, like cyanobacteria. The study highlights the role of RuBisCO enzymes and CCMs in carbon dioxide fixation and the possible impacts of rising CO2 levels due to human activities on aquatic ecosystems.