CAH1 and CAH2 as key enzymes required for high bicarbonate tolerance of a novel microalga Dunaliella salina HTBS

• An extremely alkalihalophilic microalgae Dunaliella salina HTBS was isolated.
• The presence of extracellular CAs (CAH1 and CAH2) in HTBS was confirmed.
• CAH1 and CAH2 played a multifunctional role for tolerating high HCO3− concentration.
• HTBS featured with tolerance of 70 g L−1 NaHCO3, 30% CO2 and low temperature (7 °C)

Outdoor microalgal cultivation with high concentration bicarbonate has been considered as a strategy for reducing contamination and improving carbon supply efficiency. The mechanism responsible for algae's strong tolerance to high bicarbonate however, remains not clear. In this study, we isolated and characterized a strain and revealed its high bicarbonate tolerant mechanism by analyzing carbonic anhydrase (CA). The strain was identified as Dunaliella salina HTBS with broad temperature adaptability (7–30 °C). The strain grew well under 30% CO2 or 70 g L−1 NaHCO3. In comparison, two periplasm CAs (CAH1 and CAH2) were detected with immunoblotting analysis in HTBS but not in a non-HCO3−—tolerant strain. The finding was also verified by an enzyme inhibition assay in which only HTBS showed significant inhibition by extracellular CA inhibitor. Thus, we inferred that the extracellular CAH1 and CAH2 played a multifunctional role in the toleration of high bicarbonate by HTBS.