Enhanced carbon capture and storage in the green microalga Chlamydomonas by heterologous expression of an engineered carbonic anhydrase.

Microalgae are regarded as a promising platform for carbon capture and storage (CCS). A key target for enhancing CCS in microalgae is the carbon-concentrating mechanism (CCM), which is heavily reliant on carbonic anhydrase (CA) activity. Overexpressing CA in microalgae may offer an effective approach to capture excess CO2. A directed-evolution-generated variant of Desulfovibrio vulgarisCA (DvCA) with ultrastable properties and efficient carbon capture capability in vitro was previously reported. Here, the DvCA was heterologously expressed in the green alga Chlamydomonas reinhardtii (Chlamydomonas). The engineered Chlamydomonas strain, expressing the DvCA in the chloroplast, exhibited significantly higher inorganic carbon uptake, total carbon conversion efficiency and more biomass than parental line (PL). Under photoautotrophic conditions (ambient CO2), photosynthetic rate and photoprotection were also enhanced in DvCA expressing transformants. Moreover, the DvCA transformants showed a significant increase in carbon storage, with starch and triacylglycerol (TAG) content rising by 25 % and 53 %. In addition, the expression levels of major genes directly involved in photosynthesis, TAG and starch biosynthesis were upregulated in DvCA transformants comparted to PL. These results demonstrated that heterologous expression of highly stable CA is an effective strategy for optimizing microalgal CCMs, offering considerable promise for enhancing CCS using microalgae.