Enhanced carbon capture and utilization (CCU) using heterologous carbonic anhydrase in Chlamydomonas reinhardtii for lutein and lipid production

Abstract

Chlamydomonas reinhardtii is a model microalga that has a higher growth rate and produces high levels of lutein and lipids, but biomass production is limited. Carbonic anhydrase (CA) converts atmospheric CO2 to bicarbonate which is crucial for carbon‐concentrating mechanism (CCM) in microalgae and boosts cell density. Therefore, C. reinhardtii harboring the heterologous CA from Mesorhizobium loti (MlCA) and Sulfurihydrogenibium yellowstonense (SyCA) were explored to increase CO2 capture and utilization (CCU) through different culture devices. Genetically modified C. reinhardtii was able to grow from mixotrophic to autotrophic conditions. Subsequently, biomass, lutein, and lipid were maximized to OD680 of 4.56, 21.32 mg/L and 672 mg/L using photo-bioreactor (PBR) with 5% CO2. Moreover, CO2 assimilation rate was 2.748 g-CO2/g-DCW and 2.792 g-CO2/g-DCW under mixotrophic and autotrophic conditions, respectively. The biomass accumulation correlated with CA activity. In addition, the transcript levels of major genes in metabolic pathways of lutein and lipid were dramatically increased.