Glucose-assisted trophic conversion of Chlamydomonas reinhardtii by expression of glucose transporter GLUT1

The use of genetic engineering techniques to alter the nutritional patterns of microalgae is a key means of enhancing microalgal biomass, as it enables the highly efficient heterotrophic growth of microalgae via the utilisation of organic carbon sources, especially glucose. To investigate the effects of the expression of the glucose transporter on the growth of the model alga, Chlamydomonas reinhardtii, we transformed C. reinhardtii using the human GLUT1 gene, regulated by the Hsp70, PsaD, and Arg7 promoters, and obtained engineered algae after screening. The engineered algae showed better growth than the control algae under both heterotrophic and mixotrophic growth conditions. The engineered alga in which the GLUT1 gene was regulated by the Arg7 promoter exhibited the best growth. Although the engineered algae exhibited heterotrophic growth in complete darkness by using glucose as the carbon source, their growth rates and biomass were relatively low compared to those of the control. Analysis of the glucose transport ability of the engineered algae revealed that glucose was successfully transported to the cytoplasm via the glucose transporters, but was unable to enter the chloroplasts, which could explain the slow heterotrophic growth of the engineered algae.