Functional integration of the HUP1 hexose symporter gene into the genome of C. reinhardtii: Impacts on biological H2 production

Phototrophic organisms use photosynthesis to convert solar energy into chemical energy. In nature, the chemical energy is stored in a diverse range of biopolymers. These sunlight-derived, energy-rich biopolymers can be converted into environmentally clean and CO2 neutral fuels. A select group of photosynthetic microorganisms have developed the ability to extract and divert protons and electrons derived from water to chloroplast hydrogenase(s) to produce molecular H2 fuel. Here, we describe the development and characterization of C. reinhardtii strains, derived from the high H2 production mutant Stm6, into which the HUP1 (hexose uptake protein) hexose symporter from Chlorella kessleri was introduced. The isolated cell lines can use externally supplied glucose for heterotrophic growth in the dark. More importantly, external glucose supply (1mM) was shown to increase the H2 production capacity in strain Stm6Glc4 to ∼150% of that of the high-H2 producing strain, Stm6. This establishes the foundations for a new fuel production process in which H2O and glucose can simultaneously be used for H2 production. It also opens new perspectives on future strategies for improving bio-H2 production efficiency under natural day/night regimes and for using sugar waste material for energy production in green algae as photosynthetic catalysts.