In view of the increasing demand for biofuels and sustainable chemical feedstocks, we develop a new approach in agriculture, aiming to harness photosynthetic microorganisms such as microalgae and cyanobacteria. In stark contrast to land plants, these microbes can be harvested daily. Furthermore, the advanced genetic tools gained so far for these microbes, which gave one microalgae species, Chlamydomonas reinhardtii the unique name “the green yeast” allow reengineering into efficient green chemistry reactors for sustainable and clean production of chemicals and fuels. While photosynthetic energy, channeled through electron flow, is primarily used to power the fixation of CO2 into organic matter, it can also power other limited processes, such as H2 production via the enzyme Hydrogenase.
Photobiological Hydrogen (H2) production from green microalgae holds great promise for sustainable production of a clean, zero carbon footprint fuel. However, in nature, the process of H2 production is temporary, lasting for 2 minutes. Thereafter, it ceases due to electron loss to competing processes, mainly the Calvin cycle, and later on, due to an accumulation of inhibitory concentrations of oxygen. The key for diverting the energy from CO2 fixation to H2 production or other chemicals is to unveil and exploit new photosynthetic hotspots, where electron flow can be redirected towards improved enzymes. Recently, we found that a Chlamydomonas mutant in the Proton-Gradient-Regulation-Protein-5 (pgr5) gene harbors faster respiration and a slower Calvin cycle allowing scalable (culture volumes of 1L) continuous production of H2 under ambient mixotrophic conditions for a duration of 12 days. This achievement allows engineering studies which focus on scale up of the process.