Scientists at the US Energy Department’s National Renewable Energy Laboratory (NREL) in Colorado, US, developed a method for genetically engineering cyanobacteria to harvest sunlight and CO2 to produce ethylene and ethylene derivatives. The research is a finalist in the Mechanical Devices/Materials category for an R&D 100 award (the “Oscars” of innovation). Researchers in Japan in the late 1990s discovered a blue-green alga, Synechococcus sp. PCC 7942, could be modified to produce ethylene via photosynthesis by the introduction of the gene that codes for an ethyleneforming enzyme (EFE). But that strain ran into problems as the amount of ethylene produced declined over time and by the fourth generation of the cyano- petrobacterium production stopped entirely. Building on that research, Yu turned his attention to a different cyanobacterium, Synechocystis sp. PCC 6803.
Ethylene already can be made without fossil fuels through the conversion of bioethanol, but that requires making bioethanol as well as an additional step. Yu’s research showed ethylene could be made directly and continuously from cyanobacterium. Normally, algae convert carbon dioxide during photosynthesis into biomass or sugars. But Yu’s method redirected the cyanobacterium to use a portion of the CO2 to produce ethylene. Since his initial discovery in 2010, Yu has managed to increase the amount of ethylene produced in the laboratory by more than a thousand-fold, to 35 milligrams per liter per hour. His goal is to reach 50 milligrams by the end of the year. Getting the cyanobacterium to produce ethylene requires the introduction of alpha ketoglutarate and other metabolites as substrates on which the enzyme acts. Yu found an increase in the amount of enzyme triggered a proportional increase in the amount of ethylene produced. Yu has been able to keep the cyanobacterium producing ethylene even as the organism itself continues to grow. NREL is considering using a pond covered with a plastic tent to trap the ethylene for commercializing the technology.