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Bio-based photosynthetic conversion of CO2 and water to replace petroleum feedstock on an industrial scale

Stage: Development

Alpha-ketoglutarate (AKG) is widely used as an organic synthesis intermediate, a medical and biochemical reagent, and as a nutritional additive in food and sports drinks.  Typically, it is produced from a derivative of petroleum and concentrated hydrochloric acid.  However, the rising cost of petroleum has led to the exploration and development of alternative, biological production systems for fuels and chemicals.  Recently, a number of organizations have successfully applied closed-loop photobioreactors to the production of hydrocarbon feedstocks.  One such system developed at NREL utilizes the freshwater photosynthetic cyanobacterium, Synechosystis, to produce AKG in an environmentally friendly and sustainable process on an industrial scale.

Through metabolic engineering of a strain of Synechocystis, a gene delete mutant was derived that shows robust growth similar to the wild-type under standard laboratory conditions.  However, metabolite distribution is altered in this mutant.  In addition to genetic modification, the distribution can be manipulated by changing growth conditions.  Under specific conditions the mutant produces high levels of the AKG, about 30% of cell dry weight, which is on the order of 10,000-fold increase from the wild type. The production of AKG has been identified and quantified by three independent techniques: GC/MS, H+-NMR, and HPLC.

The extrapolated photosynthetic production rate of the intermediate is at least 150 grams per day per 1,000L reactor at a cell density of 1 gram dry weight per liter. This genetically engineered cyanobacterial strain has potential application for the production of the AKG in a continuous "milking" (verses batch culture) process, which improves energy conversion efficiency and reduces operational cost.  The principle established in this innovation can be applied to other cyanobacteria and algae for similar production.

For more information, contact Eric Payne at Eric.Payne@nrel.gov.

ROI 11-18

U.S. Patent # 9,309,541; 9,914,947

Applications and Industries

  • Medical and biochemical reagents
  • Nutritional additives


  • Environmentally friendly and sustainable process
  • Milking process reduces operation cost and increases energy conversion efficiency