Engineering ethanol production in a marine cyanobacterium Synechococcus sp. PCC7002 through simultaneously removing...

Photosynthetic production of ethanol with cyanobacteria utilizing CO₂ and solar energy could serve as a promising route for providing green biofuels. Comparing with Synechocystis sp. PCC6803, the most widely utilized cyanobacteria chassis, a marine cyanobacterium Synechococcus sp. PCC7002 (hereafter termed as PCC7002 for short) displayed better tolerances to high temperature and strong illuminations. To engineer ethanol production in PCC7002, we designed a strategy by simultaneous inactivation of glycogen synthesis pathways and introduction of two ethanolgenic cassettes. Two glgA genes responsible for elongation reaction of glycogen was selected as targets for blocking glycogen synthesis, and the removal of glycogen synthesis in PCC7002 caused growth retardation, which could be rescued by introducing two copies of ethanolgenic pathways. In addition, the synergy effects of blocked glycogen synthesis and gene dosage effects for ethanol synthesis resulted in significantly improved performances for ethanol production in the engineered strain, which synthesized 2.2 g/L ethanol in 10 days. In outdoor conditions, the PCC7002 derived cell factory still maintained considerable ethanolgenic capacities, accumulating 0.8 g/L ethanol in 7 days, with an average productivity of over 100 mg/L/day.