Overexpression of fatty acid synthesis genes in Synechocystis sp. PCC 6803 with disrupted glycogen synthesis increases lipid production with further enhancement under copper induced oxidative stress.

In the present study, fatty acid synthesis genes such as alpha and beta subunits of acetyl CoA carboxylase (accA and accD) were overexpressed in the glgC (Glucose-1-phosphate adenylyltransferase) knockout Synechocystis sp. PCC 6803. The biomass and lipid contents were evaluated in both the wild type and the engineered strains after copper treatment. The maximum lipid production of 0.981 g/L with the productivity of 81.75 mg/L/d was obtained from the copper treated ΔglgC + A-OX strain, which showed a 3.3-fold increase compared to the untreated wild type with satisfactory biodiesel properties. After copper treatment the knockout strain improved the unsaturated fatty acids level contributing to the increase of the saturated and mono-unsaturated ratio with improvement of the fuel quality. Copper induced oxidative stress also improved the photosynthetic pigments in engineered strains leading to increased tolerance against oxidative stress in the engineered strains. The copper treatment increased the antioxidant enzyme activities in the engineered strains especially in ΔglgC + A-OX strain. The carbon flux to lipid synthesis was enhanced by the engineered strains particularly with the knockout-overexpression strains. The Synechocystis sp. PCC 6803 engineered with ΔglgC + A-OX showed high potential for fuel production after the copper treatment.
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