Recombinant cyanobacteria cultured in CO₂ and seawater as feedstock for coproduction of acetoin and succinate by engineered Enterobacter cloacae

In this work, engineered freshwater cyanobacteria (Synechococcus elongatus PCC7942-hspA) were cultivated with CO₂ and seawater to harvest biomass, optimize biomass hydrolysis conditions to increase the sugar concentration in the hydrolysate and use it as a feedstock for the coproduction of acetoin and succinate. Since the hydrolysate contains glucose and xylose, to improve the utilization efficiency of the strain mixed sugar, Enterobacter cloacae (strain CL80) in which the budC, ldhA, and ptsG genes were knocked out was constructed. When using cyanobacteria biomass hydrolysate as the fermentation feedstock of CL80, the concentrations of acetoin and succinate were 10.55 and 1.8 g L⁻¹, respectively. This work is the first attempt to use freshwater cyanobacteria biomass hydrolysate obtained by culture with CO₂ and seawater as the feedstock for the coproduction of acetoin and succinate, and it will provide a practical strategy for reducing carbon dioxide emissions and producing biobased value-added products by the biorefinery method.