Biofilm engineering to improve succinic acid production in Escherichia coli by enhancing extracellular polysaccharide synthesis

Biofilms play crucial roles in enhancing microbial tolerance to environmental stress. Biofilm engineering in industrial microorganisms has been a promising and efficient approach to improve the production of metabolites. In this study, the psl gene cluster from Pseudomonas aeruginosa, for extracellular polysaccharide synthesis, was first introduced in a succinic acid (SA) producing Escherichia coli strain to enhance the biofilm formation ability. The engineered strain Suc260 (pslA-J) showed the improved tolerance to harsh environments and improved SA synthesis capability. Compared to the control, strain Suc260 (pslA-J) produced 70.54 g/L of SA from glucose in a 5 L bioreactor, representing an increase of 13.41 %. To further enhance the synthesis efficiency of SA, a cell immobilization fermentation system based on biofilms on alginate beads was designed. Finally, 62.66 g/L of SA with a yield of 0.76 g/g was produced from wheat straw hydrolysate in a 5 L bioreactor at the optimal pH of 6.8. When the pH was adjusted to a lower value (pH 6.0), the SA production and yield still reached 57.67 g/L and 0.75 g/g, respectively, representing 28.96 % and 42.15 % higher than those of the control strain. This study provides an efficient platform technology for the production of bio-based SA in large scale.