Metabolic engineering of E. coli for producing phloroglucinol from acetate

Phloroglucinol is a three-hydroxyl phenolic compound and has diverse physiological and pharmacological activities such as antivirus and anti-inflammatory activities. Chemical synthesis of phloroglucinol suffered from many drawbacks such as high cost and environmental pollution. To avoid the above issues, microbial phloroglucinol biosynthesis was successfully accomplished in this study, while the abundant and low-cost acetate was used as the main carbon source. Firstly, the toxicity of phloroglucinol was tested, and E. coli BL21(DE3) could tolerate 5 g/L phloroglucinol. The ability of phloroglucinol synthase (PhlD) for catalyzing malonyl-CoA to phloroglucinol was confirmed, and E. coli BL21(DE3) expressing PhlD and acetyl-CoA carboxylase (ACCase) could produce 1107 ± 12 mg/L phloroglucinol from glucose. Then, E. coli BL21(DE3) was engineered to utilize acetate to produce 228 ± 15 mg/L phloroglucinol. Then, the endogenous citrate synthase (GltA) which could catalyze oxaloacetate and acetyl-CoA generated from acetate to citrate was knocked down by CRISPRi system in order to enhance the carbon flux for phloroglucinol production, and the titer was improved to 284 ± 8 mg/L. This work demonstrated that acetate could be used as low-cost substrate to achieve the biosynthesis of phloroglucinol and provided an example of effective utilization of acetate.