Utilizing Ribose 1,5-Bisphosphate Isomerase and RuBisCO-Equipped Escherichia coli Nissle for Low-Carbon Footprint GABA Production

Escherichia coli Nissle 1917 (EcN), the only probiotic E. coli, has been exploited as a promising chemical bioproducer due to possessing unique mutations under acidic conditions. To bolster its sustainability, a novel CO₂-recycling system was reconstructed by coexpressing ribose-1,5-bisphosphate isomerase (R15Pi) and ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) (i.e., RR plasmid). The function of RR was examined through the transcription level of the R15P-generating gene (phnN), showing higher mRNA in EcN. Afterward, the RR-equipped EcN strain was utilized for recycling CO₂ release during γ-aminobutyric acid (GABA) synthesis, improving the yield by 12, 12.5, and 14% through CO₂ assimilation in glucose, acetate, and glycerol medium, respectively. RR with a low copy GadB plasmid (i.e., RR+LG strain) successfully assimilated CO₂ of 27–37% within the three mediums. The artificial CO₂-fixing system was successfully reconstructed in EcN via R15Pi and RuBisCO, thus manifesting the prospects of EcN as a low-carbon-featuring microbial cell factory by a new pathway.