Non-native Pathway Engineering with CRISPRi for Carbon Dioxide Assimilation and Valued 5-Aminolevulinic Acid Synthesis in Nissle.

Carbon dioxide emission and acidification during chemical biosynthesis are critical challenges toward microbial cell factories' sustainability and efficiency. Due to its acidophilic traits among workhorse lineages, the probiotic Nissle (EcN) has emerged as a promising chemical bioproducer. However, EcN lacks a CO-fixing system. Herein, EcN was equipped with a simultaneous CO fixation system and subsequently utilized to produce low-emission 5-aminolevulinic acid (5-ALA). Two different artificial CO-assimilating pathways were reconstructed: the novel ribose-1,5-bisphosphate (R15P) route and the conventional ribulose-5-phosphate (Ru5P) route. CRISPRi was employed to target the AB and genes in order to redirect the carbon flux. As expected, the CRISPRi design successfully strengthened the CO fixation. The CO-fixing route via R15P resulted in high biomass, while the engineered Ru5P route acquired the highest 5-ALA and suppressed the CO release by 77%. CO fixation during 5-ALA production in EcN was successfully synchronized through fine-tuning the non-native pathways with CRISPRi.