Xinyi Li,Tianbo Jia,Haiguang Zhu,Luhan Cai,Yubiao Lu,Jianxin Wang,Hengcong Tao,Peng Li
The CO 2 fixation mechanism by Alcaligenes faecalis ZS-1 in a biocathode microbial fuel cell (MFC) was investigated. The closed-circuit MFC (CM) exhibited a significantly higher CO 2 fixation rate (10.7%) compared to the open-circuit MFC (OC) (2.0%), indicating that bioelectricity enhances CO 2 capture efficiency. During the inward extracellular electron transfer (EET) process, riboflavin concentration increased in the supernatant while cytochrome levels decreased. Genome sequencing revealed diverse metabolic pathways for CO 2 fixation in strain ZS-1, with potential dominance of rTCA and C4 pathways under electrotrophic conditions as evidenced by significant upregulation of the ppc gene. Differential metabolite analysis using LC-MS demonstrated that CM promoted upregulation of various lipid metabolites. These findings collectively highlight that ZS-1 simultaneously generated electricity and fixed CO 2 and that the ppc associated with bioelectricity played a critical role in CO 2 capture. In conclusion, bioelectricity resulted in a significant enhancement in the efficiency of CO 2 fixation and lipid production.
5-Aminolevulinic acid (5-ALA) is an important non-proteinogenic amino acid with wide applications in agriculture and medicine. To achieve high-level microbial production, this study established a dual-pathway reconstruction strategy in Escherichia coli by integrating the endogenous C5 pathway with an inducible exogenous C4 pathway. Multi-copy overexpression of gltX , hemA , and hemL , combined with enhanced glutamate supply and the introduction of a non-oxidative glycolysis pathway, effectively increased the C5 pathway flux and carbon efficiency, while product toxicity was significantly alleviated by strengthening efflux mechanisms and oxidative stress tolerance. A quorum sensing–based regulatory system was employed to dynamically regulate hemB expression, thereby balancing cell growth and 5-ALA biosynthesis, and a controlled glycine feeding strategy specifically activated the C4 pathway during the later fermentation stage, forming a stage-specific dynamic activation mechanism. Promoter regulation of sucC/sucD expression and enhanced endogenous PLP biosynthesis further stabilized the C4 flux. Fed-batch fermentation in a 5 L bioreactor resulted in a final 5-ALA titer of 37.34 g/L, demonstrating the industrial potential of this systems metabolic engineering strategy combining dual pathways and stage-specific activation control.
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