Coproduction of Bioelectricity and Acetoin by Unbalanced Fermentation of Glycerol in Shewanella oneidensis Based on a Genome-Scale Metabolic Network

Unbalanced fermentation is a promising innovative strategy for biotechnological production processes. Guided by the genome-scale metabolic network iLJ1162, the central carbon metabolism was rewired to enhance the synthesis of (3R)-acetoin and link it to establish efficient extracellular electron transfer through unbalanced fermentation in Shewanella oneidensis. We first successfully constructed an engineered strain using glycerol as the sole carbon source to coproduce (3R)-acetoin and bioelectricity. Key engineering targets for (3R)-acetoin synthesis and bioelectricity were predicted by iLJ1162, including the glycolysis module (gapA and pgk), the serine bypass module (glyA, serA, serB, and serC), and the pyruvate fermentation module (fdh). As a result, we discovered that the serB gene was conducive to the production of bioelectricity (35.91 ± 1.04 mW m–2), and serC promoted the synthesis of (3R)-acetoin (213.5 ± 6.07 mg L–1) in the serine bypass module. However, the low power output capacity became the bottleneck, limiting the acetoin yield. To further balance the reducing force, we developed functional electrodes composed of carbon nanotubes and graphene oxide, as well as electron shuttles for improving electricity generation. The power density and the titer of (3R)-acetoin, respectively, reached up to 149.72 ± 2.72 mW m–2 and 313.61 ± 5.48 mg L–1, which were 5.08 and 1.00 times higher than in the control. The optical purity of the resulting (3R)-acetoin surpassed 90%. This study provides a new paradigm for achieving the "balance" between high value-added products with low reducibility and electricity production in unbalanced fermentation while boosting the titer of products based on model guidance.