Fig. 3.

Examples on the application of MES for chemical production.

MES has been demonstrated to facilitate chemical production by providing electrons or electron sinks to microbes, ensuring an adequate supply of redox equivalents in the form of NAD(P)H and NAD(P)⁺, thus supporting redox-intensive biochemical reactions. Electrons have been transferred either directly through electron conduit complexes (ECC, such as MtrCAB) or indirectly through redox-active mediators (e.g. H₂, flavins, phenazines, neutral red and methyl viologen) that shuttle between their oxidized (MED_ox) and reduced (MED_red) forms. The transfer of electrons between electrodes and microbes has boosted the utilization of waste-derived feedstocks such as CO₂, lactate, glycerol and acetate. Moreover, both native pathways and metabolically engineered heterologous pathways have benefited from EET, receiving the necessary redox power for biochemical reactions and improving the production of a wide range of chemicals. By coupling EET-mediated utilization of renewable carbon sources with synthetic biology, MES using engineered microbes has demonstrated potential as a viable solution to meet the world's chemical needs while addressing environmental and energy issues. FAR, fatty acyl-CoA reductase; TS, terpene synthases; PHA, polyhydroxyalkanoate; 1,3-PDO, 1,3-propanediol; 3-HP, 3-hydroxypropionic acid.