Electro-fermentation Enhanced Biochemical Production

Abstract

In light of the chemical industry's persistent reliance on fossil fuels, new biocatalysis-driven processes have become central to sustainable chemical manufacturing. Among them, electro-fermentation has emerged as a promising process that augments conventional fermentation by coupling polarised electrodes to microbial metabolism to modulate the extracellular redox environment and, in turn, intracellular cofactor levels. This integration mitigates redox and energetic constraints and enables deliberate steering of metabolism toward desired products.

This dissertation explored electro-fermentation in anodic configuration to enhance biochemical production under oxygen limitation in the industrially relevant bacterium <i>Bacillus subtilis</i> and in cathodic configuration with mixed microbial communities. Investigations of alternative electron acceptors showed that <i>B. subtilis</i> requires oxygen to sustain its metabolism. Under oxygen limitation, a poised anode potential redirected metabolism from lactate to acetoin, achieving an overall acetoin yield of 0.78 ± 0.04 mol_product/mol_gIucose. Combined with metabolic engineering and pH optimisation, an engineered <i>B. subtilis</i> strain respired on an anode without oxygen, selectively producing 2,3-butanediol (maximum carbon selectivity = 77.08 ± 0.55%; yield = 0.49 ± 0.07 mol_product/mol_glucose). Anodic respiration was strongly influenced by pH, and by elevating pH to 6.5 and 7.5 improved glucose consumption and 2,3-butanediol production was obtained relative to uncontrolled pH. Cathodic mixed culture electro-fermentation with xylose showed that repeated-batch operation steered metabolism toward propionate and butyrate, resulting a 1.6-fold higher propionate yield (0.09 ± 0.05 mol_product/mol_xylose) than open circuit controls, and enrichment of <i>Costridium</i> was associated with cathode-assisted metabolism Together, these findings highlight electro-fermentation as a promising approach to reduce oxygen dependence in industrial biotechnology while enhancing biochemical production from renewable feedstocks.