Tuning the metabolic flux of Rhodopseudomonas palustris 42OL in bioelectrochemical systems for enhanced brewery wastewater valorization

This study investigates whether bioelectrochemical stimulation can redirect electron flow in the purple phototrophic bacteria Rhodopseudomonas palustris 42OL to enhance the production of biomass, bio-hydrogen (H₂), and polyhydroxybutyrate (PHB). R. palustris 42OL was cultivated in a single-chamber bioelectrochemical system (BES) fed with brewery wastewater under cathodic potentials of −0.3, −0.6, and − 0.8 V (vs Ag/AgCl). Metabolic shifts were evaluated by RT-qPCR targeting three key genes: nifH (responsible for H2 evolution via nitrogenase), phaC (which regulates PHB synthesis), and rbcL (which controls carbon fixation and biomass growth). Results demonstrate that polarization at −0.3 and − 0.6 V (vs Ag/AgCl) significantly enhances system performance. Biomass production peaked at −0.3 V (0.91 g/L), representing a 60% increase over the electrode-free control. Polarization at −0.6 V maximized byproduct generation, yielding 70.35 mL H2/L (a 511% increase compared to the control) and 115.3 mg PHB/g VSS (a 250% increase). Molecular expression supported these trends, revealing that applied potentials actively regulate intracellular electron partitioning. These findings demonstrate that controlled cathodic stimulation is a powerful tool for directing microbial metabolism toward targeted resource recovery. This proof of concept provides the essential foundation for future research and a possible scale-up, advancing the transition toward sustainable wastewater valorization.