Production of protocatechuic acid from terephthalic acid by engineered Shewanella oneidensis MR1 and its application to azo dye reduction with bioelectrochemical systems.

As terephthalic acid (TPA), a major monomer of poly(ethylene terephthalate) (PET) and plasticizers, is increasingly detected in environmental matrices such as wastewater and surface water following plastic degradation, it highlights the need for sustainable valorization strategies. In this study, Shewanella oneidensis MR-1 was engineered to enable TPA uptake and conversion by introducing the tpaK transporter from Rhodococcus jostii RHA1 and the tphAabcB operon from Comamonas sp. E6. The engineered strain successfully converted TPA into protocatechuic acid (PCA), achieving a maximum titer of 2.31 ± 0.02 mM with a conversion yield of 46.36 ± 1.58% under optimized conditions. Notably, PCA acted as a redox-active mediator that significantly enhanced azo dye reduction, and in situ PCA production further improved decolorization compared with the wild-type strain. Electrochemical analyses confirmed the reversible redox behavior of PCA, whereas TPA exhibited negligible electrochemical activity. These results demonstrate a previously unexplored link between plastic-derived monomer bioconversion and extracellular electron transfer enhancement, suggesting a promising route for coupling plastic waste valorization with redox-driven environmental remediation processes.