Complete degradation of bisphenol A and nonylphenol by a composite of biogenic manganese oxides and Escherichia coli cells with surface-displayed multicopper oxidase CotA

Abstract

Endocrine-disrupting chemicals (EDCs) are a large group of environmental toxicants that pose serious risks to public health. In this study, we report a new method for the complete degradation of EDCs using a dual oxidation-action composite of biogenic manganese oxides and engineered Escherichia coli cells with surface-expressed multicopper oxidase CotA. The cotA gene from a Mn2+-oxidizing bacterium was constructed as a fusion gene “inaQ-N/cotA” with an anchoring motif inaQ-N from Pseudomonas syringae and was expressed in E. coli cells to display catalytic CotA on the cell surface. Under prolonged Mn2+-enriched culturing conditions, the engineered cells were capable of forming microspherical aggregated composites that were mainly composed of ramsdellite (MnO2). The ability of the composite to degrade two EDCs, bisphenol A (BPA) and nonylphenol (NP), was investigated. GC–MS assays identified 7 and 10 degraded intermediates using the 13C isotope from 13C-labeled BPA and 13C-labeled NP, respectively. The appearance of 13CO2 from both reaction mixtures revealed mineralization pathways of BPA and NP by this composite. Bioassays using Caenorhabditis elegans as an indicator organism demonstrated that the estrogenic activity of BPA and NP was eliminated by these degradation processes. The reaction of the composite proceeded at an acidic pH and room temperature. A consecutive three-round treatment process showed comparable levels of degradation by the composite in repeated reactions and showed that the activity could be easily recovered. Moreover, the superoxide radical levels of BPA-degradation and NP-degradation were monitored during the 24 h reaction time, and possible BPA-degradation and NP-degradation pathways by the composite were proposed.