Different mechanisms of biotransformation of bisphenol A by the biphenyl-degrading Cupriavidus basilensis SBUG 290 lead to detoxification and reduction of estrogenicity

A bacterial strain identified as Cupriavidus basilensis uses aromatic compounds as carbon and energy sources and has a high capability to transform the structurally related and hormonally active substance bisphenol A (BPA). Biphenyl-grown and phenol-grown cells converted BPA to five products within 24 h of incubation representing four different transformation pathways: (a) ring hydroxylation, (b) ring fission, (c) transamination and acetylation, and (d) dimerization. Products of the ring fission pathway were non-toxic and all five products exhibited a significantly reduced estrogenic activity compared to BPA. Cell cultivation in nutrient broth resulted in lower product quantities and dimerization was not proved. Thus the question arose whether enzymes of the biphenyl or phenol degradation pathway are involved in the transformation of BPA. Proteomic analyses revealed the constitutive expression of biphenyl degrading enzymes and indicated that the 2,3 dihydroxybiphenyl-1,2-dioxygenase might catalyse the meta-cleavage of the aromatic ring of BPA while enzymes of other pathways seemed to be involved in ring hydroxylation.