Abstract
Comparative analyses determined the relationship between the structure of bisphenol A (BPA) as well as of seven bisphenol analogues (bisphenol B (BPB), bisphenol C (BPC), bisphenol E (BPE), bisphenol F (BPF), bisphenol Z (BPZ), bisphenol AP (BPAP), bisphenol PH (BPPH)) and their biotransformability by the biphenyl-degrading bacterium Cupriavidus basilensis SBUG 290. All bisphenols were substrates for bacterial transformation with conversion rates ranging from 6 to 98% within 216 h and 36 different metabolites were characterized. Transformation by biphenyl-grown cells comprised four different pathways: (a) formation of ortho-hydroxylated bisphenols, hydroxylating either one or both phenols of the compounds; (b) ring fission; (c) transamination followed by acetylation or dimerization; and (d) oxidation of ring substituents, such as methyl groups and aromatic ring systems, present on the 3-position. However, the microbial attack of bisphenols by C. basilensis was limited to the phenol rings and its substituents, while substituents on the carbon bridge connecting the rings were not oxidized. All bisphenol analogues with modifications at the carbon bridge could be oxidized up to ring cleavage, while substituents at the 3-position of the phenol ring other than hydroxyl groups did not allow this reaction. Replacing one methyl group at the carbon bridge of BPA by a hydrophobic aromatic or alicyclic ring system inhibited both dimerization and transamination followed by acetylation. While most of the bisphenol analogues exhibited estrogenic activity, four biotransformation products tested were not estrogenically active.
Highlights
For more than six decades, bisphenol A (BPA) has been used in the production of polycarbonate plastics and epoxy resins (EPA 2014; Hoekstra and Simoneau 2013; Usman and Ahmad 2016) with an annual production of more than 3.8 million tons (Michałowicz 2014)
We narrow some of these gaps by investigating the biotransformation of seven bisphenol analogues by the biphenyldegrading bacterium Cupriavidus basilensis SBUG 290 that was isolated from environmental samples and is able to transform BPA efficiently (Zühlke et al 2017)
We investigated the biotransformation of seven BPA analogues, which differ from BPA by the addition or by the lack of substituents at the ring linking carbon bridge or at the phenol rings
Summary
For more than six decades, bisphenol A (BPA) has been used in the production of polycarbonate plastics and epoxy resins (EPA 2014; Hoekstra and Simoneau 2013; Usman and Ahmad 2016) with an annual production of more than 3.8 million tons (Michałowicz 2014). Many of them have been documented in various environmental compartments like indoor dust, sediment, sludge, and surface waters, in foods and food containers, personal care products, as well as in human samples as comprehensively summarized by Chen et al (2016). Many of these substances constitute serious public health risks. Our objectives were (i) to determine the biotransformation pathway of the various compounds by structure elucidation of the transformation products formed, (ii) to establish principles of the structure-biotransformation-relationship, and (iii) to determine the estrogenicity of the transformation products compared to that of the bisphenol analogues
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