Biotransformation of benzothiophene by isopropylbenzene-degrading bacteria

Abstract

Isopropylbenzene-degrading bacteria, including Pseudomonas putida RE204, transform benzothiophene to a mixture of compounds. Induced strain RE204 and a number of its TnS mutant derivatives were used to accumulate these compounds and their precursors from benzothiophene. These metabolites were subsequently identified by 1H and 13C nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. When strain RE204 was incubated with benzothiophene, it produced a bright yellow compound, identified as trans-4-[3-hydroxy-2-thienylJ-2-oxobut-3-enoate, formed by the rearrangement of cis-4-(3-keto-2,3-dihydrothienyl)-2-hydroxybuta-2,4-dienoate, the product of 3-isopropylcatechol-2,3-dioxygenase-catalyzed ring cleavage of 4,5-dihydroxybenzothiophene, as well as 2-mercaptophenylglyoxalate and 2'-mercaptomandelaldehyde. A dihydrodiol dehydrogenase-deficient mutant, strain RE213, converted benzothiophene to cis-4,5-dihydroxy4,5-dihydrobenzothiophene and 2'-mercaptomandelaldehyde; neither trans-4-[3-hydroxy-2-thienyl]-2-oxobut-3-enoate nor 2-mercaptophenylglyoxalate was detected. Cell extracts of strain RE204 catabzed the conversion of cis-4,5-dihydroxy-4,5-dihydrobenzothiophene to trans-4-[3-hydroxy-2-thienyl]-2-oxobut-3-enoate in the presence of NAD+. Under the same conditions, extracts of the 3-isopropylcatechol-2,3-dioxygenasedeficient mutant RE215 acted on cis-4,5-dihydroxy-4,5-dihydrobenzothiophene, forming 4,5-dihydroxybenzothiophene. These data indicate that oxidation of benzothiophene by strain RE204 is initiated at either ring. Transformation initiated at the 4,5 position on the benzene ring proceeds by three enzyme-catalyzed reactions through ring cleavage. The sequence of events that occurs following attack at the 2,3 position of the thiophene ring is less clear, but it is proposed that 2,3 dioxygenation yields a product that is both a cis-dihydrodiol and a thiohemiacetal, which as a result of this structure undergoes two competing reactions: either spontaneous opening of the ring, yielding 2'-mercaptomandelaldehyde, or oxidation by the dihydrodiol dehydrogenase to another thiohemiacetal, 2-hydroxy-3-oxo-2,3-dihydrobenzothiophene, which is not a substrate for the ring cleavage dioxygenase but which spontaneously opens to form 2-mercaptophenylglyoxaldehyde and subsequently 2-mercaptophenylglyoxalate. The yellow product, trans4[3-hydroxy-2-thienylJ-2-oxobut-3-enoate, is a structural analog of nins-o-hydroxybenzylidenepyruvate, an intermediate of the naphthalene catabolic pathway; extracts of recombinant bacteria containing zns-o-hydroxybenzylidenepyruvate hydratase-aldolase catalyzed the conversion of ans-4-[3-hydroxy-2-thienyl]-2-oxobut-3-enoate to 3-hydroxythiophene-2-carboxaldehyde, which could then be further acted on, in the presence of NAD+, by extracts of recombinant bacteria containing the subsequent enzyme of the naphthalene pathway, salicylaldehyde dehydrogenase.Sulfur-containing heterocyclic chemicals, including benzothiophene (benzo-[b]-thiophene, thianaphthene), comprise a relatively sm...

Aerobic Degradation of Petroleum Components by Microbial Consortia

“…However, no bacterial strain has been found to grow on benzothiophenes as the sole carbon source, and all reported biotransformations of benzothiophenes are based on cometabolism. Attacks on the thiophene ring of benzothiophenes lead to the formation of sulfoxides and sulfones, or to ring opening and the formation of 2-mercaptomandelaldehyde and 2-mercaptophenylglyoxalate [158][159][160]. Catabolism of dibenzothiophene is catalyzed by distinct enzymes in two pathways (Scheme 7).…”

Microbial transformation of benzothiophenes, with carbazole as the auxiliary substrate, by Sphingomonas sp. strain XLDN2-5

“…Six metabolites of BT were detected by GC-MS: BTO 2 and 2-mercaptobenzoic acid were identified by comparison of their retention times and mass spectra with those of authentic compounds; 2-hydroxybenzothiophene, 3-hydroxybenzothiophene, benzothiophene-2,3-dione and BTO were identified by comparison of their mass spectra with published data (Saftić et al, 1992;Eaton & Nitterauer, 1994;Kropp et al, 1994b;Gilbert et al, 1998). These results indicate that strain XLDN2-5 is able to catalyse lateral dioxygenation and S oxidation on the thiophene ring of BT.…”

“…However, no bacterial strain has been found that is able to grow on benzothiophenes as the sole carbon source, and all reported biotransformations of benzothiophenes are based on cometabolism. Attacks on the thiophene ring of benzothiophenes lead to the formation of sulfoxides and sulfones, or to ring opening and the formation of 2-mercaptomandelaldehyde and 2-mercaptophenylglyoxalate (Saftić et al, 1992;Eaton & Nitterauer, 1994;Gilbert et al, 1998). Interestingly, it has been reported that BTO is trapped as a Diels-Alder-type disulfoxide cycloadduct, which yields (Kropp et al, 1994b).…”

Sonochemical Reaction Mechanism of a Polycyclic Aromatic Sulfur Hydrocarbon in Aqueous Phase

“…The mass spectra were compared with the computer database of the National Institute of Science and Technology (NIST) mass spectral library and the published mass spectra of BT intermediates. 22,23 The mass spectra of peaks at retention times 6.57, 10.00, and 11.04 min have a near 100 : 4.4 ratio based on the isotope ion peaks at m/z values of M + and (M+2) + . This ratio indicates the presence of a sulfur atom (Figure 1b-e).…”

“…22 The m/z value of the molecular ion of the peak at 11.04 min (Figure 1e Figure 1d. 23 The mass spectra correspond potentially to the isomers 2-, 3-, 4-, 5-, 6-, or 7-hydroxybenzothiophene. Among them, the peaks at 10.07 and 10.25 min appear to be 2-hydroxy-benzothiophene and 3-hydroxybenzothiophene.…”