Bacterial transformations of naphthothiophenes

Naphthothiophenes are minor components of fossil fuels, and they can enter the environment from oil spills. Naphtho[2,1-b]thiophene, naphtho[2,3-b]thiophene, and 1-methylnaphtho[2,1-b]thiophene were synthesized and used in biodegradation studies with 1-methylnaphthalene (1-MN)-degrading Pseudomonas strains W1, F, and BT1. Cultures were incubated with one of the naphthothiophenes with or without 1-MN, acidified, and extracted with CH(inf2)Cl(inf2). The extracts were analyzed by gas chromatography with flame photometric and mass detectors to characterize sulfur-containing metabolites and with an atomic emission detector for quantification. Only strain W1 was able to grow on naphtho[2,1-b]thiophene, but strains F and BT1 cometabolized this compound if 1-MN was present. 1-MN was required by all three strains to metabolize naphtho[2,3-b]thiophene, which was more resistant to biodegradation than the [2,1-b] isomer. Two metabolites of naphtho [2,1-b]thiophene were purified, analyzed by (sup1)H nuclear magnetic resonance spectroscopy, and found to be 4-hydroxybenzothiophene-5-carboxylic acid (metabolite I) and 5-hydroxybenzothiophene-4-carboxylic acid (metabolite II). In cultures of strain W1 grown for 7 days on 52 (mu)mol of naphtho[2,1-b]thiophene, >84% of the substrate was degraded and metabolites I and II accounted for 19 and 9%, respectively, of the original amount of naphtho[2,1-b]thiophene. When 1-MN was present, strain W1 degraded >97% of the naphtho[2,1-b]thiophene and similar amounts of metabolite II were produced, but metabolite I did not accumulate. 1-MN was shown to promote the further degradation of metabolite I, but not of metabolite II, by strain W1. Thus, 1-MN enhanced the biodegradation of naphtho[2,1-b]thiophene. Approximately 70% of the 1-methylnaphtho [2,1-b]thiophene added to cultures of strain W1 with 1-MN was recovered as 4-hydroxy-3-methylbenzothiophene-5-carboxylic acid, the 3-methyl analog of metabolite I. The methyl substitution hindered further metabolism of 3-methyl-metabolite I even in the presence of 1-MN. Cometabolism of naphtho[2,3-b]thiophene yielded two products that were tentatively identified as 5-hydroxybenzothiophene-6-carboxylic and 6-hydroxybenzothiophene-5-carboxylic acids.

Anaerobic oxidation of n-dodecane by an addition reaction in a sulfate-reducing bacterial enrichment culture

We identified trace metabolites produced during the anaerobic biodegradation of H(26)- and D(26)-n-dodecane by an enrichment culture that mineralizes these compounds in a sulfate-dependent fashion. The metabolites are dodecylsuccinic acids that, in the case of the perdeuterated substrate, retain all of the deuterium atoms. The deuterium retention and the gas chromatography-mass spectrometry fragmentation patterns of the derivatized metabolites suggest that they are formed by C---H or C---D addition across the double bond of fumarate. As trimethylsilyl esters, two nearly coeluting metabolites of equal abundance with nearly identical mass spectra were detected from each of H(26)- and D(26)-dodecane, but as methyl esters, only a single metabolite peak was detected for each parent substrate. An authentic standard of protonated n-dodecylsuccinic acid that was synthesized and derivatized by the two methods had the same fragmentation patterns as the metabolites of H(26)-dodecane. However, the standard gave only a single peak for each ester type and gas chromatographic retention times different from those of the derivatized metabolites. This suggests that the succinyl moiety in the dodecylsuccinic acid metabolites is attached not at the terminal methyl group of the alkane but at a subterminal position. The detection of two equally abundant trimethylsilyl-esterified metabolites in culture extracts suggests that the analysis is resolving diastereomers which have the succinyl moiety located at the same subterminal carbon in two different absolute configurations. Alternatively, there may be more than one methylene group in the alkane that undergoes the proposed fumarate addition reaction, giving at least two structural isomers in equal amounts.

A review of the occurrence, toxicity, and biodegradation of condensed thiophenes found in petroleum

Condensed thiophenes comprise a significant portion of the organosulfur compounds in petroleum and in other products from fossil fuels. Dibenzothiophene (DBT) has served as a model compound in biodegradation studies for over two decades. However, until quite recently, few other organosulfur compounds were studied, and their fates in petroleum-contaminated environments are largely unknown. This paper presents a review of the types of organosulfur compounds found in petroleum and summarizes the scant literature on toxicity studies with condensed thiophenes. Reports on the biodegradation of benzothiophene, alkylbenzothiophenes, DBT, alkylDBTs, and naphthothiophenes are reviewed with a focus on the identification of metabolites detected in laboratory cultures. In addition, recent reports on quantitative studies with DBT and naphtho[2,1-b]thiophene indicate the existence of polar sulfur-containing metabolites that have escaped detection and identification.

Bacterial transformations of naphthothiophenes

Vol. 63, no. 9, p. 3468, Table 1, subheading under heading "Total recovery": "((delta)mol)" should read "((mu)mol)." [This corrects the article on p. 3463 in vol. 63.].

Bacterial transformations of 1,2,3,4-tetrahydrodibenzothiophene and dibenzothiophene

The transformations of 1,2,3,4-tetrahydrodibenzothiophene (THDBT) were investigated with pure cultures of hydrocarbon-degrading bacteria. Metabolites were extracted from cultures with dichloromethane (DCM) and analyzed by gas chromatography (GC) with flame photometric, mass, and Fourier transform infrared detectors. Three 1-methylnaphthalene (1-MN)-utilizing Pseudomonas strains oxidized the sulfur atom of THDBT to give the sulfoxide and sulfone. They also degraded the benzene ring to yield 3-hydroxy-2-formyl-4,5,6,7-tetrahydrobenzothiophene. A cell suspension of a cyclohexane-degrading bacterium oxidized the alicyclic ring to give a hydroxy-substituted THDBT and a ketone, and it oxidized the aromatic ring to give a phenol, but no ring cleavage products were detected. GC analyses with an atomic emission detector, using the sulfur-selective mode, were used to quantify the transformation products from THDBT and dibenzothiophene (DBT). The cyclohexane degrader oxidized 19% of the THDBT to three metabolites. The cometabolism of THDBT and DBT by the three 1-MN-grown Pseudomonas strains resulted in a much greater depletion of the condensed thiophenes than could be accounted for in the metabolites detected by GC analysis, but there was no evidence of sulfate release from DBT. These 1-MN-grown strains transiently accumulated 3-hydroxy-2-formylbenzothiophene (HFBT) from DBT, but it was subsequently degraded. On the other hand, Pseudomonas strain BT1d, which was maintained on DBT as a sole carbon source, accumulated 52% of the sulfur from DBT as HFBT over 7 days, and, in total, 82% of the sulfur from DBT was accounted for by the GC method used. Lyophilization of cultures grown on 1-MN with DBT and methyl esterification of the residues gave improved recoveries of total sulfur over that obtained by DCM extraction and GC analysis. This suggested that the further degradation of HFBT by these cultures leads to the formation of organosulfur compounds that are too polar to be extracted with DCM. We believe that this is the first attempt to quantify the products of DBT degradation by the so-called Kodama pathway.

Transformations of six isomers of dimethylbenzothiophene by three Pseudomonas strains

Dimethylbenzothiophenes are among the sulfur heterocycles in petroleum that are known to be degraded by microbial activity. Six of the 15 possible isomers of dimethylbenzothiophene were synthesized and used in bio-transformation studies with three Pseudomonas isolates that oxidize a variety of condensed thiophenes including methylbenzothiophenes and methyldibenzothiophenes. The isomers of dimethylbenzothiophene were chosen to have a variety of substitution patterns: both methyl groups on the thiophene ring (the 2,3-isomer); a methyl group on each of the rings (the 2,7-, 3,5-and 3,7-isomers); and both methyl groups on the benzene ring (the 4,6-and 4,7-isomers). Each isolate was grown on 1-methylnaphthalene or glucose in the presence of one of the dimethylbenzothiophenes and culture extracts were analyzed to identify nearly 30 sulfur-containing metabolites in total. Sulfoxides and sulfones were commonly found metabolites in culture extracts from the 2,3-, 2,7- and 3,7-isomers, whereas 2,3-diones, 3(2H)-ones and 2(3H)-ones were formed from the 4,6- and 4,7-isomers. High-molecular-weight products, some of which were tentatively identified as tetramethylbenzo[b]naphtho[1,2-d]thiophenes, were detected in the extracts of cultures incubated with 4,6- or 4,7-dimethylbenzothiophene. The methyl groups of all of the isomers, except 4,6-, were oxidized to give hydroxymethyl-methylbenzothiophenes and methylbenzothiophene-carboxylic acids, and these were the only products detected from the oxidation of 3,5-dimethylbenzothiophene.

Microbially Mediated Formation of Benzonaphthothiophenes from Benzo[ b ]thiophenes

Studies of the microbial metabolism of benzo[ b ]thiophene (molecular weight 134) by three Pseudomonas isolates showed the formation of benzothiophene sulfoxide, benzothiophene sulfone, and a sulfur-containing metabolite with a molecular weight of 234. Desulfurization of the high-molecular-weight product with nickel boride gave 1-phenylnaphthalene, indicating that the metabolite was benzo[ b ]naphtho[1,2- d ]thiophene. Similarly, the isolates were capable of producing the analogous dimethyl-substituted benzonaphthothiophenes from methylbenzothiophenes that had the methyl substitution on the benzene ring. The formation of benzo[ b ] naphtho[1,2- d ]thiophene was also observed when a petroleum-degrading mixed culture was incubated with benzothiophene-supplemented Prudhoe Bay crude oil. Investigations into the mechanism of formation of these high-molecular-weight compounds showed that they resulted from an abiotic, Diels-Alder-type condensation of two molecules of the sulfoxide, which were microbially produced from the respective benzothiophene, with the subsequent loss of two atoms of hydrogen and oxygen and one atom of sulfur. The condensation products also formed from the sulfoxides of benzothiophene and methylbenzothiophenes when the sulfoxides were enzymatically synthesized by oxidation of the benzothiophene with horse heart cytochrome c and H 2 O 2 .