Aerobic microbial metabolism of some alkylthiophenes found in petroleum

Abstract

Six alkylthiophenes, 2-hexadecyl-5-methylthiophene (I), 2-methyl-5-tridecylthiophene (II) and 2-butyl-5-tridecylthiophene (III), 2-(3,7-dimethyloctyl)-5-methylthiophene (IV), 2-methyl-5-(3,7,11,15-tetramethylhexadecyl)thiophene (V) and 2-ethyl-5-(3,7,11,15-tetramethylhexadecyl)thiophene (VI) were synthesized and used as substrates in biodegradation studies. The products of their aerobic metabolism by pure bacterial cultures were identified. In most cases, the long alkyl chains of these thiophenes were preferentially attacked and in pure cultures of alkane-degrading bacteria, the major metabolites that accumulated in the medium were 5-methyl-2-thiopheneacetic acid from (I), 5-methyl-2-thiophenecarboxylic acid from (II) and occasionally from (V), 5-butyl-2-thiophenecarboxylic acid from (III) and 5-ethyl-2-thiopheneacetic acid from (VI). These transformations are consistent with the metabolism of the alkyl side chains via the beta-oxidation pathway. In contrast, 5-(3,7-dimethyloctyl)-2-thiophenecarboxylic acid was produced from (IV). Because it was available in greatest supply, (I) was studied most thoroughly. It supported growth of the six n-alkanedegrading bacteria tested and (I) was degraded more quickly than pristane but not as quickly as nhexadecane in mixtures of these three compounds. In the presence of Prudhoe Bay crude oil and a mixed culture of petroleum-degrading bacteria, the acid metabolites from (I), (II) and (III) underwent further biotransformations to products that were not detected by the analytical methods used. The addition of n-hexadecane to the mixed culture of petroleum-degrading bacteria also enhanced the further biotransformations of the metabolites from (I).

Biodegradation of n -Alkylcycloalkanes and n -Alkylbenzenes via New Pathways in Alcanivorax sp. Strain MBIC 4326

“…In fungi (Beauveria, Penicillium, and Paecilomyces spp. ), both carboxylic acid and acetic acid derivatives accumulated from 2-n-dodecyltetrahydrothiophene (12). Similar phenomena have been observed in various microbial degradation processes of n-alkylcyclohexanes, n-alkylbenzenes, and nalkylbenzene sulfonic acids (3,11,20,23).…”

Microbial metabolism of some 2,5-substituted thiophenes

“…The microbial metabolism of six alkylthiophenes was investigated previously (Fedorak & Peakman 1992). The compounds studied had a methyl, ethyl or butyl group in the 2-position of the thiophene ring, and side chains of 10 to 20 carbon atoms in the 5-position.…”

“…With the exception of 2-(3,7-dimethyloctyl)-5-methylthiophene, the metabolites identified indicated that the long side chains were attacked by n-alkane-degrading bacteria. For example, 2-hexadecyl-5-methylthiophene was degraded to 5-methyl-2-thiophenecarboxylic acid and 5-methyl-2-thiopheneacetic acid that accumulated in cultures that contained no crude oil (Fedorak & Peakman 1992). However, these intermediates underwent further biotransformation to undetected metabolites if crude oil or n-hexadecane was added to the culture medium.…”

“…In our earlier studies (Fedorak & Peakman 1992), no metabolites of the thiophene carboxylic acids were detected by our routine solvent-extraction and gas chromatography (GC) method. We postulated that some of the dialkylthiophenes may undergo omegaoxidation, as is the case with pristane (Pirnik et al 1974) leading to dicarboxylic acids, or that the methyl groups of 5-methyl-2-thiophenecarboxylic acid and 5-methyl-2-thiopheneacetic acid may be oxidized to a carboxylic acid, producing a dicarboxylic acid.…”

“…We postulated that some of the dialkylthiophenes may undergo omegaoxidation, as is the case with pristane (Pirnik et al 1974) leading to dicarboxylic acids, or that the methyl groups of 5-methyl-2-thiophenecarboxylic acid and 5-methyl-2-thiopheneacetic acid may be oxidized to a carboxylic acid, producing a dicarboxylic acid. These dicarboxylic acids would be too polar to be solvent-extracted from the growth medium for GC analysis, and thus would not be detected using the methods outlined in the previous study (Fedorak & Peakman 1992). Evidence of methyl group oxidation was provided when a bacterial strain grown on n-tetradecane in the presence of 2-(3,7-dimethyloctyl)-5-methylthiophene yielded 5-(3,7-dimethyloctyl)-2-thiophenecarboxylic acid (Fedorak & Peakman 1992).…”