BACTERIAL TRANSFORMATIONS OF NAPHTHOTHIOPHENES

Naphthothiophenes are minor components of fossil fuels, and they can e nter the environment from oil spills. Naphtho [2,1-b] thiophene, napht ho[2,3-b] thiophene, and 1-methylnaphtho [2,1-b]thiophene were synthes ized and used in biodegradation studies with 1-methylnaphthalene (1-MN )-degrading Pseudomonas strains W1, F, and BT1. Cultures were incubate d with one of the naphthothiophenes with or without 1-MNI acidified, a nd extracted with CH2Cl2. The extracts were analyzed by gas chromatogr aphy with flame photometric and mass detectors to characterize sulfur- containing metabolites and with an atomic emission detector for quanti fication. 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]t hiophene, which was more resistant to biodegradation than the [2,1-b] isomer. Two metabolites of naphtho [2,1-b]thiophene were purified, ana lyzed by H-1 nuclear magnetic resonance spectroscopy, and found to be 4-hydroxybenzothiophene-5-carboxylic acid (metabolite I) and 5-hydroxy benzothiophene-4-carboxylic acid (metabolite II). In cultures of strai n 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]thiop hene. 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. App roximately 70% of the 1-methylnaphtho [2,1-b]thiophene added to cultur es of strain W1 with 1-MN was recovered as 4-hydroxy-3-methylbenzothio phene-5-carboxylic acid, the 3-methyl analog of metabolite I. The meth yl substitution hindered further metabolism of 3-methyl-metabolite I e ven in the presence of 1-MN. Cometabolism of naphtho[2,3-b] thiophene yielded two products that were tentatively identified as 5-hydroxybenz othiophene-6-carboxylic and 6-hydroxybenzothiophene-5-carboxylic acids .