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Abstract
Granules of expanded clay ("Lecaton") serving as a mineral filter bed in a groundwater purification plant (Lübeck, Metallhüttengelände) were investigated for the presence of mesophilic freshwater microorganisms able to degrade monomethylated naphthalenes under oxygen- and sulfate-reducing conditions. Microorganisms inhabiting the granules readily degraded 1-methylnaphthalene and 2-methylnaphthalene in the presence of oxygen. An enrichment culture of sulfate-reducing bacteria was obtained which grew on 2-methylnaphthalene but not on 1-methylnaphthalene. The enriched bacteria were sensitive toward high concentrations of sulfide and 2-methylnaphthalene in the medium. Naphthyl-2-methylsuccinate and 2-naphthoate were major metabolites that accumulated in cells during growth of the enrichment culture. This finding proposed that the initial reactions of 2-methylnaphthalene metabolism included addition of fumarate to the methyl group of the compound and further degradation to 2-naphthoate, analogous to toluene metabolism under anoxic conditions. However, the addition reaction was specific for 2-methylnaphthalene because none of the bacteria present in the enrichment culture was able to grow on toluene. 2-Methylnaphthalene might be degraded through cooperation of aerobic and sulfate-reducing bacteria on the basis of 2-naphthoate production and its utilization, respectively.