Naphthalene Degradation and Incorporation of Naphthalene-Derived Carbon into Biomass by the Thermophile Bacillus thermoleovorans

Abstract

The thermophilic aerobic bacterium Bacillus thermoleovorans Hamburg 2 grows at 60°C on naphthalene as the sole source of carbon and energy. In batch cultures, an effective substrate degradation was observed. The carbon balance, including naphthalene, metabolites, biomass, and CO 2 , was determined by the application of [1-13 C]naphthalene. The incorporation of naphthalene-derived carbon into the bulk biomass as well as into specified biomass fractions such as fatty acids and amino acids was confirmed by coupled gas chromatographymass spectrometry (GC-MS) and isotope analyses. Metabolites were characterized by GC-MS; the established structures allow tracing the degradation pathway under thermophilic conditions. Apart from typical metabolites of naphthalene degradation known from mesophiles, intermediates such as 2,3-dihydroxynaphthalene, 2-carboxycinnamic acid, and phthalic and benzoic acid were identified for the pathway of this bacterium. These compounds indicate that naphthalene degradation by the thermophilic B. thermoleovorans differs from the known pathways found for mesophilic bacteria.The naphthalene metabolism of mesophilic microorganisms under aerobic conditions has been intensely investigated, and detailed information has been presented on degradation rates, metabolic pathways, and the involved enzymes (7,8,11,25). In contrast, little is known about the metabolism of naphthalene or other polycyclic aromatic hydrocarbons (PAH) by thermophilic bacteria. Several studies on the growth of thermophilic microorganisms on aromatic compounds such as benzoic acid, cresols, or phenols have been carried out; however, respective degradation pathways are largely unresearched (1,4,19,20). The degradation of xenobiotics by thermophilic microorganisms provides crucial advantages compared to mesophilic organisms, especially when they are applied in biotechnological processes. Limited bioavailability as a result of the low water solubility of hydrophobic contaminants may be overcome due to a higher water solubility at elevated temperatures. The water solubility of naphthalene, for example, rises from 30 mg liter Ϫ1 at 20°C to 130 mg liter Ϫ1 at 60°C (26). Moreover, diffusion rates increase at higher temperatures with an additional positive impact on bioavailability.The bacteria applied in this degradation study were isolated from a compost consisting of wooden ties treated with lignite tar. They were able to utilize naphthalene as a sole source of carbon and energy. Stable isotope labeled [1-13 C]naphthalene was used as a model contaminant. The fate of naphthalene was traced by means of the technique of 13 C isotope analysis, which has been successfully applied to trace metabolic pathways (3,18,22). Stable isotope labeling enabled us to trace quantitatively the transformation of the xenobiotic carbon into specific fractions such as CO 2 , biomass, and metabolites. Moreover, the incorporation of the xenobiotic carbon into the bacterial fatty and amino acid fraction was determined on a molecular level. We describe here str...

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Degradation of naphthalene by thermophilic bacteria via a pathway, through protocatechuic acid

“…Four compounds (o-phthalic acid, 2-naphthol, 1-naphthol and protocatechuic acid) were detected directly ( Two metabolites of naphthalene degradation were identified as 1-naphthol and 2-naphthol ( Table 1), which have been described as intermediates of naphthalene degradation by B. cereus [29] and B. thermoleovorans [9]. Monohydroxylated naphthalenes could be intermediate compounds, but also a side reaction, because most of bacterial naphthalene cleavage reactions occur at the 1,2-position coursed by dioxygen- ation and dehydrogenation reactions [27].…”

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Meiofauna reduces bacterial mineralization of naphthalene in marine sediment

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