The use of a solid adsorber resin for enrichment of bacteria with toxic substrates and to identify metabolites: degradation of naphthalene, o-, and m-xylene by sulfate-reducing bacteria

Anaerobic sulfate-reducing bacteria were enriched from contaminated aquifer samples with naphthalene, o-, and m-xylene as sole carbon and energy sourc e in the presence of Amberlite-XAD7, a solid adsorber resin. XAD7 served as a substrate reservoir maintaining a constantly low substrate concentration in the culture medium. In equilibration experiments with XAD7, the aromati c hydrocarbons needed up to 5 days to achieve equilibrium between the water and the XAD7 phase. The equilibrium concentration was directly correlated with the amount of added substrate and XAD7. In the enrichments presented h ere, XAD7 and aromatic hydrocarbons were adjusted to maintain substrate con centrations of 100 muM m-, or o-xylene, or 50 muM naphthalene. After five s ubsequent transfers. the three cultures were able to grow with higher subst rate concentrations in the absence of XAD7 although they grew best with low er hydrocarbon concentrations. Two new xylene-degrading cultures were obtai ned that could not utilise toluene as carbon source. O-xylene was degraded anaerobically by a culture, which could also oxidise in-xylene but not p-xy lene. Eighty-three percent of the electrons from o-xylene oxidation were re covered in the produced sulfide, indicating a complete oxidation to CO2. An other sulfate-reducing enrichment culture oxidised m-xylene completely to C O2 but not o-, or p-xylene. A naphthalene-degrading sulfate-reducing enrich ment culture oxidised naphthalene completely to CO2. Metabolites of naphtha lene degradation were recovered from the XAD7 phase and subjected to GC/Ms analysis. Besides the metabolites 2-naphthoic acid and decahydro-2-naphthoi c acid which were identified by the mass spectrum and coelution with chemic ally synthesised reference compounds, the reduced 2-naphthoic acid derivati ves 5,6,7,8-tetrahydro-2-naphthoic acid and octahydro-2-naphthoic acid were tentatively identified by their mass spectra. Cultivation of bacterial cul tures in the presence of XAD7 and subsequent derivatisation and extraction of metabolites directly from the solid XAD7 resin provides a new method for the isolation of sensitive bacteria and identification of metabolites. (C) 2001 Published by Elsevier Science B.V.