An organism capable to grow aerobically on tetrahydrofuran as sole source of carbon and energy was isolated from a waste water treatment plant. The organism designated as strain K1 was identified as Pseudonocardia sp. by chemotaxonomic and morphological characteristics as well as analysis of the gene encoding the 16S rRNA. The highest binary sequence similarity value of 99.0% was obtained to Pseudonocardia sulfidoxydans and Pseudonocardia hydrocarbonoxydans. Optimal growth with a doubling time of 14 h was observed at a tetrahydrofuran concentration of 20 mM and pH 7.0 at 28 degrees C. Under these conditions the substrate was completely degraded within 72 h. In situ concentrations of up to 60 mM were tolerated by the organism without a significantly increased doubling time. The strain also grew on diethyl ether, polyethylene glycol and on gamma-butyrolactone and 4-hydroxybutyrate - two potential intermediates in tetrahydrofuran degradation - as sole carbon and energy source.