An acetone-degrading, nitrate-reducing, coccoid to rod-shaped bacterium, strain L1, was isolated from soil on the site of a natural gas company. Cells of the logarithmic growth phase reacted gram positive, while those of the stationary growth phase were gram negative. Single organisms were 0.4 to 0.5 by 0.9 to 1.5 pm in size, nonmotile, and non-spore forming and had poly-P-hydroxybutyrate inclusions. The doubling time of strain L1 on acetone-C0,-nitrate at the optimal pH of 7 to 8 and the optimal temperature of 30 to 37°C was 12 h. More than 0.2% NaCl or 10 mM thiosulfate inhibited growth. For oxygen or nitrate respiration, acetone and a few organic chemicals were utilized as carbon sources whereas many others could not be used (for details, see Results). Bicarbonate (or CO,) was essential for growth on acetone but not for growth on acetoacetate. The growth yields for acetone-CO, and acetoacetate were 28.3 and 27.3 g/mol, respectively. With acetone as the carbon source, poly-P-hydroxybutyrate accounted for up to 40% of the cellular dry weight. The DNA of strain L1 had a G+C content of 68.5 mol% (as determined by high-performance liquid chromatography of nucleotides) or 70 mol% (as determined by the T, method). The sequence of the gene coding for the 16s rRNA led to the classification of strain L1 in the paracoccus group of the alpha subclass of the Proteobucteriu. The new isolate is named Paracoccus solventivuruns sp. nov. DSM 6637.Acetone is a fermentation product of fungi (15), clostridia (see, for example, reference 43), and several other bacteria (6, 35,36,51,57,58). It is also excreted into the environment in ripening apples as a bioconversion product derived from p pvate. Commercially, acetone is produced from isopropanol, cumene, or propane to serve as a solvent for resins, fats, oil, plastics, waxes, etc. (30). Acetone may therefore occur in many ecosystems as a naturally produced substance or as an industrial pollutant. It is, however, not accumulating because of its degradability by aerobic (see, e.g., references 25 and 27) and anaerobic (see, e.g., references 28, 36, and 38) bacteria. Because of its biological degradability in the presence or absence of oxygen, it is an especially suitable, nontoxic elutant for extraction of polycyclic aromatic hydrocarbons (PAHs) from contaminated soil for bioremediation. After extraction, the acetone-PAH solution can be easily separated by evaporation or distillation of the solvent. The acetone residue in the soil is harmless because of its rapid biological degradation. In an attempt to study PAH degradation in contaminated soil Samples, PAHs were extracted with acetone. In the first enrichments, nitrate-reducing, acetone-degrading bacteria were obtained. From these enrichments, a new acetone-degrading organism, strain L1, was isolated and subsequently characterized in detail.MATERIALS AND METHODS Sources of organisms. Strain L1 was isolated from a soil sample taken at a depth of 1 m at the site of a defunct natural gas company. (2) and dispensed in an anaerobic c...