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...
During cassava starch production, large amounts of cyanoglycosides were released and hydrolysed by plant-borne enzymes, leading to cyanide concentrations in the wastewater as high as 200 mg/l. For anaerobic degradation of the cyanide during pre-acidification or single-step methane fermentation, anaerobic cultures were enriched from soil residues of cassava roots and sewage sludge. In a pre-acidification reactor this culture was able to remove up to 4 g potassium cyanide/l of wastewater at a hydraulic retention time (tHR) of 4 days, equivalent to a maximal cyanide space loading of 400 mg CN- 1(-1) day-1. The residual cyanide concentration was 0.2-0.5 mg/l. Concentrated cell suspensions of the mixed culture formed ammonia and formate in almost equimolar amounts from cyanide. Little formamide was generated by chemical decay. A concentration of up to 100 mmol ammonia/l had no inhibitory effect on cyanide degradation. The optimal pH for cyanide degradation was 6-7.5, the optimal temperature 25-37 degrees C. At a pH of 5 or lower, cyanide accumulated in the reactor and pre-acidification failed. The minimal tHR for continuous cyanide removal was 1.5 days. The enriched mixed culture was also able to degrade cyanide in purely mineralic wastewater from metal deburring, either in a pre-acidification reactor with a two-step process or in a one-step methanogenic reactor. It was necessary to supplement the wastewater with a carbon source (e.g. starch) to keep the population active enough to cope with any possible inhibiting effect of cyanide.
During the process of producing cassava starch from Manihot esculenta roots, large amounts of cyanoglycosides were released, which rapidly decayed to CN- following enzymatic hydrolysis. Depending on the varying cyanoglycoside content of the cassava varieties, the cyanide concentration in the wastewater was as high as 200 mg/l. To simulate anaerobic stabilization, a wastewater with a chemical oxygen demand (COD) of about 20 g/l was prepared from cassava roots and was fermented in a fixed-bed methanogenic reactor. The start-up phase for a 99% degradation of low concentrations of cyanide (10 mg/l) required about 6 months. After establishment of the biofilm, a cyanide concentration of up to 150 mg CN-/l in the fresh wastewater was degraded during anaerobic treatment at a hydraulic retention time of 3 days. All nitrogen from the degraded cyanide was converted to organic nitrogen by the biomass of the effluent. The cyanide-degrading biocoenosis of the anaerobic reactor could tolerate shock concentrations of cyanide up to 240 mg CN-/l for a short time. Up to 5 mmol/l NH4Cl (i.e. 70 mg N/l = 265 mg NH4Cl/l) in the fresh wastewater did not affect cyanide degradation. The bleaching agent sulphite, however, had a negative effect on COD and cyanide removal. For anaerobic treatment, the maximum COD space loading was 12 g l-1 day-1, equivalent to a hydraulic retention time of 1.8 days. The COD removal efficiency was around 90%. The maximum permanent cyanide space loading was 50 mg CN- l-1 day-1, with tolerable shock loadings up to 75 mg CN- l-1 day-1. Under steady-state conditions, the cyanide concentration of the effluent was lower than 0.5 mg/l.
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