The biodegradation of 2,4,6-trichlorophenol (2,4,6-TCP) by Phanerochaete chrysosporium was studied in batch systems. In experiments with mycelial suspension, the degradation of 2,4,6-TCP was found to occur in the absence of ligninase. Chloride ion was recovered in nearly stoichiometric amounts at the end of the process. The microorganism did not retain its degradation ability for more than 6 days under substrate-deficient conditions. Neither the mycelium nor the extracellular protein alone could degrade 2,4,6-TCP; both were required for complete degradation to occur. In experiments in which 2,4,6-TCP was exposed to the culture supernatant separated from its mycelium, negligible degradation was obtained and no chloride ion was recovered. No degradation was observed even when the supernatant was supplemented with hydrogen peroxide as a possible cosubstrate. In experiments performed with washed mycelium separated from its supernatant, no degradation took place until the mycelium released additional extracellular protein 5 to 6 h into the incubation. Additions of washed mycelium separated from its supernatant to active cultures also produced an increase in the rate of degradation in correspondence with the protein release. The protein release was independent of the presence of 2,4,6-TCP. The addition of cycloheximide to inhibit the synthesis of de novo proteins completely suppressed the release of protein by the mycelium and resulted in no 2,4,6-TCP degradation. Additions of culture supernatants containing a high concentration of extracellular protein to active cultures produced an increase in the rate of 2,4,6-TCP degradation. The results of this work indicate that the concentration of extracellular protein is the limiting factor in 2,4,6-TCP degradation but that no degradation can take place unless the mycelium is simultaneously present. This can be interpreted as an indication that sequential steps requiring both extracellular and cellular enzymes are involved in the degradation of 2,4,6-TCP by P. chrysosporum.
The biodegradation of 2,4,6-trichlorophenol and 2,4,5-trichlorophenol by the white rot fungus Phanerochaete chrysosporium was studied in batch and continuous reactor systems. Experiments were conducted in shake flasks as well as in packed-bed reactors in which the fungus was immobilized. The degradation rates in the packed-bed reactors were found to be two orders of magnitude greater than those obtained in the shake flasks in which the fungus was just suspended. The degradation rate was found to be influenced by the concentrations of the carbon and nitrogen sources, pH, and fluid shear stress. Optimal ranges of these parameters to maximize biodegradation were determined. A mathematical model was developed in which the degradation process was assumed to consist of two sequential reaction steps, the first catalyzed by an extracellular enzyme system and the second requiring the presence of the mycelium. The deactivation of the extracellular enzyme system was also accounted for in the model. The Michaelis-Menten and the enzyme deactivation parameters were determined independently. Good agreement between the experimental data and the results produced by the regression was found.
Nitroglycerin or glycerol trinitrate (GTN) is an energetic and toxic substance with a wide range of military and pharmaceutical applications. Studies conducted with activated sludge showed that GTN is amenable to aerobic degradation only in the presence of a primary carbon source, such as glucose.Kinetic experiments indicated that GTN is an inhibitory substrate whose presence during biodegradation, reduces substantially the microbial yield and the apparent maximum specific growth rate coefficient of primary substrates. However, in the 547 BHAUMIK ET AL. range of concentrations tested (50 to 200 mg/L of GTN) its inhibitory effects are reversible. The biodegradation mechanism proceeds via a set of successive denitration reactions to form isomers of glycerol dinitrate (1,2-GDN and 1,3-GDN) and glycerol mononitrate (1-GMN and 2-GMN), which are subsequently degraded. Significant regioselectivity was observed during denitration of GTN and 1,2-GDN favoring production of 1,3-GDN and 1-GMN. The rates of degradation of the metabolic products of GTN were slower at each denitration step with 2-GMN exhibiting the lowest denitration rate. Aerobic GTN degradation ceased upon exhaustion of the primary substrate. Although, cosubstrate requirements during aerobic bioconversion of GTN were relatively high, in field applications the need for addition of external carbon sources will be minimal since GTN waste streams usually contain high amounts of BOD.
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