Biodegradation of ortho-cresol by a mixed culture of nitrate-reducing bacteria growing on toluene.

A mixed culture of nitrate-reducing bacteria degraded o-cresol in the presence of toulene as a primary growth substrate. No degradation of o-cresol was observed in the absence of toluene or when the culture grew on p-cresol and 2,4-dimethylphenol. In batch cultures, the degradation of o-cresol started after toluene was degraded to below 0.5 to 1.0 mg/liter but continued only for about 3 to 5 days after the depletion of toluene since the culture had a limited capacity for o-cresol degradation once toluene was depleted. The total amount of o-cresol degraded was proportional to the amount of toluene metabolized, with an average yield of 0.47 mg of o-cresol degraded per mg of toluene metabolized. Experiments with [ring-U-14C]o-cresol indicated that about 73% of the carbon from degraded o-cresol was mineralized to CO2 and about 23% was assimilated into biomass after the transient accumulation of unidentified water-soluble intermediates. A mathematical model based on a simplified Monod equation is used to describe the kinetics of o-cresol degradation. In this model, the biomass activity toward o-cresol is assumed to decay according to first-order kinetics once toluene is depleted. On the basis of nonlinear regression of the data, the maximum specific rate of o-cresol degradation was estimated to be 0.4 mg of o-cresol per mg of biomass protein per h, and the first-order decay constant for o-cresol-degrading biomass activity was estimated to be 0.15 h-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular and kinetic characterization of mixed cultures degrading natural and synthetic estrogens

The biodegradation of estradiol (E2), estrone (E1), and ethinylestradiol (EE2) was investigated using mixed bacterial cultures enriched from activated sludge. Enrichments were carried out on E2 or EE2 in batch conditions with acetonitrile as additional carbon source. Degradation experiments were performed both using hormones as sole carbon source or with an additional source. The hormones were completely degraded by these cultures. Estradiol was rapidly converted to E1 within 24 h. Thereafter, E1 degradation began, displaying a lag phase ranging from 3 to 4 days. Estrone depletion took from 48 h to more than 6 days, depending on the culture conditions. For EE2 degradation, when it was the sole carbon source, the lag phase and the time required for its complete removal (7 and 15 days, respectively) were shorter that in cultures with a supplementary carbon source. The specific degradation rates observed for E2 both with and without an additional carbon source were similar. By contrast, the specific degradation rates for E1 and EE2 were, respectively, seven and 20 times faster when these hormones were supplied as the sole carbon source. The bacterial community structure of each culture was characterized by molecular and cultural methods. The mixed cultures were made up of species belonging to Alcaligenes faecalis, Pusillimonas sp., Denitrobacter sp., and Brevundimonas diminuta or related to uncultured Bacteroidetes. The isolated strain B. diminuta achieved the conversion of E2 to E1.     

Pilot trials of the microbial degradation of Christos-Bitas water in oil emulsion (chocolate mousse) and BP llandarcy gas oil using venturi aeration

Oil residues arising from the Christos-Bitas spillage were found to contain 28% of oil extractable by carbon tetrachloride; the remainder consisted of water and undefined solids. Christos-Bitas mousse was added to 1.18 m(3) liquor inoculated with oil-contaminated marine mud, and aerated with a 1.5-hp vortex pump and venturi nozzle (12.5 mm) in a cylindrical tank. After 70 days, oil degradation reached 7 mg oil/L/h. About 98% of the solvent extractable oil added was degraded over 83 days. Analysis of oil residues harvested at the end of this experiment showed that there was a decreasing trend in percent degradation in the following order: aromatics > saturates > heterocyclics > asphalts. No less than 94% of any fraction analysed was degraded.In the second pilot trial, oil degradation was carried out in a cylindrical jacket tank containing 6.82 m(3) liquor inoculated with oil-contaminated marine mud from Penarth, South Wales, UK, together with pure cultures derived from the same source, and aerated with a 7.5-hp vortex pump and venturi nozzle (18 mm diameter). Mixing of the oil was inhomogeneous for the first 100-110 days. The overall degree of substrate dispersion and total oil balance was determined by sampling at different depths. Degradation by the mixed culture was achieved at the rate of 164 mg oil/L/h. After 224 days, this was equivalent to 9.6 x 10(3)/kg(-1)/yr;(214 kg/wk) for 6.82 m(3) of liquor. The degradation rate continued to rise as the feed rate was increased by means of an automatic, timed pump. A lag phase of five to six months was necessary to allow the mixed population to build up to an exploitable level.     

Degradation of High Molecular Weight PAHs in Contaminated Soil by a Bacterial Consortium: Effects on Microtox and Mutagenicity Bioassays

Bioaugmentation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil was investigated using a mixed bacterial culture (community five) isolated from an abandoned industrial site. Community five was inoculated into contaminated soil containing a total PAH (two- to five-ring compounds) concentration of approximately 820 mg/kg soil. PAH degradation by the indigenous microbial population was restricted to the lower molecular weight compounds (naphthalene, acenaphthene, fluorene and phenanthrene) even with yeast extract addition: these compounds decreased by 14 to 37%, in soil hydrated to 50% water capacity, following 91 days of incubation at 24°C. Inoculation of community five into this PAH-contaminated soil resulted in significant decreases in the concentration of all PAHs over the incubation period: greater than 86% of naphthalene, acenaphthene, fluorene, and phenanthrene were degraded after 91 days, while anthracene, fluoranthene, and pyrene were degraded to lesser extents (51.7 to 57.6%). A lag period of 48 to 63 days was observed before the onset of benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene removal. However, significant decreases in the concentration of these compounds (32.6, 25.2, and 18.5%, respectively) were observed after 91 days. No significant decrease in the mutagenic potential of organic soil extracts (as measured by the Ames Test) was observed after incubation of the soil with the indigenous microflora; however, the Microtox toxicity of aqueous soil extracts was reduced sevenfold. In contrast, extracts from contaminated soil inoculated with community five underwent a 43% decrease in mutagenic potential and the toxicity was reduced 170-fold after 91 days incubation. These observations suggest that community five could be utilised for the detoxification of PAH-contaminated soil.     

Isolation and Characterization of a Pseudomonas Oleovorans Degrading the Chloroacetamide Herbicide Acetochlor

To date, no pure bacterial cultures that could degrade acetochlor have been described. In this study, one strain of microorganism capable of degrading acetochlor, designated as LCa2, was isolated from acetochlor-contaminated soil. The strain LCa2 is Pseudomonas oleovorans according to the criteria of Bergey’s manual of determinative bacteriology and sequence analysis of the partial 16S rRNA gene. Optimum growth temperature and pH were 35 °C and 8.0, respectively. The strain could degrade 98.03% of acetochlor treated at a concentration of 7.6 mg l⁻¹ after 7 days of incubation and could tolerate 200 mg l⁻¹ of acetochlor. When the acetochlor concentration became higher, the degradation cycle became longer. The acetochlor biodegradation products were identified by GC–MS based on mass spectral data and fragmentation patterns. The main plausible degradative pathways involved dechlorination, hydroxylation, N-dealkylation, C-dealkylation and dehydrogenation.     

一株乙草胺降解菌的分离及其降解特性研究

【目的】分离获得一株能有效降解乙草胺的菌株,并研究其降解乙草胺的影响因素,为乙草胺生物修复提供微生物资源。【方法】通过富集培养和分离培养,从样品中筛选能以乙草胺为唯一碳氮源的菌株。通过划线培养获得单菌落,并采用革兰氏染色法和16S r RNA基因测序进行菌株的初步鉴定和系统分类。通过单因素试验研究初始乙草胺浓度、外加碳氮源对其降解乙草胺的影响,并基于正交设计进行优化。【结果】分离获得的一株菌为革兰氏阴性菌,初步确定为Pseudomonas sp.,能有效利用乙草胺进行生长。单因素试验证明在乙草胺初始浓度为10 mg/L时降解率最高;外加碳氮源能提高乙草胺降解率,其中葡萄糖和蛋白胨分别最为有效。正交设计表明在最优条件下,其对乙草胺降解率可以达到80.2%。【结论】菌株A-1能有效利用乙草胺进行生长,其降解乙草胺受多种因素影响。本研究将为利用进行该菌株进行乙草胺污染修复提供菌种资源。     

Biodegradation kinetics of 2,4-dichlorophenol by acclimated mixed cultures

The biodegradation kinetics of 2,4-dichlorophenol (2,4-DCP) by culture (Culture M) acclimated to mixture of 4-chlorophenol (4-CP) and 2,4-DCP and the culture (Culture 4) acclimated to 4-CP only were investigated in aerobic batch reactors. Also, pure strains isolated from mixed cultures were searched for their ability towards the biodegradation of 2,4-DCP. Culture 4 was able to completely degrade 2,4-DCP up to 80 mg/L within 30 h and removal efficiency dropped to 21% upon increasing initial concentration to 108.8 mg/L. When the Culture M was used, complete degradation of 2,4-DCP in the range of 12.5-104.4 mg/L was attained. A linear relationship between time required for complete degradation and initial 2,4-DCP concentrations was observed for both mixed cultures. It was observed that the Haldane equation can be used to predict specific degradation rate (SDR) (R(2)>0.99) as a function of initial 2,4-DCP concentrations and it adequately describes 2,4-DCP concentration profiles. Both of the mixed cultures settled well, which is important to maintain good removal efficiency for longer periods of time for real full-scale applications. Although the pure strains isolated from mixed cultures were found to have higher SDR of 2,4-DCP compared to mixed cultures, they did not settle well under quiescent conditions.     

Biotransformation of trichloroethene by pure bacterial cultures

From natural samples 11 isolates able to remove trichloroethene (CCl₂CHl) from an aqueousenvironment were obtained which were capable of cometabolic degradation of CCl₂CHCl by an enzyme system for phenol degradation. At an initial CCl₂CHCl concentration of 1 mg/L, the resting cells of particular cultures degraded 33–94% CCl₂CHCl during 1 d and their transformation capacity ranged from 0.3 to 3.1 mg CCl₂CHCl per g organic fraction. An analysis of a mixed phenol-fed culture with an excellent trichloroethene-degrading ability found a markedly minority isolate represented in the consortium to be responsible for this property. This culture degraded CCl₂CHCl even at a low inoculum concentration and attained a transformation capacity of 14.7 mg CCl₂CHCl per g. The increase in chloride concentration after degradation was quantitative when compared with the decrease in organically bound chlorine. The degree of CCl₂CHCl degradation was affected by Me₂S₂; this substance can significantly reduce the degrading ability of some tested cultures (>60%); however, it does not cause this inhibition with others.     

Biodegradation of Grape Cluster Stems and Ligninolytic Enzyme Production by Phanerochaete chrysosporium during Semi‐Solid‐State Cultivation

The degradation undergone by grape cluster stems (woody component of vine bagasse), an agroindustrial waste, was investigated during the semi‐solid‐state cultivation of Phanerochaete chrysosporium BKM‐F‐1767 (ATCC 24725). For this, the content of lignin, cellulose and hemicellulose in grape cluster stems was determined before and after the enzymatic process. It was found that about 20% of Klason lignin, 48% of hemicellulose and 5% of cellulose were degraded during the process, being the ligninolytic enzymes (manganese‐dependent peroxidase and lignin peroxidase) produced by such cultures responsible for the degradation of grape cluster stems. In parallel, semi‐solid‐state cultures of P. chrysosporium grown on an inert support (cubes of nylon sponge), which is not susceptible to undergoing degradation during the enzymatic process, were used as reference cultures. In addition, the in vivo decolourisation of a model dye, the polymeric dye Poly R‐478, by both grape cluster stem and nylon cultures was studied in order to assess their degradative ability. A percentage of biological decolourisation higher than 90% after four days of dye addition was obtained using nylon sponge cultures, whereas grape cluster stem cultures led to a decolourisation of around 70% after eight days of dye incubation. The lower percentage of dye degradation achieved by the cultures grown on grape cluster stems was due to the enzymes produced, which were not only employed in the decolourisation of the dye but also in the degradation of the support, as indicated by the data mentioned above.     

Removal of phenolic compounds from a petrochemical effluent with a methanogenic consortium.

A methanogenic consortium was used to degrade phenol and ortho- (o-) cresol from a specific effluent of a petrochemical refinery. This effluent did not meet the local environmental regulations for phenolic compounds (178 mg/L), oils and greases (61 mg/L), ammoniacal nitrogen (75 mg/L) or sulfides (3.2 mg/L). The consortium, which degrades phenol via its carboxylation to benzoic acid, was progressively adapted to the effluent. Despite the very high effluent toxicity (EC50 of 2% with Microtox), the adapted consortium degraded 97% of 156 mg/L phenol in the supplemented effluent after 13 days in batch cultures (serum bottle). The addition of proteose peptone to the effluent is essential for phenol degradation. o-cresol was also transformed but not meta- or para-cresols. A continuous flow fixed-film anaerobic bioreactor was developed with the consortium. Treating the effluent with the bioreactor reduced phenol and phenolic compounds concentrations by 97 and 83%, respectively, for a hydraulic residence time of 6 h. This treatment also reduced by about half the effluent toxicity. Oils and greases and ammoniacal nitrogen were not affected. Similar microbiological forms were observed in serum bottles and in the bioreactors with or without the petrochemical effluent. These results indicate that this methanogenic consortium can treat efficiently the phenolic compounds in this specific petrochemical effluent.     

Process development for degradation of phenol by Pseudomonas putida in hollow-fiber membrane bioreactors

The degradation of phenol (100-2800 mg/L) by cells Pseudomonas putida CCRC14365 in an extractive hollow-fiber membrane bioreactor (HFMBR) was studied, in which the polypropylene fibers were prewetted with ethanol. The effects of flow velocity, the concentrations of phenol, and the added dispersive agent tetrasodium pyrophosphate on phenol degradation and cell growth were examined. It was shown that about 10% of phenol was sorbed on the fibers at the beginning of the degradation process. The cells P. putida fully degraded 2000 mg/L of phenol within 73 h when the cells were immobilized and separated by the fibers. Even at a level of 2800 mg/L, phenol could be degraded more than 90% after 95-h operation. At low phenol levels (< 400 mg/L) where substrate inhibition was not severe, it was more advantageous to treat the solution in a suspended system. At higher phenol levels (> 1000 mg/L), however, such HFMBR-immobilized cells could degrade phenol to a tolerable concentration with weak substrate-inhibition effect, and the degradation that followed could be completed by suspended cultures due to their larger degradation rate. The process development in an HFMBR system was also discussed.     

Biochemical degradation pathway of reactive blue 13 by Candida rugopelliculosa HXL-2

A strain HXL-2 from a lab-scale sequence batch reactor (SBR) was identified as Candida rugopelliculosa based on its physiological, biochemical characteristics, and 26S rDNA D1/D2 gene phylogenetic analysis. About 90% of the 50 mg/L Reactive blue 13(RB13) was degraded in 48 h after inoculation with strain HXL-2. The optimum efficiency of pH on decolorization was obtained at pH 5.The optimum efficiency temperature of C. rugopelliculosa HXL-2 decolorization RB13 was obtained at 28 °C. The color removal efficiency was obtained at 80.3% when the feed concentration reached 2000 mg/L. We first detected naphthalene-like compound is produced as degradation intermediate after the cleavage of RB13 azo bond, detected 1-chloro-3-aniline- 2,4,6-triazine. We proposed degradation pathway of Reactive blue 13 by Candida sp and proved RB13 degradation pathway by Candida sp. has some difference from RB13 degradation pathway by Pseudomonas sp.     

The effect of concentration of phenols on their batch methanogenesis

The biodegradability of phenol and six other phenolic compounds (o-, m-, and p-cresol, 2-, 3-, and 4-ethylphenol) was examined in batch methanogenic cultures. The effect of concentration of these alkyl phenols on the anaerobic biodegradation of phenol was also evaluated. The inoculum used in this study was cultivated in a continuous flow laboratory fermenter with phenol as the primary substrate. Phenol, at initial concentrations as high to 1400 mg/L was completely degraded to methane and carbondioxide after 350 hours incubation. Complete degradation of m- and p-cresol was also observed while the ethylphenols and o-cresol were not significantly degraded.At initial concentrations exceeding 600 mg/L, phenol inhibited the phenol-degrading microorganisms but not the methanogens. At about 600 mg/L, cresols reduced the rate of phenol degradation to 50% of that observed in a control culture containing only 200 mg/L phenol. Ethylphenols were more inhibitory than cresols. Phenol degrading microorganisms were more susceptible to inhibition by cresols and ethylphenols than were the methanogens. The inhibitory effects of the three isomers of cresol and ethylphenol did not vary with the isomer but rather with the substituted functional group.     

Temperature effects and substrate interactions during the aerobic biotransformation of BTEX mixtures by toluene-enriched consortia and Rhodococcus rhodochrous

A microbial consortium derived from a gasoline-contaminated aquifer was enriched on toluene (T) in a chemostat at 20 degrees C and was found to degrade benzene (B), ethylbenzene (E), and xylenes (X). Studies conducted to determine the optimal temperature for microbial activity revealed that cell growth and toluene degradation were maximized at 35 degrees C. A consortium enriched at 35 degrees C exhibited increased degradation rates of benzene, toluene, ethylbenzene, and xylenes in single-substrate experiments; in BTEX mixtures, enhanced benzene, toluene, and xylene degradation rates were observed, but ethylbenzene degradation rates decreased. Substrate degradation patterns over a range of BTEX concentrations (0 to 80 mg/L) for individual aromatics were found to differ significantly from patterns for aromatics in mixtures. Individually, toluene was degraded fastest, followed by benzene, ethylbenzene, and the xylenes. In BTEX mixtures, degradation followed the order of ethylbenzene, toluene, and benzene, with the xylenes degraded last. A pure culture isolated from the 35 degrees C-enriched consortium was identified as Rhodococcus rhodochrous. This culture was shown to degrade each of the BTEX compounds, individually and in mixtures, following the same degradation patterns as the mixed cultures. Additionally, R. rhodochrous was shown to utilize benzene, toluene, and ethylbenzene as primary carbon and energy sources. Studies conducted with the 35 degrees C-enriched consortium and R. rhodochrous to evaluate potential substrate interactions caused by the concurrent presence of multiple BTEX compounds revealed a range of substrate interaction patterns including no interaction, stimulation, competitive inhibition, noncompetitive inhibition, and cometabolism. In the case of the consortium, benzene and toluene degradation rates were slightly enhanced by the presence of o-xylene, whereas the presence of toluene, benzene, or ethylbenzene had a negative effect on xylene degradation rates. Ethylbenzene was shown to be the most potent inhibitor of BTEX degradation by both the mixed and pure cultures. Attempted quantification of these inhibition effects in the case of the consortium suggested a mixture of competitive and noncompetitive inhibition kinetics. Benzene, toluene, and the xylenes had a negligible effect on the biodegradation of ethylbenzene by both cultures. Cometabolism of o-, m-, and p-xylene was shown to be a positive substrate interaction.     

16S rDNA-RFLP分析六氯苯好氧降解菌群的结构及其多样性

从某化工厂排水沟底泥中取样,经2个月的富集驯化得到六氯苯好氧降解菌群。通过测定该微生物菌群在降解六氯苯过程中累积耗氧量、微生物生长曲线及Cl-浓度的变化,证明在好氧条件下该微生物菌群能够以六氯苯为唯一碳源和能源生长。当培养温度为30℃,pH为7.0时,该菌群能在18d内将无机盐培养基中浓度为4.5mg/L的六氯苯降解55%以上,降解速率达到137.5μg/(L.d)。对降解菌群提取总DNA,选择性扩增细菌16S rDNA片段,建立克隆文库。通过限制性内切酶(限制性内切酶HaeⅢ和RsaⅠ)分析,得到9种不同的谱型,其中3种谱型是主要谱型。对主要谱型的克隆子测序,结果表明,它们分别与Alcaligenes和Azospirillum菌属相似性最高。该菌群在去除环境中难降解的有机氯污染物方面具有应用前景。     

乙草胺的微生物降解及其对土壤磷脂脂肪酸特性的影响

通过监测不同培养条件下（灭菌、加选择抑菌剂、未灭菌）土壤中乙草胺残留数量和培养期间微生物标识物磷脂脂肪酸（PLFAs）含量的变化,探讨了以田间推荐量施用乙草胺时,不同微生物群落对乙草胺降解的相对贡献以及乙草胺对黑土微生物群落结构的影响.结果表明：乙草胺易于被微生物降解,其中,细菌对乙草胺的降解作用显著大于真菌,而真菌对乙草胺有更强的耐受能力.施入乙草胺后,各磷脂脂肪酸数量发生了显著变化,C14∶0、C16∶0和C18∶0所指示的土壤微生物量均有所下降;细菌PLFAs数量在培养初期显著降低,而后与对照的差异显著减小,表明细菌活性随着乙草胺的降解有所恢复;在施用乙草胺后的整个培养过程中,土壤真菌PLFAs数量始终低于对照,暗示着乙草胺对真菌的抑制可能是长期而不可逆的.     

Biodegradation of Trichloroethylene in Continuous-Recycle Expanded-Bed Bioreactors

Experimental bioreactors operated as recirculated closed systems were inoculated with bacterial cultures that utilized methane, propane, and tryptone-yeast extract as aerobic carbon and energy sources and degraded trichloroethylene (TCE). Up to 95% removal of TCE was observed after 5 days of incubation. Uninoculated bioreactors inhibited with 0.5% Formalin and 0.2% sodium azide retained greater than 95% of their TCE after 20 days. Each bioreactor consisted of an expanded-bed column through which the liquid phase was recirculated and a gas recharge column which allowed direct headspace sampling. Pulses of TCE (20 mg/liter) were added to bioreactors, and gas chromatography was used to monitor TCE, propane, methane, and carbon dioxide. Pulsed feeding of methane and propane with air resulted in 1 mol of TCE degraded per 55 mol of substrate utilized. Perturbation studies revealed that pH shifts from 7.2 to 7.5 decreased TCE degradation by 85%. The bioreactors recovered to baseline activities within 1 day after the pH returned to neutrality.     

Isolation and characterization of ethylbenzene degrading <Emphasis Type="Italic">Pseudomonas putida</Emphasis> E41

Pseudomonas putida E41 was isolated from oil-contaminated soil and showed its ability to grow on ethyl-benzene as the sole carbon and energy source. Moreover, P. putida E41 show the activity of biodegradation of ethylbenzene in the batch culture. E41 showed high efficiency of biodegradation of ethylbenzene with the optimum conditions (a cell concentration of 0.1 g wet cell weight/L, pH 7.0, 25°C, and ethylbenzene concentration of 50 mg/L) from the results of the batch culture. The maximum degradation rate and specific growth rate (μ_max) under the optimum conditions were 0.19+0.03 mg/mg-DCW (Dry Cell Weight)/h and 0.87+0.13 h⁻¹, respectively. Benzene, toluene and ethylbenzene were degraded when these compounds were provided together; however, xylene isomers persisted during degradation by P. putida E41. When using a bioreactor batch system with a binary culture with P. putida BJ10, which was isolated previously in our lab, the degradation rate for benzene and toluene was improved in BTE mixed medium (each initial concentration: 50 mg/L). Almost all of the BTE was degraded within 4 h and 70–80% of m-, p-, and o-xylenes within 11 h in a BTEX mixture (initial concentration: 50 mg/L each). In summary, we found a valuable new strain of P. putida, determined the optimal degradation conditions for this isolate and tested a mixed culture of E41 and BJ10 for its ability to degrade a common sample of mixed contaminants containing benzene, toluene, and xylene.     

The degradation of the herbicide bromoxynil and its impact on bacterial diversity in a top soil

Aims: To study how repeated applications of an herbicide bromoxynil to a soil, mimicking the regime used in the field, affected the degradation of the compound and whether such affects were reflected by changes in the indigenous bacterial community present. Methods and Results: Bromoxynil degradation was monitored in soil microcosms using HPLC. Its impact on the bacterial community was determined using denaturing gradient gel electrophoresis (DGGE) and quantitative PCR of five bacterial taxa (Pseudomonads, Actinobacteria, α‐Proteobacteria, Acidobacteria and nitrifying bacteria). Three applications of 10 mg kg^?1 of bromoxynil at 28‐day intervals resulted in rapid degradation, the time for removal of 50% of the compound decreasing from 6·4 days on the first application to 4·9 days by the third. Bacterial population profiles showed significant similarity throughout the experiment. With the addition of 50 mg kg^?1 bromoxynil to soil, the degradation was preceded by a lag phase and the time for 50% of the compound to be degraded increased from 7 days to 28 days by the third application. The bacterial population showed significant differences 7 days after the final application of bromoxynil that correlated with an inhibition of degradation during the same period. Conclusions: These analyses highlighted that the addition of bromoxynil gave rise to significant shifts in the community diversity and its structure as measured by four abundant taxa, when compared with the control microcosm. These changes persisted even after bromoxynil had been degraded. Significance and Impact of the Study: Here we show that bromoxynil can exert an inhibitory effect on the bacterial population that results in decreased rates of degradation and increased persistence of the compound. In addition, we demonstrate that molecular approaches can identify statistically significant changes in microbial communities that occur in conjunction with changes in the rate of degradation of the compound in the soil.     

Biodegradation of TNT (2,4,6-trinitrotoluene) by Phanerochaete chrysosporium

Extensive biodegradation of TNT (2,4,6-trinitrotoluene) by the white rot fungus Phanerochaete chrysosporium was observed. At an initial concentration of 1.3 mg/liter, 35.4 +/- 3.6% of the [14C]TNT was degraded to 14CO2 in 18 days. The addition of glucose 12 days after the addition of TNT did not stimulate mineralization, and, after 18 days of incubation with TNT only, about 3.3% of the initial TNT could be recovered. Mineralization of [14C]TNT adsorbed on soil was also examined. Ground corncobs served as the nutrient for slow but sustained degradation of [14C]TNT to 14CO2 such that 6.3 +/- 0.6% of the [14C]TNT initially present was converted to 14CO2 during the 30-day incubation period. Mass balance analysis of liquid cultures and of soil-corncob cultures revealed that polar [14C]TNT metabolites are formed in both systems, and high-performance liquid chromatography analyses revealed that less than 5% of the radioactivity remained as undegraded [14C]TNT following incubation with the fungus in soil or liquid cultures. When the concentration of TNT in cultures (both liquid and soil) was adjusted to contamination levels that might be found in the environment, i.e., 10,000 mg/kg in soil and 100 mg/liter in water, mineralization studies showed that 18.4 +/- 2.9% and 19.6 +/- 3.5% of the initial TNT was converted to 14CO2 in 90 days in soil and liquid cultures, respectively. In both cases (90 days in water at 100 mg/liter and in soil at 10,000 mg/kg) approximately 85% of the TNT was degraded. These results suggest that this fungus may be useful for the decontamination of sites in the environment contaminated with TNT.