Identification of pyrene‐degradation pathways: Bench‐scale studies using Pseudomonas fluorescens 29L

This article summarizes the bench‐scale studies to identify pyrene‐degradation pathways using an environmental microbial isolate, Pseudomonas fluorescens 29L. Strain 29L was grown on 50 mg of pyrene per liter of mineral medium. At a pyrene biodegradation rate of 14.7 mg/L of medium/day, 82.38 percent of pyrene was degraded in six days. Naphthalene and phenanthrene accounted for 1.09 percent and 3.69 percent, respectively, of the carbon mass from pyrene in the late log phase. Substituted benzene compounds accounted for 26.10 percent of the carbon mass from pyrene in the late log phase. In the stationary phase, carboxylic acids accounted for 10.44 percent of the carbon mass from pyrene. Strain 29L mutants were used for enzyme assays. Pyrene is oxidized by monoxygenases and dioxygenases, and the oxidized ring is cleaved. These enzymes were induced in the presence of pyrene and their activities peaked in the late log phase. No gentisate 1,2‐dioxygenase activity was detected in Strain 29L wild type (WT), whereas mutant M15 did not show any catechol 2,3‐dioxygenase activity. This indicates the possibility of multiple branchings in the pyrene‐biodegradation pathways. In conclusion, multiple degradative pathways are operating concurrently in this strain. The study shows the versatility of Pseudomonas fluorescens Strain 29L for pyrene degradation. It also emphasizes the need to study pyrene‐degradation pathways in other microorganisms so as to enhance the bioremediation potential for the in situ treatment of pyrene‐contaminated sites. © 2008 Wiley Periodicals, Inc.     

Literature overview: Microbial metabolism of high molecular weight polycyclic aromatic hydrocarbons

High molecular weight polycyclic aromatic hydrocarbons (HMW PAHs) increase in hydrophobicity with increases in their molecular weight and ring angularity. Microbial strategies to deal with PAH hydrophobicity include biofilm formation, enzyme induction, and biosurfactants, the effect of which is variable on PAH metabolism depending on the surfactant type and concentration, substrate, and microbial strain(s). Aerobic HMW PAH metabolism proceeds via mineralization, partial degradation, and cometabolic transformations. Generally, bacteria and nonlignolytic fungi metabolize PAHs via initial PAH ring oxidation by dioxygenases to form cis‐dihydrodiols, which are transformed to catechol compounds by dehydrogenases and other mono‐ and dioxygenases to substituted catechol and noncatechol compounds, all ortho‐ or metacleaved and further oxidized to simpler compounds. However, lignolytic fungi form quinones and acids to CO₂. This review discusses the pathways for HMW PAH microbial metabolism. © 2008 Wiley Periodicals, Inc.     

Potential of immobilized bitter gourd (Momordica charantia) peroxidases in the decolorization and removal of textile dyes from polluted wastewater and dyeing effluent

Immobilized peroxidases from Momordica charantia were highly effective in decolorizing reactive textile dyes compared to its soluble counterpart. Dye solutions, 50-200 mg/l, were treated with soluble and immobilized bitter gourd peroxidases (specific activity of 99.0 EU per mg protein). The decolorization of dyes with soluble and immobilized enzyme was maximum in the range of pH 3.0-4.0. The effect of different temperatures on the dye decolorization was monitored and it was observed that all the dyes were maximally decolorized at 40 degrees C. In order to examine the operational stability of the immobilized preparation, the enzyme was repeatedly exploited for the decolorization of the dyes from fresh batch of dye solutions. Even after 10 cycles in each case the immobilized preparation retained nearly 50% of the initial enzyme activity. The immobilized enzyme exhibited more than 90% of the original activity while the soluble enzyme lost 33% of the initial activity when stored for 40 d at room temperature. Mixtures of three, four and eight dyes were prepared and treated with soluble and immobilized bitter gourd peroxidase. Each mixture was decolorized by more than 80% when treated with immobilized enzyme. Dyeing effluent collected from local dyers was treated with both types of enzyme preparations. Immobilized enzyme was capable of removing remarkably high concentration of color from the effluent. TOC content of soluble and immobilized enzyme treated individual dyes, mixture of dyes and dyeing effluent was determined and it was observed that higher TOC was removed after treatment with immobilized enzyme.     

Application of the SO4(2-)/Se tracer technique to study SO2 oxidation in cloud and fog on a time scale of minutes

We have demonstrated the use of Se as a tracer to quantitatively determine in situ SO4(2-) production from SO2 oxidation in clouds and fogs. Until now, it has not been possible to study the kinetics of SO2 oxidation because the aerosol sampling interval for Se determination was limited to 2 h or longer. Here we report results of 5-min aerosol measurements carried out at Lahore, Pakistan, during January 9-11, 2001, using new methodology for Se analysis coupled with hydride generation and ICP-MS detection. These improvements will enable the tracer technique to determine in situ SO4(2-) production in clouds and fogs on a time scale of several minutes and possibly 1 min. The method may prove useful for kinetic studies of in-cloud SO2 oxidation and in the study of other phenomena such as atmospheric mixing, cloud drop lifetimes, and aerosol formation that occur on the time scale of a few minutes.     

Catalyzed degradation of disperse dyes by calcium alginate-pectin entrapped bitter gourd （Momordica charantia） peroxidase

Calcium-alginate pectin entrapped bitter gourd peroxidase (BGP) has been employed for the treatment of disperse dyes: Disperse Brown 1 (DB 1) and Disperse Red 17 (DR 17). Peroxidase alone was unable to decolorize DR 17 and DB 1. However, the investigated dyes were decolorized maximally by BGP in the presence of 0.2 mmol/L redox mediator, violuric acid (VA). A slow decrease in percent decolorization was observed when VA concentration was higher than 0.2 mmol/L which could likely be due to the high reactivity of its aminoxyl radical (> N–O.) intermediate, that might undergo chemical reactions with aromatic amino acid side chains of the enzyme thereby inactivating it. Maximum decolorization of the dyes was observed at pH 3.0 and 40°C within 2 hr of incubation. Immobilized peroxidase decolorized 98% DR 17 and 71% DB 1 using 35 U of BGP in batch process in 90 min. Immobilized enzyme decolorized 85% DR 17 and 51% DB 1 whereas soluble enzyme decolorized DR 17 to 48% and DB 1 to 30% at 60°C. UV-visible spectral analysis was used to evaluate the degradation of these dyes and their toxicity was tested by Allium cepa test. The generally observed higher stability of the bioaffinity bound enzymes against various forms of inactivation may be related to the specific and strong binding of enzyme with bioaffinity support which prevents the unfolding/denaturation of enzyme. Thus entrapped peroxidase was found to be effective in the decolorization of the investigated dyes.     

Ameliorative effect of zinc oxide nanoparticles against potassium bromate-mediated toxicity in Swiss albino rats

Environmental Science and Pollution Research - Potassium bromate (PB) is a commonly used food additive, a prominent water disinfection by-product, and a class IIB carcinogen. It exerts a various...     

Modeling the dispersion of drilling muds using the bblt model: the effects of settling velocity

The benthic boundary layer transport (bblt) model was widely used in the Atlantic Canadian offshore region to assess the potential impact zones from drilling wastes discharges from offshore oil and gas drilling. The current version of the bblt uses a single-class settling velocity scenario, which may affect its performance, as settling velocity is size, shape, and material dependent. In this study, the effects of settling velocity on bblt predictions were assessed by replacing this single-class settling velocity scenario with a multi-class size-dependent settling velocity scenario. The new scenario was used in a hypothetical study to simulate the dispersion of barite and fine-grained drilling cuttings. The study showed that the effects of settling velocity on bblt predictions are spatial, temporal, and material dependent.