Degradation Of Such Compounds Research Articles

UNDERSTANDING THE ROLE OF BACTERIAL GENES AND ENZYMES IN ORGANOPHOSPHATE DEGRADATION: A STEP TOWARDS ENHANCED BIOREMEDIATION

The use of Organophosphates (OPs) as pesticides and insecticides increased after world war II, although organophosphates (OPs) are comparatively less persistent in the environment, but are highly toxic to animals. OP toxicity is causing a threat to biodiversity, hence it becomes essential to deal with the degradation of such compounds. Various techniques like photolysis, and chemical degradation have been used for OP degradation but these techniques are not costeffective and require ex-situ treatment, hence bioremediation is considered a potential alternative for OP degradation. Understanding the degradation pathways followed by different bacteria, genes and enzymes involved in such pathways can act as a step towards the development of an effective bioremediation technique for OP degradation. Recombinant biotechnology and protein engineering are used to develop designer bacteria, biocatalysts and enzymes with enhanced activity for OP-degrading bacteria. The present review highlights the bacterial degradation pathways, genes and enzymes involved in bioremediation pathways and new approaches for the development of OP bioremediation techniques.

Effectiveness of a simple biomixture for the adsorption and elimination of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide and its metabolite, 2,4-dichlorophenol (2,4-DCP), for a biobed system

The remediation of point-source contamination of herbicides in productive fields can be addressed with biopurification systems which require biomixtures of natural materials with effectiveness for the adsorption and degradation of such compounds. A biomixture of wheat stubble and soil was tested for the adsorption and degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and one of its main metabolites, 2,4-dichlorophenol (2,4-DCP). Single-contaminant kinetic studies were performed, being the pseudo-second order kinetic model the most suitable to describe the adsorption of both compounds. Although the adsorption of 2,4-D was faster, the adsorption of 2,4-DCP was three times higher. Single and competitive adsorption isotherms were also obtained. The later were acquired from a complete factorial experimental design varying the concentration of both solutes. Mathematical models were applied to describe the single solute isotherms, given a maximum monolayer adsorption capacity of 155.7 mg kg−1 for 2,4-D and 371.6 mg kg−1 for 2,4-DCP. Multicomponent models for bi-solute isotherms showed a clear reduction of 2,4-D adsorption in the presence of 2,4-DCP, although no adsorption displacement for the 2,4 DCP metabolite was observed. A stagnant degradation study was run and the contaminants were surveyed during 30 days. The biomixture was successful in degrading the 2,4-D, with a removal effectiveness > 96% after 15 days. The 2,4-DCP was not detected, suggesting a very fast degradation as soon as generated.

Biodegradation Aspects of Carbendazim and Sulfosulfuron: Trends, Scope and Relevance

A large amount of pesticides are being used now-a-days in crop protection which has resulted in buildup of such harmful compounds in the environment, proving a menace to humans, animal life as well as to soil microbes. Residues of these pesticides have been reported in soil, water and foods. Carbendazim and sulfosulfuron are among the most widely used pesticides for treating fungal diseases and unwanted herbs in crops respectively. Carbendazim is a benzimidazole fungicide which can harm liver as well as the endocrine system and suspected to have mutagenic and tumorigenic effects. On similar lines sulfosulfuron, a sulfonylurea herbicide may result in the development of resistant herbs displaying its carry-over effects to the next crop cultivated. These pesticides possess large half-lives and thus remain persistent in the environment which may lead to harmful consequences in near future. Besides chemical and photo-catalytic degradation of pesticides, microbial degradation has now been evolved as a much effective and safer way to eradicate these harmful compounds from the environment. However a limited literature is available on the microbial degradation of such compounds. The present review emphasizes mainly upon the chemical properties of Carbendazim and Sulfosulfuron, detection of their residues, harmful effects and insights into their degradation studies. Further, the use of efficient microbes for remediation of pesticides from the environment has been discussed.

Treatment of acetamiprid insecticide from artificially contaminated water by colloidal manganese dioxide in the absence and presence of surfactants

Acetamiprid is one of the most important pesticides and is effective against a number of insects. The increasing use of insecticides in the agricultural field is associated with a significant risk to water resources and aquatic systems. Thus the degradation of such compounds, after fulfillment of their insecticidal role, is essential to eliminate or minimize the contamination of water. The degradative treatment of acetamiprid insecticide from artificially contaminated water by water soluble colloidal MnO2 in acidic medium (HClO4) has been studied spectrophotometrically in the absence and presence of surfactants. The experiments have been performed under the pseudo-first-order reaction conditions with respect to MnO2. The degradation kinetics has been observed to be first-order with respect to MnO2 while fractional-order in both acetamiprid and HClO4. The anionic surfactant, sodium dodecyl sulfate (SDS) has been observed to be ineffective. On the other hand the reaction in the presence of cationic surfactant, cetyltrimethyl ammonium bromide (CTAB) could not be followed as well because it possesses a positive charge opposite to that of colloidal MnO2 causing flocculation and therefore could not be studied further. However, the addition of non-ionic surfactant, polyethylene glycol tert-octylphenyl ether (TX-100) accelerates the reaction rate. The catalytic effect of TX-100 has been discussed in the light of the available mathematical model. The kinetic data have been exploited to generate the various activation parameters for the oxidative degradation of acetamiprid by colloidal MnO2 in the absence and presence of non-ionic surfactant, TX-100.

A Self-Regulated Fed-Batch Reactor Part I – The Principle

A new fed-batch reactor was developed to conduct aerobic biodegradation studies. Its unique feature lies in the ability to self-regulate feed addition, according to the evolution of the degradation process, which is proportional to gaseous products formed, mainly CO2. The reactor is particularly well suited to evaluate intrinsic biokinetic parameters, since it allows to be reached equilibrium states (substrate-biomass. Application to kinetic studies of inhibitory or toxic compounds seems to be quite promising, given that feed is made dependent on the capacity and pace of the biomass to handle the degradation of such compounds.

Prolonging cell-free protein synthesis by selective reagent additions.

Factors causing the early cessation of protein synthesis have been studied in a cell-free system from Escherichia coli. We discovered that phosphoenol pyruvate (PEP), the secondary energy source for ATP regeneration, and several amino acids are rapidly degraded during the cell-free protein synthesis reaction. The degradation of such compounds takes place even in the absence of protein synthesis. This degradation severely reduces the capacity for protein synthesis. The lost potency was completely recovered when the reaction mixture was supplied with additional PEP and amino acids. Of the 20 amino acids, only arginine, cysteine, and tryptophan were required to restore system activity. Through repeated additions of PEP, arginine, cysteine,and tryptophan, the duration of protein synthesis was greatly extended. In this fed-batch reaction, after a 2 h incubation, the level of cell-free synthesized chloramphenicol acetyl transferase (CAT) reached 350 microg/mL, which is 3.5 times the yield of the batch reaction. Addition of fresh magnesium further extended the protein synthesis. As a result, through coordinated additions of PEP, arginine, cysteine, tryptophan, and magnesium, the final concentration of cell-free synthesized CAT increased more than 4-fold compared to a batch reaction. SDS-PAGE analysis of such a fed-batch reaction produced an obvious band of CAT upon Coomassie Blue staining.

Bimolecular OH Rate Constants of Organic Compounds in Solution 2. Measurements in 1,2,2-Trichlorotrifluoroethane Using Hydrogen Peroxide as an OH Source

Semivolatile organic compounds (SOC) occur in the troposphere either adsorbed at aerosol particles or in the free gas phase, depending on temperature, vapor pressure of the compound, and total particular surface. In order to estimate the abiotic degradation of such compounds, the OH reaction rate constant must be known, which cannot be measured directly in the gas phase at the relevant temperature due to experimental difficulties. In the method proposed here, the inert solvent 1,1,2-trichlorotrifluoroethane is used as the reaction medium and hydrogen peroxide as photolytic OH source. Relative reaction rates can be measured, using a reference compound of known k OH air. The relative rates can be converted into absolute ones due to the 1:1 relationship observed by Dilling, Gonsior, Boggs, and Mendoza (1988) Environ. Sci. Technol. 22, 1447-1453, between the relative rates in the inert solvent and those in the gas phase.

In situ mineralization of chlorinated phenols by pelagic bacteria in lakes of differing humic content

The microbial mineralization of phenol and three chlorinated phenols (3,4-dichlorophenol, 2,4,5-trichlorophenol and pentachlorophenol) in the water column of 23 pristine, oligotrophic lakes of different humic content was investigated. During short-term (∼2 d) in situ incubations of water samples amended with 14C-labeled phenolic compounds, the fraction of the added pollutant mineralized to 14CO2 was positively correlated with water color (an estimate of humic content) and the total organic carbon concentration of the water. The rate of mineralization per bacterial cell was not correlated with humic content, due to increased bacterial abundance with increasing humic content. Hence, the higher mineralization rate in humic lakes than in clear-water lakes was probably a result of higher bacterial abundance rather than being an effect of bacterial cells having a higher potential for the degradation of such compounds.

IN SITU MINERALIZATION OF CHLORINATED PHENOLS BY PELAGIC BACTERIA IN LAKES OF DIFFERING HUMIC CONTENT

The microbial mineralization of phenol and three chlorinated phenols (3,4-dichlorophenol, 2,4,5-trichlorophenol and pentachlorophenol) in the water column of 23 pristine, oligotrophic lakes of different humic content was investigated. During short-term (∼2 d) in situ incubations of water samples amended with 14C-labeled phenolic compounds, the fraction of the added pollutant mineralized to 14CO2 was positively correlated with water color (an estimate of humic content) and the total organic carbon concentration of the water. The rate of mineralization per bacterial cell was not correlated with humic content, due to increased bacterial abundance with increasing humic content. Hence, the higher mineralization rate in humic lakes than in clear-water lakes was probably a result of higher bacterial abundance rather than being an effect of bacterial cells having a higher potential for the degradation of such compounds.

Uptake, metabolism and mutagenic activity of aromatic glycidyl compounds

Aromatic diglycidyl compounds are very active mutagens when assayed in in vitro tests. In vivo, however, resorcinol diglycidyl ether provided no evidence for the clastogenic activity, while diglycidylaniline exhibited definite mutagenic activity in the micronucleus test. Since the only difference between these two compounds lies in the binding mode of the glycidyl groups to the aromatic nucleus (i.e. ether oxygen vs. aminic nitrogen), this apparent discrepancy in mutagenic activity led to the question of the mechanisms involved in such an activity difference. Although no clear signs of differential uptake or excretion could be detected in mice, differences could be seen in the spectrum of urinary metabolites; while resorcinol diglycidyl ether seemed to become fully converted to the genetically inactive bis-diol compound, a sizeable proportion of diglycidylaniline was converted only to the diol-epoxide. In vitro investigations and enzyme kinetic measurements with postmitochondrial supernatant of rat or mouse liver homogenate (S-9) finally yielded the biochemical explanation for this behaviour, as they showd a very low affinity of the diol-epoxide metabolite of diglycidylaniline for the epoxide hydrolase, normally involved in the degradation of such compounds. The diol-epoxide obtained from resorcinol diglycidyl ether, on the other hand, has an affinity to the degradation enzyme similar to, or even higher than, the one measured with the parent substance.

Interaction between herbicides and soil microorganisms.

Herbicides have been selected for their ability to act in a phytotoxic manner. Whilst considerable research effort has been conducted into their spectrum of activity on plants and animals (including man), little attention has been paid to the interaction between these compounds and the soil microorganisms. Yet it is largely through the activity of this flora that the fertility of the soil is maintained (Burgess and Raw 1967). The realization that some interaction could exist did not become apparent until studies on the persistence of these herbicides in the soil showed that whilst some compounds survived for a considerable length of time, others were degraded (Audus 1964, Kearney and Kaufman 1969). Parallel studies on insecticides showed that many of these could also persist for long times in the soil (Way and Scopes 1968). In this work, heavy treatments of phorate 1 and menazon were found to kill a large fraction of the soil population before degradation took place. The rate of degradation was found to vary enormously from pesticide to pesticide. Some of the organochlorine pesticides have been found to take years to disappear from the soil. There is some evidence that microorganisms may play a role by a very slow degradation of such compounds. Dieldrin, for example, can be partially hydrolysed by the bacterium, Aerobacter aerogenes (Wedemeyer 1968).