The biotransformation by Flavobacterium sp. of the following organophosphate pesticides was experimentally and theoretically studied: phorate, tetrachlorvinphos, methyl-parathion, terbufos, trichloronate, ethoprophos, phosphamidon, fenitrothion, dimethoate and DEF. The Flavobacterium sp. ATCC 27551 strain bearing the organophosphate-degradation gene was used. Bacteria were incubated in the presence of each pesticide for a duration of 7 days. Parent pesticides were identified and quantified by means of a gas-chromatography mass spectrum system. Activity was considered as the amount (micromol) of each pesticide degraded by Flavobacterium sp. Also, structural parameters obtained by means of the CAChe program package for biomolecules, the reactivity index of phosphorus, of oxygen at the P = O function and of sulfur at the P = S function, and lipophilicity (log Poct) (ALOGPS v. 2.0) were obtained for each pesticide. Pesticides were hydrolyzed at the bond between phosphorous and the heteroatom, producing phosphoric acid and three metabolites. Enzymatic activity was significantly explained by the following multiple linear relationship: Enzymatic activity = 162.2 - 9.5(dihedral angle energy) - 25.0(Total energy) - 0.51(Molecular weight). Finally, a mechanism of Flavobacterium sp. to hydrolyze pesticides was proposed.
Microbial enzymes that can hydrolyze organophosphorus compounds have been isolated, identified and characterized from different microbial species in order to use them in biodegradation of organophosphorus compounds. We isolated a bacterial strain Cons002 from an agricultural soil bacterial consortium, which can hydrolyze methyl-parathion (MP) and other organophosphate pesticides. HPLC analysis showed that strain Cons002 is capable of degrading pesticides MP, parathion and phorate. Pulsed-field gel electrophoresis and 16S rRNA amplification were performed for strain characterization and identification, respectively, showing that the strain Cons002 is related to the genus Enterobacter sp. which has a single chromosome of 4.6 Mb and has no plasmids. Genomic library was constructed from DNA of Enterobacter sp. Cons002. A gene called opdE (Organophosphate Degradation from Enterobacter) consists of 753 bp and encodes a protein of 25 kDa, which was isolated using activity methods. This gene opdE had no similarity to any genes reported to degrade organophosphates. When kanamycin-resistance cassette was placed in the gene opdE, hydrolase activity was suppressed and Enterobacter sp. Cons002 had no growth with MP as a nutrients source.
An important use of environmental indicators is oriented to know their individual impact on the whole environment quality. Nevertheless, most of the important causes of environment affectations are derived from multiple interactions between indicators which correspond more specifically to the environmental reality. The affectations derived from interactions should be analyzed and interpreted through numerical expressions representing a relevant challenge for developers of environmental indicators. To cope with the analysis and interpretation problem, we propose in this work a methodology in two senses: in a bottom-up sense a directed graph is built representing interactions between environmental indicators as behavioral relations, which exert an effect on the state of an environmental issue of a site over time (10 years); in a top-down sense to assist users in the analysis and interpretation of interactions through a computer interface that provides users with the capacity of knowing how and what relational behaviors between indicators are affecting, the most or the least, the performance of the environmental issue being studied. This methodology was applied to the analysis an interpretation of interactions between environmental variables that affect the state of an environmental quality issue related with the State of Morelos in Mexico. The results showed the adequate expressivity of a directed graph to represent interactions allowed to verify the coherence of the numerical values associated with their behaviors during a period of time and with their effects on the environmental issue under study.
The goal of this study was to optimize methyl parathion (O,O-dimethyl-O-4-p-nitrophenyl phosphorothioate) degradation using a strain of Escherichia coli DH5α expressing the opd gene. Our results indicate that this strain had lower enzymatic activity compared to the Flavobacterium sp. ATCC 27551 strain from which the opd gene was derived. Both strains were assessed for their ability to degrade methyl parathion (MP) in a mineral salt medium with or without the addition of glucose either as suspended cells or immobilized on tezontle, a volcanic rock. MP was degraded by both strains with similar efficiencies, but immobilized cells degraded MP more efficiently than cells in suspension. However, the viability of E. coli cells was much higher than that of the Flavobacterium sp. We confirmed the decrease in toxicity from the treated effluents through acetylcholinesterase activity tests, indicating the potential of this method for the treatment of solutions containing MP.
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