Gene cloning and molecular characterization of a two-enzyme system catalyzing the oxidative detoxification of beta-endosulfan

Molecular insight into endosulfan degradation by Ese protein from Arthrobacter: Evidence-based structural bioinformatics and quantum mechanical calculations

Endosulfan is an organochlorine insecticide widely used for agricultural pest control. Many nations worldwide have restricted or completely banned it due to its extreme toxicity to fish and aquatic invertebrates. Arthrobacter sp. strain KW has the ability to degrade α, β endosulfan and its intermediate metabolite endosulfate; this degradation is associated with Ese protein, a two-component flavin-dependent monooxygenase (TC-FDM). Employing in silico tools, we obtained the 3D model of Ese protein, and our results suggest that it belongs to the Luciferase Like Monooxygenase family (LLM). Docking studies showed that the residues V59, V315, D316, and T335 interact with α-endosulfan. The residues: V59, T60, V315, D316, and T335 are implicated in the interacting site with β-endosulfan, and the residues: H17, V315, D316, T335, N364, and Q363 participate in the interaction with endosulfate. Topological analysis of the electron density by means of the Quantum Theory of Atoms in Molecules (QTAIM) and the Non-Covalent Interaction (NCI) index reveals that the Ese-ligands complexes are formed mainly by dispersive forces, where Cl atoms have a predominant role. As Ese is a monooxygenase member, we predict the homodimer formation. However, enzymatic studies must be developed to investigate the Ese protein's enzymatic and catalytic activity.

Potential and limitations for monitoring of pesticide biodegradation at trace concentrations in water and soil

Pesticides application on agricultural fields results in pesticides being released into the environment, reaching soil, surface water and groundwater. Pesticides fate and transformation in the environment depend on environmental conditions as well as physical, chemical and biological degradation processes. Monitoring pesticides biodegradation in the environment is challenging, considering that traditional indicators, such as changes in pesticides concentration or identification of pesticide metabolites, are not suitable for many pesticides in anaerobic environments. Furthermore, those indicators cannot distinguish between biotic and abiotic pesticide degradation processes. For that reason, the use of molecular tools is important to monitor pesticide biodegradation-related genes or microorganisms in the environment. The development of targeted molecular (e.g., qPCR) tools, although laborious, allowed biodegradation monitoring by targeting the presence and expression of known catabolic genes of popular pesticides. Explorative molecular tools (i.e., metagenomics & metatranscriptomics), while requiring extensive data analysis, proved to have potential for screening the biodegradation potential and activity of more than one compound at the time. The application of molecular tools developed in laboratory and validated under controlled environments, face challenges when applied in the field due to the heterogeneity in pesticides distribution as well as natural environmental differences. However, for monitoring pesticides biodegradation in the field, the use of molecular tools combined with metadata is an important tool for understanding fate and transformation of the different pesticides present in the environment.

Potential Use of Microbial Community Genomes in Various Dimensions of Agriculture Productivity and Its Management: A Review

Agricultural productivity is highly influenced by its associated microbial community. With advancements in omics technology, metagenomics is known to play a vital role in microbial world studies by unlocking the uncultured microbial populations present in the environment. Metagenomics is a diagnostic tool to target unique signature loci of plant and animal pathogens as well as beneficial microorganisms from samples. Here, we reviewed various aspects of metagenomics from experimental methods to techniques used for sequencing, as well as diversified computational resources, including databases and software tools. Exhaustive focus and study are conducted on the application of metagenomics in agriculture, deciphering various areas, including pathogen and plant disease identification, disease resistance breeding, plant pest control, weed management, abiotic stress management, post-harvest management, discoveries in agriculture, source of novel molecules/compounds, biosurfactants and natural product, identification of biosynthetic molecules, use in genetically modified crops, and antibiotic-resistant genes. Metagenomics-wide association studies study in agriculture on crop productivity rates, intercropping analysis, and agronomic field is analyzed. This article is the first of its comprehensive study and prospects from an agriculture perspective, focusing on a wider range of applications of metagenomics and its association studies.

Study on the characterization of endosulfan-degrading bacterial strains isolated from contaminated rhizospheric soil

In the present study, we have isolated endosulfan tolerant bacterial strains from the rhizosphere of plants growing in a pesticide-contaminated area. The tolerance capacities of these strains were tested up to 50,000 µg ml^-1 of endosulfan. It was found that out of nineteen, four strains (EAG-EC-12, EAG-EC-13, EAG-EC-14, and EAG-EC-15) were capable of surviving up to 50,000 µg ml^-1 endosulfan concentration in the media; thus, these four strains were selected for the characterization. Among four, two strains were identified as Serratia liquefaciens, while the other two strains were Bacillus sp. and Brevibacterium halotolerans. The result shows that growth of strain Serratia liquefaciens 1 and Serratia liquefaciens 2 in treated medium was statistically similar to that of control (cfu 6.8 × 10⁷) after 24 h, while strains Bacillus sp. and Brevibacterium halotolerans have shown growth significantly less than the control. The degradation potential of these strains was analyzed against 100 to 250 µg ml^-1 of endosulfan in a Minimal Broth Medium (MBM), and it was recorded that only 9, 2, 7, and 19% of endosulfan (100 µg ml^-1) remain after a 72 h incubation period of Bacillus sp., Serratia liquefaciens 1, Serratia liquefaciens 2, and Brevibacterium halotolerans, respectively. This endosulfan removal potential of studied strains was decreased with an increase in concentration of endosulfan.

A Nafion/AChE-cSWCNT/MWCNT/Au-based amperometric biosensor for the determination of organophosphorous compounds

In the present study, a biosensor was developed for the detection of organophosphorous compounds. Core electrode of a working electrode was obtained by depositing the paste of Gold nanoparticles and Multi-walled Carbon Nanotubes on a gold wire. The acetylcholinesterase enzyme was immobilized on carboxylated Single-walled Carbon Nanotubes and pasted onto a core of electrode followed by coating with a nafion layer to prevent enzyme leaching from the electrode. This electrode was further used as a working electrode in the sensor. This sensor worked on the AChE inhibition mechanism where the signal is inversely proportional to the amount of organophosphorous compounds. The electrocatalytic activity of this sensor was observed at a potential of +0.360 mV. The standardized conditions for this sensor were pH at 7.0, temperature at 30°C and response time at less than 10s. The linear working range of this biosensor was 0.1-130 µM with the lowest detection limit (LOD) of 1.9, 2.3, 2.2 and 2.5 nM for Methyl Parathion, Monocrotophos, Chlorpyrifos and Endosulfan, respectively. The biosensor showed excellent reusability (upto 55 times) and can be stored stably for 2 months.

Degradation and conversion of endosulfan by newly isolated Pseudomonas mendocina ZAM1 strain

Endosulfan contamination is one of the major concerns of soil ecosystem, which causes detrimental effects not only to humans but also to animals and plants. Therefore, the aim of this study was to isolate and identify a novel bacterial strain capable of degrading endosulfan in agriculture contaminated soils. A novel bacterial strain was isolated from the sugarcane field contaminated with endosulfan, and was named as ZAM1 strain. The ZAM1 bacterial strain was further identified as Pseudomonas mendocina based on the biochemical and molecular analysis. 16sRNA sequence analysis of ZAM1 strain shows maximum similarity with known endosulfan-degrading bacteria (Pseudomonas putida), respectively. Enrichment was carried out using the endosulfan as sole sulfur source. The ZAM1 strain was able to use α and β endosulfan as a sole sulfur source. Our results showed that ZAM1 strain degrades endosulfan >64.5% (50 mg/l) after 12 days of incubation. The residues were analyzed by GC-MS analysis and confirmed the formation of metabolites of dieldrin, 2 heptanone, methyl propionate, and endosulfan lactone compounds. Hence, these results indicate that the ZAM1 strain is a promising bacterial source for detoxification of endosulfan residues in the environment.

Use of Ca-alginate immobilized Pseudomonas aeruginosa for repeated batch and continuous degradation of Endosulfan

The current investigation is taken up with the aim of studying repeated batch and continuous degradation of Endosulfan, using Ca-alginate immobilized cells of Pseudomonas aeruginosa isolated from an agricultural soil. The work involves the study of genes and enzymes involved in the degradation of the pesticide and was carried out with an objective of reducing the toxicity of Endosulfan by degrading it to less toxic metabolites. The long-term stability of Endosulfan degradation was studied during its repeated batch degradation, carried out over a period of 35 days. Immobilized cells of Ps. aeruginosa were able to show 60 % degradation of Endosulfan at the end of the 35th cycle with a cell leakage of 642 × 10⁴ Cfu/mL. During continuous treatment, with 2 % concentration of Endosulfan, 100 % degradation was recorded up to 100 mL/h flow rate and with 10 % concentration of the Endosulfan, and 100 and 85 % degradation was recorded at 20 mL/h flow rate and 100 mL/h flow rate, respectively. After degradation of Endosulfan, products were extracted from a large amount of spent medium using two volumes of ethyl acetate and subjected to the LC–MS analysis. Endosulfan lactone and Endosulfan ether were the products of degradation detected by the LCMS analysis. Plasmid curing experiments indicated that genes responsible for the degradation of Endosulfan are present on the chromosome and not on the plasmid, as growth of Ps. aeruginosa was observed on modified non-sulfur medium with Endosulfan after the plasmid was cured with ethidium bromide. The results of PCR indicated that there is no amplified product of ~1350 bp expected for esd gene, in Ps. aeruginosa, although there were some non-specific bands. Enzymatic degradation studies indicated that the enzymes involved in the degradation of Endosulfan are intracellular. With this investigation, it was indicated that immobilized cells of Ps.aeruginosa have the potential to be used in the bioremediation of water contaminated with Endosulfan.

Biodegradation of nicosulfuron by a novel Alcaligenes faecalis strain ZWS11

A bacterial strain ZWS11 was isolated from sulfonylurea herbicide-contaminated farmland soil and identified as a potential nicosulfuron-degrading bacterium. Based on morphological and physicochemical characterization of the bacterium and phylogenetic analysis of the 16S rRNA sequence, strain ZWS11 was identified as Alcaligenes faecalis. The effects of the initial concentration of nicosulfuron, inoculation volume, and medium pH on degradation of nicosulfuron were investigated. Strain ZWS11 could degrade 80.56% of the initial nicosulfuron supplemented at 500.0mg/L under the conditions of pH7.0, 180r/min and 30°C after incubation for 6days. Strain ZWS11 was also capable of degrading rimsulfuron, tribenuron-methyl and thifensulfuron-methyl. Four metabolites from biodegradation of nicosulfuron were identified, which were 2-aminosulfonyl-N, N-dimethylnicotinamide (M1), 4, 6-dihydroxypyrimidine (M2), 2-amino-4, 6-dimethoxypyrimidine (M3) and 2-(1-(4,6-dimethoxy-pyrimidin-2-yl)-ureido)-N,N-dimethyl-nicotinamide (M4). Among the metabolites detected, M2 was reported for the first time. Possible biodegradation pathways of nicosulfuron by strain ZWS11 were proposed. The degradation proceeded mainly via cleavage of the sulfonylurea bridge, O-dealkylation, and contraction of the sulfonylurea bridge by elimination of a sulfur dioxide group. The results provide valuable information for degradation of nicosulfuron in contaminated environments.

Cytochrome P450 BM3 of Bacillus megaterium - a possible endosulfan biotransforming gene

Computing chemistry was applied to understand biotransformation mechanism of an organochlorine pesticide, endosulfan. The stereo specific metabolic activity of human CYP-2B6 (cytochrome P450) on endosulfan has been well demonstrated. Sequence and structural similarity search revealed that the bacterium Bacillus megaterium encodes CYP-BM3, which is similar to CYP-2B6. The functional similarity was studied at organism level by batch-scale studies and it was proved that B. megaterium could metabolize endosulfan to endosulfan sulfate, as CYP-2B6 does in human system. The gene expression analyses also confirmed the possible role of CYP-BM3 in endosulfan metabolism. Thus, our results show that the protein structure based in-silico approach can help us to understand and identify microbes for remediation strategy development. To the best of our knowledge this is the first report which has extrapolated the bacterial gene for endosulfan biotransformation through in silico prediction approach for metabolic gene identification.

Biodegradation of endosulfan in broth medium and in soil microcosm by Klebsiella sp. M3

Nine endosulfan degrading bacterial strains were isolated by soil enrichment with endosulfan. Bacterial strain M3 was the most efficient degrader. Endosulfan degradation was accompanied by a decrease in pH of the medium and an increase in chloride ion concentration. The bacterium was tested for its ability to degrade endosulfan at different concentrations in broth and soil. Maximum degradation occurred at concentrations of 50 μg/ml of broth and 100 μg/g of soil. Values of Ks and Vmax were different for (α)- and (β)-endosulfan in broth. The kinetic indices (Vmax/Ks) for α-endosulfan and β-endosulfan were 0.051 and 0.048 day(-1) respectively, indicating that (α)-endosulfan was more rapidly degraded. Bacterial strain M3 was identified as Klebsiella sp. M3 on the basis of 16S rDNA sequence similarity (GenBank accession number JX273762).

Endosulfan induced alteration in bacterial protein profile and RNA yield of Klebsiella sp. M3, Achromobacter sp. M6, and Rhodococcus sp. M2

Three bacterial strains identified as Klebsiella sp. M3, Achromobacter sp. M6 and Rhodococcus sp. M2 were isolated by soil enrichment with endosulfan followed by shake flask enrichment technique. They were efficiently degrading endosulfan in the NSM (non sulfur medium) broth. Degradation of endosulfan was faster with the cell free extract of bacterial cells grown in the sulfur deficient medium (NSM) supplemented with endosulfan than that of nutrient rich medium (Luria Bertani). In the cell free extract of NSM supplemented with endosulfan as sole sulfur source, a unique band was visualized on SDS-PAGE but not with magnesium sulfate as the sole sulfur source in NSM and LB with endosulfan. Expression of a unique polypeptide band was speculated to be induced by endosulfan under sulfur starved condition. These unique polypeptide bands were identified as OmpK35 protein, sulfate binding protein and outer membrane porin protein, respectively, in Klebsiella sp. M3, Achromobacter sp. M6 and Rhodococcus sp. M2. Endosulfan showed dose dependent negative effect on total RNA yield of bacterial strains in nutrient rich medium. Absence of plasmid DNA indicated the presence of endosulfan metabolizing gene on genomic DNA.

Acetylcholinesterase biosensors for electrochemical detection of organophosphorus compounds: a review

The exponentially growing population, with limited resources, has exerted an intense pressure on the agriculture sector. In order to achieve high productivity the use of pesticide has increased up to many folds. These pesticides contain organophosphorus (OP) toxic compounds which interfere with the proper functioning of enzyme acetylcholinesterase (AChE) and finally affect the central nervous system (CNS). So, there is a need for routine, continuous, on spot detection of OP compounds which are the main limitations associated with conventional analytical methods. AChE based enzymatic biosensors have been reported by researchers as the most promising tool for analysis of pesticide level to control toxicity and for environment conservation. The present review summarises AChE based biosensors by discussing their characteristic features in terms of fabrication, detection limit, linearity range, time of incubation, and storage stability. Use of nanoparticles in recently reported fabrication strategies has improved the efficiency of biosensors to a great extent making them more reliable and robust.

Acetylcholinesterase inhibition-based biosensors for pesticide determination: a review

Pesticides released intentionally into the environment and through various processes contaminate the environment. Although pesticides are associated with many health hazards, there is a lack of monitoring of these contaminants. Traditional chromatographic methods-high-performance liquid chromatography, capillary electrophoresis, and mass spectrometry-are effective for the analysis of pesticides in the environment but have certain limitations such as complexity, time-consuming sample preparation, and the requirement of expensive apparatus and trained persons to operate. Over the past decades, acetylcholinesterase (AChE) inhibition-based biosensors have emerged as simple, rapid, and ultra-sensitive tools for pesticide analysis in environmental monitoring, food safety, and quality control. These biosensors have the potential to complement or replace the classical analytical methods by simplifying or eliminating sample preparation and making field-testing easier and faster with significant decrease in cost per analysis. This article reviews the recent developments in AChE inhibition-based biosensors, which include various immobilization methods, different strategies for biosensor construction, the advantages and roles of various matrices used, analytical performance, and application methods for constructing AChE biosensors. These AChE biosensors exhibited detection limits and linearity in the ranges of 1.0×10(-11) to 42.19 μM (detection limits) and 1.0×10(-11)-1.0×10(-2) to 74.5-9.9×10(3)μM (linearity). These biosensors were stable for a period of 2 to 120days. The future prospects for the development of better AChE biosensing systems are also discussed.

Isolation and characterization of a Pseudomonas sp. strain IITR01 capable of degrading α-endosulfan and endosulfan sulfate

AIM

To isolate bacteria capable of degrading endosulfan (ES) and the more toxic ES sulfate and to characterize their metabolites.

METHODS AND RESULTS

A Pseudomonas sp. strain IITR01 capable of degrading α-ES and toxic ES sulfate was isolated using technical-ES through enrichment culture techniques. No growth and no degradation were observed using β-ES. Thin-layer chromatography and gas chromatography-mass spectrum analysis revealed the disappearance of both α-ES and ES sulfate and the formation of hydroxylated products ES diol, ether and lactone. We show here for the first time the formation of aforementioned metabolites in contrast to ES hemisulfate yielded by an Arthrobacter sp. Metabolism of α-ES and endosulfate was also observed using the crude cell extract of IITR01. The molecular mass of protein induced during the degradation of α-ES and sulfate as substrate was found to be approximately 150 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

CONCLUSION

We describe characterization of bacterium capable of degrading α-ES and ES sulfate but not β-ES. Genetic investigation suggests that a gene nonhomologous to the reported esd may be present in the strain IITR01.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study describes toxic ES degradation by a Pseudomonas species that may be utilized for the bioremediation of the industrial soils contaminated with ES residues.

Endosulfan in China 1-gridded usage inventories

BACKGROUND, AIM, AND SCOPE

Endosulfan, an organochlorine pesticide (OCP), is genotoxic in mammalian cells and generally considered to be toxic and classified by the World Health Organization and the US Environmental Protection Agency as priority pollutants and a nominator for inclusion in a future iteration of the persistent organic pollutants treaty. Endosulfan is a currently used pesticide and still being used worldwide. The general trend of total global endosulfan use has increased continuously since the first year when this pesticide was applied. It is critical to create national endosulfan usage/emission inventories for China to carry out source-receptor relation analysis, risk assessment, and other research related to endosulfan in this country. Chinese inventories have been published for some OCPs, such as technical HCH and lindane, DDT, and chlordane; for endosulfan, however, there has not been any usage inventory available on any scales (national or provincial), although endosulfan has been widely used since 1994 in this country. This is the first part of the work. The goal of this paper is to quantify the historical production and usage of endosulfan in China and to compile gridded historical usage inventories of endosulfan for this country. Based on these usage inventories, emission and residue inventories will be created, which is the goal of the second part of the work.

MATERIALS AND METHODS

Due to the lack of national production and usage information of endosulfan in China, a method to estimate the use of endosulfan was developed. First, information of crops on which endosulfan is applied and average endosulfan use and annual application frequencies of endosulfan on these crops were collected. Secondly, usage of endosulfan on each crop was estimated using the national cropland area for each province from Chinese government reports. Finally, with the help of GIS (geographic information system), the usage data of this insecticide was allocated to a grid system, with a 1/4 degrees longitude by 1/6 degrees latitude resolution, with a size for each grid cell of approximately 25 km by 25 km.

RESULTS AND DISCUSSION

The use of endosulfan in agriculture in China started on cotton in 1994, and on wheat, tea, tobacco, apples, and other fruits in 1998. Endosulfan usage on cotton, wheat, tea, tobacco, and apples in China has been estimated to be approximately 25,700 t between 1994 and 2004. The province with the highest usage of endosulfan is Henan Province, with a total usage reaching 4,000 t, followed by the uses in Xinjiang Autonomous Region (3,200 t), Shandong Province (3,000 t), Hebei Province (2,100 t), and Anhui Province (1,900 t). Gridded usage inventories of endosulfan at a 1/4 degrees longitude by 1/6 degrees latitude resolution have been created, which indicate that the intensive endosulfan use was in the south of Hebei Province, west of Shandong Province, east of Henan Province, north of Anhui Province, east of Jiangsu Province, and some areas in Yunnan Province and Xinjiang Autonomous Region. General agreement has been found between the usage data from our estimation and the small amount of usage data published in China.

CONCLUSIONS

This is the first national gridded endosulfan usage inventory produced for China. The annual applications of endosulfan from 1994 to 2004 in China were estimated based on the total areas of major crops, on which endosulfan was applied, and spatial distribution of the application was generated at provincial and prefecture levels. With the help of GIS, endosulfan usage based on prefecture was transferred to a 1/4 degrees longitude by 1/6 degrees latitude gridding system. The satisfaction of the inventories was supported by the consistence between the estimation of the annual usage and the reported annual production of endosulfan.

RECOMMENDATIONS AND PERSPECTIVES

This gridded endosulfan usage inventory created in this study will be improved upon availability of new information of endosulfan. The usage inventories can be used to create gridded emission and residue inventories for this insecticide. It is believed that this work will pave the way for further endosulfan studies in China and beyond.

Bacterial degradation of aromatic compounds

Aromatic compounds are among the most prevalent and persistent pollutants in the environment. Petroleum-contaminated soil and sediment commonly contain a mixture of polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatics. Aromatics derived from industrial activities often have functional groups such as alkyls, halogens and nitro groups. Biodegradation is a major mechanism of removal of organic pollutants from a contaminated site. This review focuses on bacterial degradation pathways of selected aromatic compounds. Catabolic pathways of naphthalene, fluorene, phenanthrene, fluoranthene, pyrene, and benzo[a]pyrene are described in detail. Bacterial catabolism of the heterocycles dibenzofuran, carbazole, dibenzothiophene, and dibenzodioxin is discussed. Bacterial catabolism of alkylated PAHs is summarized, followed by a brief discussion of proteomics and metabolomics as powerful tools for elucidation of biodegradation mechanisms.

The enzymatic basis for pesticide bioremediation

Enzymes are central to the biology of many pesticides, influencing their modes of action, environmental fates and mechanisms of target species resistance. Since the introduction of synthetic xenobiotic pesticides, enzymes responsible for pesticide turnover have evolved rapidly, in both the target organisms and incidentally exposed biota. Such enzymes are a source of significant biotechnological potential and form the basis of several bioremediation strategies intended to reduce the environmental impacts of pesticide residues. This review describes examples of enzymes possessing the major activities employed in the bioremediation of pesticide residues, and some of the strategies by which they are employed. In addition, several examples of specific achievements in enzyme engineering are considered, highlighting the growing trend in tailoring enzymatic activity to a specific biotechnologically relevant function.

Microbial biodiversity and in situ bioremediation of endosulfan contaminated soil

Molecular characterization based on 16s rDNA gene sequence analysis of bacterial colonies isolated from endosulfan contaminated soil showed the presence of Ochrobacterum sp, Burkholderia sp, Pseudomonas alcaligenes, Pseudomonas sp and Arthrobacter sp which degraded 57-90% of α-endosulfan and 74-94% of β-endosulfan after 7days. Whole cells of Pseudomonas sp and Pseudomonas alcaligenes showed 94 and 89% uptake of α-isomer and 86 and 89% of β-endosulfan respectively in 120 min. In Pseudomonas sp, endosulfan sulfate was the major metabolite detected during the degradation of α-isomer, with minor amount of endosulfan diol while in Pseudomonas alcaligenes endosulfan diol was the only product during α-endosulfan degradation. Whole cells of Pseudomonas sp also utilized 83% of endosulfan sulfate in 120 min. In situ applications of the defined consortium consisting of Pseudomonas alcaligenes and Pseudomonas sp (1:1) in plots contaminated with endosulfan showed that 80% of α-endosulfan and 65% of β-endosulfan was degraded after 12 weeks of incubation. Endosulfan sulfate formed during endosulfan degradation was subsequently degraded to unknown metabolites. ERIC-PCR analysis indicated 80% survival of introduced population of Pseudomonas alcaligenes and Pseudomonas sp in treated plots.

Persistence and distribution of endosulfan under field condition

Rapid increase in industrialization and agricultural activities to meet the population need has led to environmental pollution. The major revolution in agricultural production is mainly due to increased use of pesticides and fertilizers. Soil act as a major sink for majority of pesticides applied on agricultural crops. Among the organochlorines, endosulfan is the most commonly used pesticide, hence this study concentrates on the persistence and distribution behaviour of endosulfan under field conditions. The result showed that the alpha endosulfan concentrations were very minimum (0.98 mg/kg of soil) in all the four fields under study (Nazarath, Othikadu, Ekkadu and Ekkadukandigai of Thiruvallur district, Tamil Nadu). Where as beta endosulfan concentration at the time of application was 6.39 mg/kg and declined to 0.8 mg/kg on soil at 150th day. The endosulfan sulfate concentration was 11.8 mg/kg in soil at 15th day and then concentration declined to 2.2 mg/kg at 150th day. Field run-off samples showed maximum residue levels (0.024 mg/l) at the early irrigation period. While plant foliar parts showed maximum concentrations of alpha-endosulfan (43.4 mg/kg), beta-endosulfan (40.6 mg/kg) and endosulfan sulfate (20.1 mg/kg). At harvest stage, rice grain and husk also had lower concentrations of endosulfan sulfate (2.2 and 0.09 mg/kg), respectively.

A single monooxygenase, ese, is involved in the metabolism of the organochlorides endosulfan and endosulfate in an Arthrobacter sp

In this paper we describe isolation of a bacterium capable of degrading both isomers of the organochloride insecticide endosulfan and its toxic metabolite, endosulfate. The bacterium was isolated from a soil microbial population that was enriched with continuous pressure to use endosulfate as the sole source of sulfur. Analysis of the 16S rRNA sequence of the bacterium indicated that it was an Arthrobacter species. The organochloride-degrading activity was not observed in the presence of sodium sulfite as an alternative sulfur source, suggesting that the activity was part of the sulfur starvation response of the strain. A gene, ese, encoding an enzyme capable of degrading both isomers of endosulfan and endosulfate was isolated from this bacterium. The enzyme belongs to the two-component flavin-dependent monooxygenase family whose members require reduced flavin for activity. Nuclear magnetic resonance analyses identified the metabolite of endosulfan as endosulfan monoalcohol and the metabolite of endosulfate as endosulfan hemisulfate. The ese gene was located in a cluster of 10 open reading frames encoding proteins with low levels of sulfur-containing amino acids. These open reading frames were organized into two apparent divergently orientated operons and a gene encoding a putative LysR-type transcriptional regulator. The operon not containing ese did contain a homologue whose product exhibited 62% amino acid identity to the ese-encoded protein.

Endosulfan degradation by a Rhodococcus strain isolated from earthworm gut

A Rhodococcus MTCC 6716 bacterial strain was isolated apparently for the first time from the gut microflora of an Indian earthworm (Metaphire posthuma). Endosulfan was used as a carbon source by the strain and degraded it up to 92.58% within 15 days. Furthermore, the isolated strain of the bacterium did not produce the persistent form of the toxic metabolite endosulfan sulfate. This strain exhibits luxury growth in minimal medium with high concentrations of endosulfan (80 microg mL(-1)). Degradation of the endosulfan occurred simultaneously with bacterial growth and an increase in chloride ion (87.1%) in the growth medium, suggesting nearly complete degradation of the insecticide. This strain is able to tolerate 45 degrees C and retain its degradation potential even under sunlight exposure. Since endosulfan is used worldwide for pest control and its residues have been retained for long periods in soil, water, and agricultural products, the strain isolated by us is valuable for bioremediation of endosulfan-contaminated soil and water.

Biodegradation of the organochlorine insecticide, endosulfan, and the toxic metabolite, endosulfan sulfate, by Klebsiella oxytoca KE-8

Biodegradation of endosulfan, a chlorinated cyclodiene insecticide, is generally accompanied by production of the more toxic and more persistent metabolite, endosulfan sulfate. Since our reported endosulfan degrader, Klebsiella pneumoniae KE-1, failed to degrade endosulfan sulfate, we tried to isolate an endosulfan sulfate degrader from endosulfan-polluted soils. Through repetitive enrichment and successive subculture using mineral salt medium containing endosulfan or endosulfan sulfate as the sole source of carbon and energy, we isolated a bacterium capable of degrading endosulfan sulfate as well as endosulfan. The bacterium KE-8 was identified as Klebsiella oxytoca from the results of 16S rDNA sequence analysis. In biodegradation assays with KE-8 using mineral salt medium containing endosulfan (150 mg l(-1)) or endosulfan sulfate (173 mg l(-1)), the biomass was rapidly increased to an optical density at 550 nm of 1.9 in 4 days and the degradation constants for alpha- and beta-endosulfan, and endosulfan sulfate were 0.3084, 0.2983 and 0.2465 day(-1), respectively. Analysis of the metabolites further suggested that K. oxytoca KE-8 has high potential as a biocatalyst for bioremediation of endosulfan and/or endosulfan sulfate.

The phosphotriesterase gene opdA in Agrobacterium radiobacter P230 is transposable

We report a transposase gene (tnpA) upstream of the opdA phosphotriesterase gene of Agrobacterium radiobacter P230, as well as inverted repeats indicative of insertion sequences, flanking the two genes. Both the tnpA gene and the inverted repeats resemble the Tn610 transposon from Mycobacterium fortuitum. Two additional putative open reading frames separate opdA and tnpA with inferred translation products with similarity to two proteins encoded on the Geobacillus stearothermophilus IS5376 transposon. To test the proposition that these genes were contained on a transposon, an artificial composite transposon was constructed. This artificial transposon was then delivered into Escherichia coli DH10beta cells. Transposition was demonstrated by the presence of opdA on the E. coli chromosome and confirmation of insertion by inverse polymerase chain reaction. The data presented suggest a possible role of transposition in the distribution of the opd/opdA genes across a wide range of soil bacteria.