Molecular aspects of pesticide degradation by microorganisms

A SWMM-Based Screening Model for Estimating Wastewater Treatment Burden of Pesticides on the Urban Scale

To estimate the treatment load of pesticides for wastewater treatment plants (WWTPs) on an urban scale, we developed a SWMM-based screening model that integrates the mass balance of pesticides in residential soil and the storm-water runoff passing through residential lawns. Furthermore, we introduce an approximate approach that simplifies the simulation using the octanol-water partition coefficients (i.e., log K_OW) of pesticides. The results indicate that the simulated transport factors (i.e., the dissipation kinetics-relevant property from the soil) of systemic pesticides (i.e., log K_OW < 2.0) are constant, whereas those of non-systemic pesticides decrease with increasing log K_OW, indicating that highly lipophilic pesticides are thermodynamically favored for soil absorption. By using the approximate approach, we estimated the total mass of pesticides entering the urban sewer system and the pesticide concentrations in the influent of WWTPs for a midsize city. The results indicate that the estimated concentration of systemic pesticides in the influent is ~9.2 ng L^-1 and that of pesticides with log K_OW values above 3.0 is below 0.84 ng L^-1. The pesticide concentrations are consistent with published field data, indicating that the approximate approach can be applied as preliminary modeling tool to recommend pretreatment values for urban WWTPs. Although the model must be further validated and refined using field data, the screening method can be used to help urban planners and engineers to manage the treatment process of pesticides in WWTPs.

Current status of pesticide effects on environment, human health and it's eco-friendly management as bioremediation: A comprehensive review

Pesticides are either natural or chemically synthesized compounds that are used to control a variety of pests. These chemical compounds are used in a variety of sectors like food, forestry, agriculture and aquaculture. Pesticides shows their toxicity into the living systems. The World Health Organization (WHO) categorizes them based on their detrimental effects, emphasizing the relevance of public health. The usage can be minimized to a least level by using them sparingly with a complete grasp of their categorization, which is beneficial to both human health and the environment. In this review, we have discussed pesticides with respect to their global scenarios, such as worldwide distribution and environmental impacts. Major literature focused on potential uses of pesticides, classification according to their properties and toxicity and their adverse effect on natural system (soil and aquatic), water, plants (growth, metabolism, genotypic and phenotypic changes and impact on plants defense system), human health (genetic alteration, cancer, allergies, and asthma), and preserve food products. We have also described eco-friendly management strategies for pesticides as a green solution, including bacterial degradation, myco-remediation, phytoremediation, and microalgae-based bioremediation. The microbes, using catabolic enzymes for degradation of pesticides and clean-up from the environment. This review shows the importance of finding potent microbes, novel genes, and biotechnological applications for pesticide waste management to create a sustainable environment.

Biotechnological tools to elucidate the mechanism of pesticide degradation in the environment

Pesticides are widely used in agriculture, households, and industries; however, they have caused severe negative effects on the environment and human health. To clean up pesticide contaminated sites, various technological strategies, i.e. physicochemical and biological, are currently being used throughout the world. Biological approaches have proven to be a viable method for decontaminating pesticide-contaminated soils and water environments. The biological process eliminates contaminants by utilizing microorganisms' catabolic ability. Pesticide degradation rates are influenced by a variety of factors, including the pesticide's structure, concentration, solubility in water, soil type, land use pattern, and microbial activity in the soil. There is currently a knowledge gap in this field of study because researchers are unable to gather collective information on the factors affecting microbial growth, metabolic pathways, optimal conditions for degradation, and genomic, transcriptomic, and proteomic changes caused by pesticide stress on the microbial communities. The use of advanced tools and omics technology in research can bridge the existing gap in our knowledge regarding the bioremediation of pesticides. This review provides new insights on the research gaps and offers potential solutions for pesticide removal from the environment through the use of various microbe-mediated technologies.

UV and temperature effects on chloroacetanilide and triazine herbicides degradation and cytotoxicity

The purpose of this study was to explore the stability and toxicity of the herbicides and their degradation byproduct after exposure to different environmental factors. Triazines (atrazine, propazine, simazine) and chloroacetanilides (acetochlor, alachlor, metolachlor) which are commonly used herbicides were evaluated for cytotoxicity in different UV (254 nm and 365 nm) and temperature (4 °C, 23 °C, and 40 °C) conditions as well as degradation rates. Atrazine with the highest LD50 (4.23 μg mL-1) was less toxic than the other tested triazine herbicides Chloroacetanilides tested were more toxic than tested triazines, with LD50 0.08-1.42 μg mL-1 vs 1.44-4.23 μg mL-1, respectively. Alachlor with LD50 0.08 μg mL-1 showed the strongest toxic response as compared with other tested herbicides. Temperatures only did not alter cytotoxicity of the tested herbicides, except for acetochlor and alachlor showing about 45 % more cell death after exposure to 40 °C for 2 h. At all 3 tested temperatures, 2 h of UV treatments did not affect cytotoxic effects of the tested herbicides, except for acetochlor and alachlor. At 4 °C, acetochlor toxicity was attenuated about 63 % after UV 365 nm exposure; but alachlor toxicity was enhanced after either UV 254 or 365 nm exposure for about 40 % and 24 %, respectively. At 23 °C, acetochlor toxicity was enhanced about 35 % after UV 254 nm exposure, but attenuated about 48 % after UV 365 nm exposure. Alachlor toxicity was enhanced about 34 % after UV 254 nm and 23 °C exposure. In combination of UV 254 nm and 40 °C, acetochlor toxicity was lowered by 63 % and alachlor toxicity was no change as compared with 4 °C, no UV group. After co-treatment with UV 365 nm and 40 °C both acetochlor and alachlor toxicity was enhanced 55 % and 80 %, respectively. Through degradation analysis by LC-MS/MS, alachlor showed the most dramatic degradation (only 0.58 %-10.58 % remaining) after heat and UV treatments.

Plasmid-Mediated Biodegradation of Chlorpyrifos and Analysis of Its Metabolic By-Products

Organophosphate pesticide persistence is an emerging menace to the environment and despite this fact, its use has been enhanced due to its high efficiency. Bioremediation using microorganisms would be the only means by which these hazardous compounds could be wiped out without disturbing the environmental harmony. The current work studied the molecular mechanism of degradation of Chlorpyrifos (CP) by a bacterial consortium C5 comprising of three soil isolates Staphylococcus warneri (CPI 2), Pseudomonas putida (CPI 9) and Stenotrophomonas maltophilia (CPI 15), which unveiled that the property is plasmid borne. All the isolates were found to possess a 4 kb plasmid which could be cured only by using sodium azide. The Escherichia coli JM109 cells when transformed individually with the plasmid of the isolates showed CP degradation in mineral salts medium (MSM) that contained CP as the sole carbon source. The degradative enzyme organophosphorus hydrolase (~ 60 KDa) of the isolates was extracted and purified to 31.85, 26 and 37.74 fold, respectively. The possible metabolic by-products of CP degradation by the consortium C5, were also analysed. The LC-Q-Tof MS analysis revealed the presence of the major metabolite 3, 5, 6 -trichloropyridine (TCP) with the formation of chlorpyrifos oxon as the intermediate. The isolates also showed trichloropyridine degradation (> 80%) individually in MSM-TCP medium proving its efficiency to remediate both CP and TCP.

A comprehensive review on enzymatic degradation of the organophosphate pesticide malathion in the environment

A comprehensive review of available bioremediation technologies for the pesticide malathion is presented. This review article describes the usage and consequences of malathion in the environment, along with a critical discussion on modes of metabolism of malathion as a sole source of carbon, phosphorus, and sulfur for bacteria, and fungi along with the biochemical and molecular aspects involved in its biodegradation. Additionally, the recent approaches of genetic engineering are discussed for the manipulation of important enzymes and microorganisms for enhanced malathion degradation along with the challenges that lie ahead.

Genomic Analysis of γ-Hexachlorocyclohexane-Degrading Sphingopyxis lindanitolerans WS5A3p Strain in the Context of the Pangenome of Sphingopyxis

Sphingopyxis inhabit diverse environmental niches, including marine, freshwater, oceans, soil and anthropogenic sites. The genus includes 20 phylogenetically distinct, valid species, but only a few with a sequenced genome. In this work, we analyzed the nearly complete genome of the newly described species, Sphingopyxislindanitolerans, and compared it to the other available Sphingopyxis genomes. The genome included 4.3 Mbp in total and consists of a circular chromosome, and two putative plasmids. Among the identified set of lin genes responsible for γ-hexachlorocyclohexane pesticide degradation, we discovered a gene coding for a new isoform of the LinA protein. The significant potential of this species in the remediation of contaminated soil is also correlated with the fact that its genome encodes a higher number of enzymes potentially involved in aromatic compound degradation than for most other Sphingopyxis strains. Additional analysis of 44 Sphingopyxis representatives provides insights into the pangenome of Sphingopyxis and revealed a core of 734 protein clusters and between four and 1667 unique proteins per genome.

Chlorothalonil tolerance of indole producing bacteria associated to wheat (Triticum turgidum L.) rhizosphere in the Yaqui Valley, Mexico

Chlorothalonil is a commonly used fungicide to control the karnal bunt caused by Tilletia indica Mitra in wheat production from the Yaqui Valley, Mexico. Here, the effect of Chlorothalonil on the growth of 132 bacterial strains associated with wheat rhizosphere from the Yaqui Valley was evaluated, as well as their ability to produce indoles. Thirty-three percent of the evaluated strains were inhibited by Chlorothalonil, being Bacillus and Paenibacillus the most inhibited genera, observing an inhibition >50% of their strains. In addition, 49% of the inhibited strains showed the ability to produce indoles (>5 μg/mL), where the genus Bacillus was the most abundant (80%). The remaining strains (67%) were tolerant to the evaluated fungicide, but only 37% of those showed the ability to produce indoles, which could be considered as Plant Growth Promoting Rhizobacteria (PGPR). These results showed that Chlorothalonil is not only an antifungal compound but also inhibits the growth of bacterial strains with the ability to produce indoles. Thus, the intensive application of fungicides to agro-systems needs more validation in order to develop sustainable agricultural practices for food production.

Molecular characterization of monocrotophos and chlorpyrifos tolerant bacterial strain for enhancing seed germination of vegetable crops

The main aim of this study is to investigate the toxicity of organophosphate (OPs) insecticides monocrotophos (MCP) and chlorpyrifos (CLS) on plant growth promoting (PGP) properties and seed germination of brinjal, tomato and okra vegetables inoculated by Microbacterium hydrocarbonoxydans (BHUJP-P1), Stenotrophomonas rhizophila (BHUJP-P2), Bacillus licheniformis (BHUJP-P3) and Bacillus cereus (BHUJP-P4). Maximum increase in microbial growth (52.6% & 47.9%) with enhanced EPS production (447.67 mg/ml & 75.00 mg/ml) was showed by BHUJP-P4 and BHUJP-P3 at 10× dose of MCP and CLS over control, BHUJP-2 and BHUJP-P1 respectively. Simultaneously, both strains recorded minimum reduction in PGP activities and seed germination at 3× dose of both insecticides as compared to BHUJP-2 and BHUJP-P1, respectively. Strains BHUJP-P3 and BHUJP-P4 showed 83 and 81% of monocrotophos degradation at 50 mg/kg concentration; 81 and 80% at 150 mg/kg concentration within 5days respectively. Concurrently, these strains BHUJP-P3 and BHUJP-P4 were recorded 53 and 90% of chlorpyrifos degradation at 50 mg/kg concentration; 49% and 87% at 100 mg/kg concentration within 72 h, respectively. The OPs insecticide degrading gene opdA and opd was found in strain BHUJP-P3 and BHUJP-P4, respectively. The multifarious biological activities of strain BHUJP-P3 and BHUJP-P4 showed maximum tolerance against insecticide, and minimum reduction in P-solubilisation, IAA, siderophore and HCN production for plant growth promotion and biological control under insecticide stress. Thus, these novel isolates may be used as biodegradation of organophosphate insecticide and plant growth promoting bacterial (PGPB) inoculum for enhancing seed germination of vegetables under stress insecticide. These novel strains will be environment friendly, socially acceptable and economically viable.

Metal-organic and covalent organic frameworks as single-site catalysts

Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions.

Plant growth promoting rhizobia: challenges and opportunities

Modern agriculture faces challenges, such as loss of soil fertility, fluctuating climatic factors and increasing pathogen and pest attacks. Sustainability and environmental safety of agricultural production relies on eco-friendly approaches like biofertilizers, biopesticides and crop residue return. The multiplicity of beneficial effects of microbial inoculants, particularly plant growth promoters (PGP), emphasizes the need for further strengthening the research and their use in modern agriculture. PGP inhabit the rhizosphere for nutrients from plant root exudates. By reaction, they help in (1) increased plant growth through soil nutrient enrichment by nitrogen fixation, phosphate solubilization, siderophore production and phytohormones production (2) increased plant protection by influencing cellulase, protease, lipase and β-1,3 glucanase productions and enhance plant defense by triggering induced systemic resistance through lipopolysaccharides, flagella, homoserine lactones, acetoin and butanediol against pests and pathogens. In addition, the PGP microbes contain useful variation for tolerating abiotic stresses like extremes of temperature, pH, salinity and drought; heavy metal and pesticide pollution. Seeking such tolerant PGP microbes is expected to offer enhanced plant growth and yield even under a combination of stresses. This review summarizes the PGP related research and its benefits, and highlights the benefits of PGP rhizobia belonging to the family Rhizobiaceae, Phyllobacteriaceae and Bradyrhizobiaceae.

Isolation, Identification, and Characterization of an Organophosphorous Pesticide Degrading Bacterium, Enterobacter ludwigii M2

Strain M2 which can degrade organophosphorus pesticide residues was isolated from the soil. It could tolerate concentrations up to 500mg/L of methyl parathion, 500mg/L of chlorpyrifos and 1000mg/L of dimethoate in mineral salt medium containing 0.5% sucrose. In the soil test, strain M2 could degrade 93% of methyl parathion in the soil within 32 days, 71% of chlorpyrifos within 54 days. The degradation rate of strain M2 is much greater than that of natural microorganisms, soil adsorption and the capacity of natural degradation. Strain M2 was identified as a pesticide-degrading strain ofEnterobacter ludwigiiaccording to phenotype, biochemical properties and 16S rDNA sequence analysis. The type strain was M2 deposited in China General Microbiological Culture Collection Center on June 8, 2009 and the collection number is CGMCC NO.3092.

Isolation and characterization of novel phorate-degrading bacterial species from agricultural soil

Based upon 16S rDNA sequence homology, 15 phorate-degrading bacteria isolated from sugarcane field soils by selective enrichment were identified to be different species of Bacillus, Pseudomonas, Brevibacterium, and Staphylococcus. Relative phorate degradation in a mineral salt medium containing phorate (50 μg ml(-1)) as sole carbon source established that all the bacterial species could actively degrade more than 97 % phorate during 21 days. Three of these species viz. Bacillus aerophilus strain IMBL 4.1, Brevibacterium frigoritolerans strain IMBL 2.1, and Pseudomonas fulva strain IMBL 5.1 were found to be most active phorate metabolizers, degrading more than 96 % phorate during 2 days and 100 % phorate during 13 days. Qualitative analysis of phorate residues by gas liquid chromatography revealed complete metabolization of phorate without detectable accumulation of any known phorate metabolites. Phorate degradation by these bacterial species did not follow the first-order kinetics except the P. fulva strain IMBL 5.1 with half-life period (t1/2) ranging between 0.40 and 5.47 days.

A comparison of organophosphate degradation genes and bioremediation applications

Organophosphates (OPs) form the bulk of pesticides that are currently in use around the world accounting for more than 30% of the world market. They also form the core for many nerve-based warfare agents including sarin and soman. The widespread use and the resultant build-up of OP pesticides and chemical nerve agents has led to the development of major health problems due to their extremely toxic interaction with any biological system that encounters them. Growing concern over the accumulation of OP compounds in our food products, in the soils from which they are harvested and in wastewater run-off has fuelled a growing interest in microbial biotechnology that provides cheap, efficient OP detoxification to supplement expensive chemical methods. In this article, we review the current state of knowledge of OP pesticide and chemical agent degradation and attempt to clarify confusion over identification and nomenclature of two major families of OP-degrading enzymes through a comparison of their structure and function. The isolation, characterization, utilization and manipulation of the major detoxifying enzymes and the molecular basis of degradation of OP pesticides and chemical nerve agents are discussed as well as the achievements and technological advancements made towards the bioremediation of such compounds.

Mineralization of acephate, a recalcitrant organophosphate insecticide is initiated by a pseudomonad in environmental samples

An aerobic bacterium capable of breaking down the pesticide acephate (O,S-dimethyl acetyl phosphoramidothioic acid) was isolated from activated sludge collected from a pesticide manufacturing facility. A phylogenetic tree based on the 16 S rRNA gene sequence determined that the isolate lies within the Pseudomonads. The isolate was able to grow in the presence of acephate at concentrations up to 80 mM, with maximum growth at 40 mM. HPLC and LC-MS/MS analysis of spent medium from growth experiments and a resting cell assay detected the accumulation of methamidophos and acetate, suggesting initial hydrolysis of the amide linkage found between these two moieties. As expected, the rapid decline in acephate was coincident with the accumulation of methamidophos. Methamidophos concentrations were maintained over a period of days, without evidence of further metabolism or cell growth by the cultures. Considering this limitation, strains such as described in this work can promote the first step of acephate mineralization in soil microbial communities.

Ecotoxicological assessment of pesticides towards the plant growth promoting activities of Lentil (Lens esculentus)-specific Rhizobium sp. strain MRL3

This study was designed to evaluate the effect of the selected pesticides [herbicides (metribuzin and glyphosate), insecticides (imidacloprid and thiamethoxam) and fungicides (hexaconazole, metalaxyl and kitazin)] at the recommended and the higher dose rates on plant growth promoting traits of Rhizobium sp. strain MRL3 isolated from lentil-nodules. Strain MRL3 was explicitly selected owing to its high pesticide-tolerance ability and substantial production of indole acetic acid, siderophores (salicylic acid and 2, 3 dihydroxy benzoic acid), exo-polysaccharides, HCN and ammonia. A trend of pesticide-concentration dependent progressive-decline for plant growth promoting properties of Rhizobium sp. strain MRL3 was observed excluding exo-polysaccharides which was regularly augmented on exceeding the concentration of each tested pesticide from the recommended dose. Commonly, the maximum toxicity to plant growth promoting traits of Rhizobium was shown by glyphosate, imidacloprid and hexaconazole at three times the recommended rate among herbicides, insecticides and fungicides, respectively.

Effect of pesticides on plant growth promoting traits of greengram-symbiont, Bradyrhizobium sp. strain MRM6

The aim of this study was to investigate the toxicity of herbicides (metribuzin and glyphosate), insecticides (imidacloprid and thiamethoxam) and fungicides (hexaconazole, metalaxyl and kitazin) at the recommended and the higher dose rates on plant growth promoting activities of Bradyrhizobium sp. under in vitro conditions. The Bradyrhizobium sp. strain MRM6 was isolated from nodules of greengram plants. Pesticide-concentration dependent progressive-decline was observed in plant growth promoting traits of the strain MRM6 apart from exo-polysaccharides which increased consistently on increasing pesticide concentrations. Generally, the highest toxicity to plant growth promoting characteristics of the Bradyrhizobium sp. strain MRM6 was observed when the strain MRM6 was grown with three times the recommended field rates of glyphosate, imidacloprid and hexaconazole.

Isolation and characterization of a phorate degrading bacterium

AIMS

To study the degradation of phorate by a bacterium isolated from phorate-contaminated sites.

METHODS AND RESULTS

Ralstonia eutropha strain AAJ1 isolated from soil was found to degrade phorate (supplied as sole carbon source) upto 85% in 10 days in liquid medium. Half-life (t((1/2))) of phorate in the liquid medium in control (uninoculated) and in experimental (inoculated with R. eutropha, strain AAJ1) samples was recorded as 36.49 and 6.29 days, respectively. Kinetics revealed that phorate degradation depends on time and the reaction follows the first order kinetics. Diethyl dithiophosphate was one of the degradation products, which is markedly less toxic than the parent compound; other degradation products included phorate sulfoxide and phorate sulfone. Release of inorganic phosphates and sulfates indicated the potential of the isolate to further degrade the above-mentioned metabolites to simpler forms. The strain was also found to poses phosphomonoesterase and phosphodiesterase enzymatic activity, which are involved in biodegradation of organophosphorus compounds.

CONCLUSIONS

Ralstonia eutropha AAJ1 could degrade and detoxify phorate upto 85% in 10 days in laboratory conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The isolate has the potential to be utilized for remediation of phorate-contaminated water and soil.

Isolation and characterization of a profenofos degrading bacterium

Profenofos, a well known organophosphate pesticide, has been in agricultural use over the last two decades for controlling Lepidopteron pests of cotton and tobacco crops. In this study, a bacterial strain, OW, was isolated from a long term profenofos exposed soil by an enrichment technique, and its ability to degrade profenofos was determined using gas chromatography. The isolated strain OW was identified as Pseudomonas aeruginosa according to its physiological and biochemical properties, and the analysis of its 16S rRNA gene sequence. The strain grew well at pH 5.5-7.2 with a broad temperature profile. Bioremediation of profenofos-contaminated soil was examined using soil treated with 200 microg/g profenofos, which resulted in a higher degradation rate than control soils without inoculation. In a mineral salt medium (FTW), removal in the level of profenofos of 86.81% was obtained within 48 h of incubation. The intermediates of profenofos metabolism indicated that the degradation occurred through a hydrolysis mechanism, and one of the metabolites was found to be 4 bromo-2-cholorophenol (BCP) which in turn was also mineralized by the strain. The results of this study highlighted the potentiality of P aeruginosa as a biodegrader which could be used for the bioremediation of profenofos contaminated soil.

The reaction mechanism of paraoxon hydrolysis by phosphotriesterase from combined QM/MM simulations

Molecular dynamics simulations employing combined quantum mechanical and molecular mechanical (QM/MM) potentials have been carried out to investigate the reaction mechanism of the hydrolysis of paraoxon by phosphotriesterase (PTE). We used a dual-level QM/MM approach that synthesizes accurate results from high-level electronic structure calculations with computational efficiency of semiempirical QM/MM potentials for free energy simulations. In particular, the intrinsic (gas-phase) energies of the active site in the QM region are determined by using density functional theory (B3LYP) and second-order Møller-Plesset perturbation theory (MP2) and the molecular dynamics free energy simulations are performed by using the mixed AM1:CHARMM potential. The simulation results suggest a revised mechanism for the phosphotriester hydrolysis mechanism by PTE. The reaction free energy profile is mirrored by structural motions of the binuclear metal center in the active site. The two zinc ions occupy a compact conformation with an average zinc-zinc distance of 3.5 +/- 0.1 A in the Michaelis complex, whereas it is elongated to 5.3 +/- 0.3 A at the transition state and product state. The substrate is loosely bound to the more exposed zinc ion (Znbeta2+) at an average distance of 3.8 A +/- 0.3 A. The P=O bond of the substrate paraoxon is activated by adopting a tight coordination to the Znbeta2+, releasing the coordinate to the bridging hydroxide ion and increasing its nucleophilicity. It was also found that a water molecule enters into the binding pocket of the loosely bound binuclear center, originally occupied by the nucleophilic hydroxide ion. We suggest that the proton of this water molecule is taken up by His254 at low pH or released to the solvent at high pH, resulting in a hydroxide ion that pulls the Znbeta2+ ion closer to form the compact configuration and restores the resting state of the enzyme.

CYP201A2, a cytochrome P450 from Rhodopseudomonas palustris, plays a key role in the biodegradation of tributyl phosphate

Tributyl phosphate (TBP) is a toxic organophosphorous compound widely used in nuclear fuel processing and chemical industries. Rhodopseudomonas palustris, one of the most metabolically versatile photosynthetic bacteria, is shown here to degrade TBP efficiently under photosynthetic conditions. This study shows that this O(2)- and NADPH/FMNH(2)-dependent process was also catalyzed when TBP was incubated with membrane-associated proteins extracted from this strain. The effects of several regulators of cytochrome P450 activity on the TBP consumption suggest a key role for a cytochrome P450 in this process. Disruption of the rpa0241 gene encoding a putative cytochrome P450 led to a 60% decrease of the TBP catabolism, whereas reintroducing the gene in the mutant restored the wild-type phenotype. The rpa0241 gene was expressed and purified in Escherichia coli. Characterization by UV-visible spectroscopy of the purified recombinant membrane-bound protein (CYP201A2) encoded by the rpa0241 gene revealed typical spectral characteristics of cytochrome P450 with a large spin state change of the heme iron associated with binding of TBP (K (d) approximately 65 microM). It is proposed that CYP201A2 catalyzes the initial step of the biodegradation process of TBP.

Synthesis of [3-(3-chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2lambda5- benzo[e][1,3,2]oxazaphosphinin-2-yl]-(aryl/alkyl) methanols and their bioactivity on sugarcane smut

Synthesis of some new substituted [3-(3-chloro-4-fluorophenyl)-2-oxo-3,4-dihydro-2H-2lambda(5)-benzo[e][1,3,2]oxazaphosphinin-2-yl]-(aryl/alkyl)methanols (7a-k) based on the Pudovick reaction was accomplished in the presence of niobium pentoxide (Nb(2)O(5)) without using an external chiral ligand. Nb(2)O(5) appears to form the metal complex intermediate catalyst system (6) by reacting with 3-(3-chloro-4-fluoro-phenyl)-3,4-dihydrobenzo[e][1,3,2]oxazaphosphinine-2-oxide (4), which not only directs the Pudovick addition reactions of aldehyde but also increases the yields and purity of the products. These compounds exhibited a lethal effect on whip smut of sugarcane and were degraded in the environment in the presence of bacteria and fungi to nontoxic phosphate residues that act as possible plant nutrients. Thus, a new class of benzooxazaphosphininyl methanol derivatives that act in synergy both as antipathogens and as plant nutrients in the environment have been discovered.

Tributyl phosphate degradation by Rhodopseudomonas palustris and other photosynthetic bacteria

Tributyl phosphate (TBP) is widely used in nuclear fuel processing and other waste generating chemical industries. Although TBP is bacteriostatic, some microbes are resistant to it and may degrade it. Under dark aerobiosis, purple non-sulfur photosynthetic bacteria degraded up to 0.6 mM TBP, initially present at 2 mM, within 3 weeks and under photosynthetic conditions, Rhodopseudomonas palustris degraded 1.6 mM TBP within 3 weeks. The curing of the Rhodopseudomonas palustris endogenous plasmid demonstrated that the genes involved in the TBP degradation are chromosomal.

An inducible Streptomyces gene cluster involved in aromatic compound metabolism

Streptomyces setonii (ATCC 39116) is a thermophilic soil actinomycete capable of degrading single aromatic compounds including phenol and benzoate via the ortho-cleavage pathway. Previously, a 6.3-kb S. setonii DNA fragment containing a thermophilic catechol 1,2-dioxygenase (C12O) gene was isolated and functionally overexpressed in Escherichia coli (An et al., FEMS Microbiol. Lett. 195 (2001) 17-22). Here the 6.3-kb S. setonii DNA fragment was shown to be organized into two putative divergently transcribed gene clusters with six complete and one incomplete open reading frames (ORFs). The first cluster with three ORFs showed homologies to previously known benA, benB, and benC, implying it is a part of the benzoate catabolic operon. The second cluster revealed an ortho-cleavage catechol catabolic operon with three translationally coupled ORFs (in order): catR, a putative LysR-type regulatory gene; catB, a muconate cycloisomerase gene; catA, a C12O gene. Each of these individually cloned ORFs was expressed in E. coli and identified as a distinct protein. The expression of the cloned S. setonii catechol operon was induced in Streptomyces lividans by specific single aromatic compounds including catechol, phenol, and 4-chlorophenol. A similar induction pattern was also observed using a luciferase gene-fused reporter system.

Degradation of juvenile hormone analog by soil microbial isolates

Juvenoids are efficient pesticides with relatively low toxicity to humans. However, few studies have evaluated the effect of degradation by soil microorganisms on their toxicity. The effects of bacterial, fungal and yeast isolates on aerobic decomposition of ethyl N-[2-[4-(2,2-ethylenedioxy-1-cyclohexylmethyl)phenoxy]ethyl] carbamate during eight weeks were determined. The effect of different concentration of glucose on their degradation activity is also analyzed.

Biomineralization of an organophosphorus pesticide, Monocrotophos, by soil bacteria

AIMS

To study biomineralization of Monocrotophos (MCP) and identify the metabolites formed during biodegradation.

METHODS AND RESULTS

Two cultures, namely Arthrobacter atrocyaneus MCM B-425 and Bacillus megaterium MCM B-423, were isolated by enrichment and adaptation culture technique from soil exposed to MCP. The isolates were able to degrade MCP to the extent of 93% and 83%, respectively, from synthetic medium containing MCP at the concentration of 1000 mg x l(-1), within 8 d, under shake culture condition at 30 degrees C. The cultures degraded MCP to carbon dioxide, ammonia and phosphates through formation of one unknown compound--Metabolite I, valeric or acetic acid and methylamine, as intermediate metabolites. The enzymes phosphatase and esterase, reported to be involved in biodegradation of organophosphorus compounds, were detected in both the organisms.

CONCLUSIONS

Arthrobacter atrocyaneus MCM B-425 and B. megaterium MCM B-423 isolated from soil exposed to MCP were able to mineralize MCP to carbon dioxide, ammonia and phosphates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Pathway for biodegradation of MCP in plants and animals has been reported. A microbial metabolic pathway of degradation involving phosphatase and esterase enzymes has been proposed. The microbial cultures could be used for bioremediation of wastewater or soil contaminated with Monocrotophos.

Plasmid-mediated dimethoate degradation in Pseudomonas aeruginosa MCMB-427

AIMS

To investigate the genetics of dimethoate degradation in Pseudomonas aeruginosa MCMB-427.

METHODS AND RESULTS

Pseudomonas aeruginosa MCMB-427 demonstrated the ability to degrade dimethoate, a synthetic organophosphate insecticide. Total DNA preparation of MCMB-427 revealed the presence of a 6.6 kbp plasmid (designated as pDMD427). Escherichia coli NovaBlue transformed with plasmid pDMD427 subsequently acquired the ability to degrade dimethoate. Curing of the plasmid by plumbagin or ethidium bromide resulted in the loss of ability of MCMB-427 to degrade dimethoate. Plasmid pDMD427 was stable in MCMB-427 over 20 passages without selection. Genes encoding resistance to norfloxacin and cobalt were also located on plasmid pDMD427.

CONCLUSION

The ability of Ps. aeruginosa MCMB-427 to degrade dimethoate is plasmid-mediated and transferable to other strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

As far as is known, this is the first report of plasmid-mediated dimethoate biodegradation. This study contributes significantly towards an understanding of the genetics of bacterial dimethoate degradation.

Cloning and expression of thermophilic catechol 1,2-dioxygenase gene (catA) from Streptomyces setonii

Streptomyces setonii (ATCC 39116) degrades various single aromatic compounds such as phenol or benzoate via an ortho-cleavage pathway using catechol 1,2-dioxygenase (C12O). A PCR using degenerate primers based on the conserved regions of known C12O-encoding genes amplified a 0.45-kbp DNA fragment from S. setonii total DNA. A Southern hybridization analysis and size-selected DNA library screening using the 0.45-kbp PCR product as a probe led to the isolation of a 6.4-kbp S. setonii DNA fragment, from which the C12O-encoding genetic locus was found to be located within a 1.4-kbp DNA fragment. A complete nucleotide sequencing analysis of the 1.4-kbp DNA fragment revealed a 0.84-kbp open reading frame, which showed a strong overall amino acid similarity to the known high-G+C Gram-positive (but significantly less to the Gram-negative) bacterial mesophilic C12Os. The heterologous expression of the cloned 1.4-kbp DNA fragment in Escherichia coli demonstrated that this C12O possessed a thermophilic activity within a broad temperature range (up to 65 degrees C) and showed a higher activity against 3-methylcatechol than catechol or 4-methylcatechol, but no activity against protocatechuate.

Degradation of pesticides by actinomycetes

Actinomycetes have considerable potential for the biotransformation and biodegradation of pesticides. Members of this group of Gram-positive bacteria have been found to degrade pesticides with widely different chemical structures, including organochlorines, s-triazines, triazinones, carbamates, organophosphates, organophosphonates, acetanilides, and sulfonylureas. A limited number of these xenobiotic pesticides can be mineralized by single isolates, but often consortia of bacteria are required for complete degradation. Cometabolism of pesticides is frequently observed within this group of bacteria. When compared with pesticide degradation by Gram-negative bacteria, much less information about molecular mechanisms involved in biotransformations of pesticides by actinomycetes is available. Progress in this area has been seriously hampered by a lack of suitable molecular genetic tools for most representatives of this major group of soil bacteria. Overcoming this constraint would enable a better exploitation of the biodegradation and biotransformation abilities of actinomycetes for applications such as bioremediation and construction of transgenic herbicide-resistant crops.

Biodegradation of the herbicide Diuron in soil by indigenous actinomycetes

Three actinomycete strains isolated from soil treated with 2,4-D were able to degrade the herbicide Diuron in vitro. Strain CCT 4916 was the most efficient, degrading up to 37% of applied Diuron (100 mg Kg-1 soil) in 7 days, as measured by HPLC and UV/VIS spectroscopy. All strains showed protease and urease activity; intracellular activity of metapyrocatechase and pyrocatechase were not found. Actinomycete strain CCT 4916 produced manganese peroxidase, which could be potentially related to degradation of Diuron.