Pathway for degradation of 2-chloro-4-nitrophenol in Arthrobacter sp. SJCon

Addition of carbon sources and nutrient salts can inhibit gangue acidification by changing microbial community structure

Acidic pollution from gangue oxidation has become a primary environmental problem in coal mining areas in China. The use of microorganisms to remediate acidic pollution in coal gangue piles has been indicated to be effective, but environmental differences and carbon sources in different mining areas have become important factors restricting microbial activity. Instead of the addition of new functional bacteria to gangue piles, carbon sources and nutrient salts were added to recently discharged gangue to enhance the activity of beneficial bacteria in the indigenous microbial community. The changes in pH and electrical conductivity (EC) of the gangue leachate as well as the composition and abundance of the functional microbial community on the surface of the gangue were analyzed by leaching simulation experiments and 16S rRNA sequencing. The results showed that the addition of a carbon source maintained the pH of the gangue leachate at 6.31~6.65 in 14 d, which was significantly higher than that of the control group, but the pH of the leachate decreased significantly after the addition of the carbon source was stopped. The most effective treatment is adding a low concentration of nutrient salt (20% concentration) and sodium lactate (0.02 g/L) to the gangue first, and then adding sodium lactate (0.1 mg/L) every 7 days. The addition of carbon sources and nutrient salts changed the microbial community composition on the surface of the gangue, and the species diversity index decreased. The dominant genera in the experimental group were Listeria, Arthrobacter, and Enterococcus. The functional gene types in the experimental and control groups were almost the same, but their relative abundance changed. The abundance of functional genes related to the sulfur cycle increased substantially in the experimental group, and the abundance of genes involved in the nitrogen and carbon cycles also increased, albeit to different degrees.

A two-component monooxygenase for continuous denitration and dechlorination of chlorinated 4-nitrophenol in Ensifer sp. strain 22-1

The environmental fates of chlorinated 4-nitrophenols, 2,6-dichloro-4-nitrophenol (2,6-DCNP) and 2-chloro-4-nitrophenol (2C4NP), mediated via microbial catabolism have attracted great attention due to their high toxicity and persistence in the environment. In this study, a strain of Ensifer sp. 22-1 that was capable of degrading both 2,6-DCNP and 2C4NP was isolated from a halogenated aromatic-contaminated soil sample. A gene cluster cnpBADCERM was predicted to be involved in the catabolism of 2,6-DCNP and 2C4NP based on genome sequence analysis. A two-component monooxygenase CnpAB, composed of an oxygenase component (CnpA) and a reductase component (CnpB), was confirmed to catalyze the continuous denitration and dechlorination of 2,6-DCNP and 2C4NP to 6-chlorohydroxyquinol (6-CHQ) and hydroxyquinol (HQ), respectively. Knockout of cnpA resulted in the complete loss of the capacity for strain 22-1 to degrade 2,6-DCNP and 2C4NP. Homologous modeling and docking showed that Val155~Ala159, Phe206~Pro209 and Phe446~Arg461 of CnpA participated in the formation of the FAD-binding pocket, and Arg101, Val155 and Asn447 formed hydrogen bonds with 2,6-DCNP/2C4NP in the substrate-binding pocket. This work characterized a new two-component monooxygenase for 2,6-DCNP and 2C4NP, and enriched our understanding of the degradation mechanism of chlorinated nitrophenols (CNPs) by microorganisms.

Microbial degradation kinetics and molecular mechanism of 2,6-dichloro-4-nitrophenol by a Cupriavidus strain

2,6-Dichloro-4-nitrophenol (2,6-DCNP) is an emerging chlorinated nitroaromatic pollutant, and its fate in the environment is an important question. However, microorganisms with the ability to utilize 2,6-DCNP have not been reported. In this study, Cupriavidus sp. CNP-8 having been previously reported to degrade various halogenated nitrophenols, was verified to be also capable of degrading 2,6-DCNP. Biodegradation kinetics assay showed that it degraded 2,6-DCNP with the specific growth rate of 0.124 h^-1, half saturation constant of 0.038 mM and inhibition constant of 0.42 mM. Real-time quantitative PCR analyses indicated that the hnp gene cluster was involved in the catabolism of 2,6-DCNP. The hnpA and hnpB gene products were purified to homogeneity by Ni-NTA chromatography. Enzymatic assays showed that HnpAB, a FAD-dependent two-component monooxygenase, converted 2,6-DCNP to 6-chlorohydroxyquinol with a K_m of 3.9 ± 1.4 μM and a k_cat/K_m of 0.12 ± 0.04 μΜ^-1 min^-1. As the oxygenase component encoding gene, hnpA is necessary for CNP-8 to grow on 2,6-DCNP by gene knockout and complementation. The phylogenetic analysis showed that the hnp cluster originated from the cluster involved in the catabolism of chlorophenols rather than nitrophenols. To our knowledge, CNP-8 is the first bacterium with the ability to utilize 2,6-DCNP, and this study fills a gap in the microbial degradation mechanism of this pollutant at the molecular, biochemical and genetic levels. Moreover, strain CNP-8 could degrade three chlorinated nitrophenols rapidly from the synthetic wastewater, indicating its potential in the bioremediation of chlorinated nitrophenols polluted environments.

Environmental persistence, hazard, and mitigation challenges of nitroaromatic compounds

Nitroaromatic compounds (NACs) are extensively used in different industries and are synthesized in large quantity due to their heavy demand worldwide. The broad use of NACs poses a serious pollution threat. The treatment processes used for the removal of NACs are not effective and sustainable, leading to their release into the environment. The nitro group attached to benzene ring makes the compounds recalcitrant due to which they persist in the environment. Being hazardous to human as well as other living organisms, NACs are listed in the USEPA's priority pollutant group. This review provides updated information on the sources of NACs, prevalence in different environmental matrices, and recent developments in methods of their detection, with emphasis on current trends as well as future prospects. The harmful effects of NACs due to exposure through different routes are also highlighted. Further, the technologies reported for the treatment of NACs, including physico-chemical and biological methods, and the challenges faced for their effective implementation are discussed. Thus, the review discusses relevant issues in detail making suitable recommendations, which can be helpful in guiding further research in this subject.

Biodegradation of persistent environmental pollutants by Arthrobacter sp

Persistent environmental pollutants are a growing problem around the world. The effective control of the pollutants is of great significance for human health. Some microbes, especially Arthrobacter, can degrade pollutants into nontoxic substances in various ways. Here, we review the biological properties of Arthrobacter adapting to a variety of environmental stresses, including starvation, hypertonic and hypotonic condition, oxidative stress, heavy metal stress, and low-temperature stress. Furthermore, we categorized the Arthrobacter species that can degrade triazines, organophosphorus, alkaloids, benzene, and its derivatives. Metabolic pathways behind the various biodegradation processes are further discussed. This review will be a helpful reference for comprehensive utilization of Arthrobacter species to tackle environmental pollutants.

Biodegradation of 2-chloro-4-nitrophenol via a hydroxyquinol pathway by a Gram-negative bacterium, Cupriavidus sp. strain CNP-8

Cupriavidus sp. strain CNP-8 isolated from a pesticide-contaminated soil was able to utilize 2-chloro-4-nitrophenol (2C4NP) as a sole source of carbon, nitrogen and energy, together with the release of nitrite and chloride ions. It could degrade 2C4NP at temperatures from 20 to 40 °C and at pH values from 5 to 10, and degrade 2C4NP as high as 1.6 mM. Kinetics assay showed that biodegradation of 2C4NP followed Haldane substrate inhibition model, with the maximum specific growth rate (μ_max) of 0.148/h, half saturation constant (K_s) of 0.022 mM and substrate inhibition constant (K_i) of 0.72 mM. Strain CNP-8 was proposed to degrade 2C4NP with hydroxyquinol (1,2,4-benzenetriol, BT) as the ring-cleavage substrate. The 2C4NP catabolic pathway in strain CNP-8 is significant from those reported in other Gram-negative 2C4NP utilizers. Enzymatic assay indicated that the monooxygenase initiating 2C4NP catabolism had different substrates specificity compared with previously reported 2C4NP monooxygenations. Capillary assays showed that strain CNP-8 exhibited metabolism-dependent chemotactic response toward 2C4NP at the optimum concentration of 0.5 mM with a maximum chemotaxis index of 37.5. Furthermore, microcosm studies demonstrated that strain CNP-8, especially the pre-induced cells, could remove 2C4NP rapidly from the 2C4NP-contaminated soil. Considering its adaptability to pH and temperature fluctuations and great degradation efficiency against 2C4NP, strain CNP-8 could be a promising candidate for the bioremediation of 2C4NP-contaminated sites.

Recent advances in degradation of chloronitrophenols

Chloronitrophenols (CNPs) constitute a group of environmental pollutants that are widely distributed in our surrounding environment due to human based activities. This group of chemicals is highly toxic to living beings due to its mutagenic and carcinogenic nature. Examples include 2-chloro-4-nitrophenol, 4-chloro-2-nitrophenol, 2-chloro-5-nitrophenol, 4-chloro-3-nitrophenol and 2,6-dichloro-4-nitrophenol. Several methods including advanced oxidation processes, adsorption and bacterial degradation have been used for degradation of CNPs. Among, bacterial degradation is an eco-friendly and effective way to degrade CNPs. Several bacterial metabolic pathways have been proposed for degradation of CNPs and their genes and enzymes have been identified in bacteria. These bacteria were able to degrade CNPs in broth culture and soil. Therefore, CNPs-degrading bacteria are suitable candidates for bioremediation of CNPs-contaminated sites. Few CNP-degrading bacteria exhibited chemotaxis towards CNPs to enhance their biodegradation. The present review summarizes recent progress in degradation of CNPs.

Genetic and Biochemical Characterization of 2-Chloro-5-Nitrophenol Degradation in a Newly Isolated Bacterium, Cupriavidus sp. Strain CNP-8

Compound 2-chloro-5-nitrophenol (2C5NP) is a typical chlorinated nitroaromatic pollutant. To date, the bacteria with the ability to degrade 2C5NP are rare, and the molecular mechanism of 2C5NP degradation remains unknown. In this study, Cupriavidus sp. strain CNP-8 utilizing 2-chloro-5-nitrophenol (2C5NP) and meta-nitrophenol (MNP) via partial reductive pathways was isolated from pesticide-contaminated soil. Biodegradation kinetic analysis indicated that 2C5NP degradation by this strain was concentration dependent, with a maximum specific degradation rate of 21.2 ± 2.3 μM h⁻¹. Transcriptional analysis showed that the mnp genes are up-regulated in both 2C5NP- and MNP-induced strain CNP-8. Two Mnp proteins were purified to homogeneity by Ni-NTA affinity chromatography. In addition to catalyzing the reduction of MNP, MnpA, a NADPH-dependent nitroreductase, also catalyzes the partial reduction of 2C5NP to 2-chloro-5-hydroxylaminophenol via 2-chloro-5-nitrosophenol, which was firstly identified as an intermediate of 2C5NP catabolism. MnpC, an aminohydroquinone dioxygenase, is likely responsible for the ring-cleavage reaction of 2C5NP degradation. Gene knockout and complementation indicated that mnpA is necessary for both 2C5NP and MNP catabolism. To our knowledge, strain CNP-8 is the second 2C5NP-utilizing bacterium, and this is the first report of the molecular mechanism of microbial 2C5NP degradation.

Biochemical Characterization of 3-Methyl-4-nitrophenol Degradation in Burkholderia sp. Strain SJ98

Several strains have been reported to grow on 3-methyl-4-nitrophenol (3M4NP), the primary breakdown product of the excessively used insecticide fenitrothion. However, the microbial degradation of 3M4NP at molecular and biochemical levels remains unknown. Here, methyl-1,4-benzoquinone (MBQ) and methylhydroquinone (MHQ), rather than catechol proposed previously, were identified as the intermediates before ring cleavage during 3M4NP degradation by Burkholderia sp. strain SJ98. Real-time quantitative PCR analysis indicated that the pnpABA1CDEF cluster involved in para-nitrophenol (PNP) and 2-chloro-4-nitrophenol (2C4NP) catabolism was also likely responsible for 3M4NP degradation in this strain. Purified PNP 4-monooxygenase (PnpA) is able to catalyze the monooxygenation of 3M4NP to MBQ and exhibited an apparent K_m value of 20.3 ± 2.54 μM for 3M4NP, and pnpA is absolutely necessary for the catabolism of 3M4NP by gene knock-out and complementation. PnpB, a 1,4-benzoquinone reductase catalyzes the reduction of MBQ to MHQ, and also found to enhance PnpA activity in vitro in the conversion of 3M4NP to MBQ. By sequential catalysis assays, PnpCD, PnpE, and PnpF were likely involved in the lower pathway of 3M4NP catabolism. Although NpcCD, NpcE, and NpcF are able to catalyze the sequential conversion of MHQ in vitro, these enzymes are unlikely involved in 3M4NP catabolism because their coding genes were not upregulated by 3M4NP induction in vivo. These results revealed that the enzymes involved in PNP and 2C4NP catabolism were also responsible for 3M4NP degradation in strain SJ98. This fills a gap in our understanding of the microbial degradation of 3M4NP at molecular and biochemical levels and also provides another example to illustrate the adaptive flexibility in microbial catabolism for structurally similar compounds.

Degradation of Swainsonine by the NADP-Dependent Alcohol Dehydrogenase A1R6C3 in Arthrobacter sp. HW08

Swainsonine is an indolizidine alkaloid that has been found in locoweeds and some fungi. Our previous study demonstrated that Arthrobacter sp. HW08 or its crude enzyme extract could degrade swainsonie efficiently. However, the mechanism of swainsonine degradation in bacteria remains unclear. In this study, we used label-free quantitative proteomics method based on liquid chromatography-electrospray ionization-tandem mass spectrometry to dissect the mechanism of swainsonine biodegradation by Arthrobacter sp. HW08. The results showed that 129 differentially expressed proteins were relevant to swainsonine degradation. These differentially expressed proteins were mostly related to the biological process of metabolism and the molecular function of catalytic activity. Among the 129 differentially expressed proteins, putative sugar phosphate isomerase/epimerase A1R5X7, Acetyl-CoA acetyltransferase A0JZ95, and nicotinamide adenine dinucleotide phosphate (NADP)-dependent alcohol dehydrogenase A1R6C3 were found to contribute to the swainsonine degradation. Notably, NADP-dependent alcohol dehyrodgenase A1R6C3 appeared to play a major role in degrading swainsonine, but not as much as Arthrobacter sp. HW08 did. Collectively, our findings here provide insights to understand the mechanism of swainsonine degradation in bacteria.

A Two-Component para-Nitrophenol Monooxygenase Initiates a Novel 2-Chloro-4-Nitrophenol Catabolism Pathway in Rhodococcus imtechensis RKJ300

Rhodococcus imtechensis RKJ300 (DSM 45091) grows on 2-chloro-4-nitrophenol (2C4NP) and para-nitrophenol (PNP) as the sole carbon and nitrogen sources. In this study, by genetic and biochemical analyses, a novel 2C4NP catabolic pathway different from those of all other 2C4NP utilizers was identified with hydroxyquinol (hydroxy-1,4-hydroquinone or 1,2,4-benzenetriol [BT]) as the ring cleavage substrate. Real-time quantitative PCR analysis indicated that the pnp cluster located in three operons is likely involved in the catabolism of both 2C4NP and PNP. The oxygenase component (PnpA1) and reductase component (PnpA2) of the two-component PNP monooxygenase were expressed and purified to homogeneity, respectively. The identification of chlorohydroquinone (CHQ) and BT during 2C4NP degradation catalyzed by PnpA1A2 indicated that PnpA1A2 catalyzes the sequential denitration and dechlorination of 2C4NP to BT and catalyzes the conversion of PNP to BT. Genetic analyses revealed that pnpA1 plays an essential role in both 2C4NP and PNP degradations by gene knockout and complementation. In addition to catalyzing the oxidation of CHQ to BT, PnpA1A2 was also found to be able to catalyze the hydroxylation of hydroquinone (HQ) to BT, revealing the probable fate of HQ that remains unclear in PNP catabolism by Gram-positive bacteria. This study fills a gap in our knowledge of the 2C4NP degradation mechanism in Gram-positive bacteria and also enhances our understanding of the genetic and biochemical diversity of 2C4NP catabolism.

Biotransformation and chemotaxis of 4-chloro-2-nitrophenol by Pseudomonas sp. JHN

Pseudomonas sp. JHN decolourized and biotransformed 4-chloro-2-nitrophenol (4C2NP) in the presence of additional carbon source. The effect of the various concentrations of the 4C2NP was studied on the decolourization of 4C2NP by Pseudomonas sp. JHN. It was observed that strain JHN decolourized and biotransformed 4C2NP up to concentration of 0.6 mM. Gas chromatography and gas chromatography-mass spectrometry detected 5-chloro-2-methylbenzoxazole as a major metabolite of the co-metabolism of 4C2NP. Furthermore, strain JHN exhibits positive chemotaxis toward 4C2NP based on the drop plate and capillary assays. This is the first report of the chemotaxis toward 4C2NP by any bacterium.

The gene cluster for para-nitrophenol catabolism is responsible for 2-chloro-4-nitrophenol degradation in Burkholderia sp. strain SJ98

Burkholderia sp. strain SJ98 (DSM 23195) utilizes 2-chloro-4-nitrophenol (2C4NP) or para-nitrophenol (PNP) as a sole source of carbon and energy. Here, by genetic and biochemical analyses, a 2C4NP catabolic pathway different from those of all other 2C4NP utilizers was identified with chloro-1,4-benzoquinone (CBQ) as an intermediate. Reverse transcription-PCR analysis showed that all of the pnp genes in the pnpABA1CDEF cluster were located in a single operon, which is significantly different from the genetic organization of all other previously reported PNP degradation gene clusters, in which the structural genes were located in three different operons. All of the Pnp proteins were purified to homogeneity as His-tagged proteins. PnpA, a PNP 4-monooxygenase, was found to be able to catalyze the monooxygenation of 2C4NP to CBQ. PnpB, a 1,4-benzoquinone reductase, has the ability to catalyze the reduction of CBQ to chlorohydroquinone. Moreover, PnpB is also able to enhance PnpA activity in vitro in the conversion of 2C4NP to CBQ. Genetic analyses indicated that pnpA plays an essential role in the degradation of both 2C4NP and PNP by gene knockout and complementation. In addition to being responsible for the lower pathway of PNP catabolism, PnpCD, PnpE, and PnpF were also found to be likely involved in that of 2C4NP catabolism. These results indicated that the catabolism of 2C4NP and that of PNP share the same gene cluster in strain SJ98. These findings fill a gap in our understanding of the microbial degradation of 2C4NP at the molecular and biochemical levels.

Degradation of 4-chloro-3-nitrophenol via a novel intermediate, 4-chlororesorcinol by Pseudomonas sp. JHN

A 4-chloro-3-nitrophenol (4C3NP)-mineralizing bacterium, Pseudomonas sp. JHN was isolated from a waste water sample collected from a chemically-contaminated area, India by an enrichment method. Pseudomonas sp. JHN utilized 4C3NP as a sole carbon and energy source and degraded it with the release of stoichiometric amounts of chloride and nitrite ions. Gas chromatography and gas chromatography-mass spectrometry detected 4-chlororesorcinol as a major metabolite of the 4C3NP degradation pathway. Inhibition studies using 2,2′-dipyridyl showed that 4-chlororesorcinol is a terminal aromatic compound in the degradation pathway of 4C3NP. The activity for 4C3NP-monooxygenase was detected in the crude extracts of the 4C3NP-induced JHN cells that confirmed the formation of 4-chlororesorcinol from 4C3NP. The capillary assay showed that Pseudomonas sp. JHN exhibited chemotaxis toward 4C3NP. The bioremediation capability of Pseudomonas sp. JHN was monitored to carry out the microcosm experiments using sterile and non-sterile soils spiked with 4C3NP. Strain JHN degraded 4C3NP in sterile and non-sterile soil with same degradation rates. This is the first report of (i) bacterial degradation and bioremediation of 4C3NP, (ii) formation of 4-chlororesorcinol in the degradation pathway of 4C3NP, (iii) bacterial chemotaxis toward 4C3NP.

Bacterial degradation of chlorophenols and their derivatives

Chlorophenols (CPs) and their derivatives are persistent environmental pollutants which are used in the manufacture of dyes, drugs, pesticides and other industrial products. CPs, which include monochlorophenols, polychlorophenols, chloronitrophenols, chloroaminophenols and chloromethylphenols, are highly toxic to living beings due to their carcinogenic, mutagenic and cytotoxic properties. Several physico-chemical and biological methods have been used for removal of CPs from the environment. Bacterial degradation has been considered a cost-effective and eco-friendly method of removing CPs from the environment. Several bacteria that use CPs as their sole carbon and energy sources have been isolated and characterized. Additionally, the metabolic pathways for degradation of CPs have been studied in bacteria and the genes and enzymes involved in the degradation of various CPs have been identified and characterized. This review describes the biochemical and genetic basis of the degradation of CPs and their derivatives.

Bacterial degradation of nitrophenols and their derivatives

This review intends to provide an overview of bacterial degradation of nitrophenols (NPs) and their derivatives. The main scientific focus is on biochemical and genetic characterization of bacterial degradation of NPs. Other aspects such as bioremediation and chemotaxis correlated with biodegradation of NPs are also discussed. This review will increase our current understanding of bacterial degradation of NPs and their derivatives.

Mutagenicity and genotoxicity of dicapthon insecticide

Mutagenic and genotoxic effects of dicapthon were investigated by using the bacterial reverse mutation assay in Salmonella typhimurium TA97, TA98, TA100 and TA102 strains with or without metabolic activation system (S9 mix), and chromosome aberrations (CAs), sister chromatid exchanges (SCEs), and micronucleus (MN) tests in human peripheral blood lymphocytes in vitro. Dicapthon was dissolved in dimethyl sulfoxide for all test systems. 0.1, 1, 10 and 100 μg/plate doses of dicapthon were found to be weakly mutagenic on S. typhimurium TA 98 without S9 mix. The human peripheral lymphocytes were treated with four experimental concentrations of dicapthon (25, 50, 100, and 200 μg/mL) for 24 and 48 h. Dicapthon increased the frequency of SCE only at the 100 μg/mL concentration for the 24 and 48 h applications. Dicapthon also induced abnormal cell frequency, CA/cell ratio and frequency of MN dose dependently for 24 and 48 h. Dicapthon showed a statistically significant cytotoxic effect by decreasing the mitotic index in all concentrations and a cytostatic effect by decreasing nuclear division index in 100 and 200 μg/mL concentrations for both treatment periods when compared with both untreated and solvent controls. These values decreased also in a dose dependent manner.

Draft Genome Sequence of the 2-Chloro-4-Nitrophenol-Degrading Bacterium Arthrobacter sp. Strain SJCon

We report the 4.39-Mb draft genome sequence of the 2-chloro-4-nitrophenol-degrading bacterium Arthrobacter sp. strain SJCon, isolated from a pesticide-contaminated site. The draft genome sequence of strain SJCon will be helpful in studying the genetic pathways involved in the degradation of several aromatic compounds.

Arthrobacter nitrophenolicus sp. nov. a new 2-chloro-4-nitrophenol degrading bacterium isolated from contaminated soil

Strain SJCon^T, a 2-chloro-4-nitrophenol (2C4NP) degrading bacterium, was isolated from soil collected from a pesticide-contaminated site in Punjab, India. The strain, which stained Gram positive, displayed a rod-coccus life cycle, and possessed a type A3_α peptidoglycan (l-Lys–l-Ala₃), MK-9(H2) as the major menaquinone, anteiso-C15 and iso-C15:0 as the major cellular fatty acids, and diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and a glycolipid as the major polar lipids, showed morphological and chemotaxonomic properties consistent with those reported for members of the genus Arthrobacter. Phylogenetic analysis of the 16S rRNA gene sequence of strain SJCon^T confirmed that it was a member of this genus with Arthrobacter globiformis DSM 20124^T being the closest relative (sequence similarity of 97 %). The DNA G + C content of strain SJCon^T was 69 ± 1 mol% and DNA homology with A. globiformis DSM 20124^T was 45 %, suggesting that strain SJCon^T represented a novel species of the genus Arthrobacter, which we have named Arthrobacter nitrophenolicus sp. nov The type strain is SJCon^T (=MTCC 10104^T =DSM 23165^T).

Review of advances in the thin layer chromatography of pesticides: 2010-2012

Techniques and applications of thin layer chromatography (planar chromatography) for the separation, detection, qualitative and quantitative determination, and preparative isolation of pesticides and their metabolites and some related pollutants are reviewed for the period from November 1, 2010 to November 1, 2012. Analyses are described for a variety of samples types and pesticide classes. In addition to references on residue analysis, studies such as pesticide structure - retention relationships, identification and characterization of natural and synthesized pesticides, metabolism, degradation, mobility, lipophilicity, and mechanism of action are covered.

Metabolism of 4-chloro-2-nitrophenol in a gram-positive bacterium, Exiguobacterium sp. PMA

Background

Chloronitrophenols (CNPs) are widely used in the synthesis of dyes, drugs and pesticides, and constitute a major group of environmental pollutants. 4-Chloro-2-nitrophenol (4C2NP) is an isomer of CNPs that has been detected in various industrial effluents. A number of physicochemical methods have been used for treatment of wastewater containing 4C2NP. These methods are not as effective as microbial degradation, however.

Results

A 4C2NP-degrading bacterium, Exiguobacterium sp. PMA, which uses 4C2NP as the sole carbon and energy source was isolated from a chemically-contaminated site in India. Exiguobacterium sp. PMA degraded 4C2NP with the release of stoichiometeric amounts of chloride and ammonium ions. The effects of different substrate concentrations and various inoculum sizes on degradation of 4C2NP were investigated. Exiguobacterium sp. PMA degraded 4C2NP up to a concentration of 0.6 mM. High performance liquid chromatography and gas chromatography–mass spectrometry identified 4-chloro-2-aminophenol (4C2AP) and 2-aminophenol (2AP) as possible metabolites of the 4C2NP degradation pathway. The crude extract of 4C2NP-induced PMA cells contained enzymatic activity for 4C2NP reductase and 4C2AP dehalogenase, suggesting the involvement of these enzymes in the degradation of 4C2NP. Microcosm studies using sterile and non-sterile soils spiked with 4C2NP were carried out to monitor the bioremediation potential of Exiguobacterium sp. PMA. The bioremediation of 4C2NP by Exiguobacterium sp. PMA was faster in non-sterilized soil than sterilized soil.

Conclusions

Our studies indicate that Exiguobacterium sp. PMA may be useful for the bioremediation of 4C2NP-contaminated sites. This is the first report of (i) the formation of 2AP in the 4C2NP degradation pathway by any bacterium and (iii) the bioremediation of 4C2NP by any bacterium.

Metabolism of 2-chloro-4-nitrophenol in a gram negative bacterium, Burkholderia sp. RKJ 800

A 2-Chloro-4-nitrophenol (2C4NP) degrading bacterial strain designated as RKJ 800 was isolated from a pesticide contaminated site of India by enrichment method and utilized 2C4NP as sole source of carbon and energy. The stoichiometric amounts of nitrite and chloride ions were detected during the degradation of 2C4NP. On the basis of thin layer chromatography, high performance liquid chromatography and gas chromatography-mass spectrometry, chlorohydroquinone (CHQ) and hydroquinone (HQ) were identified as major metabolites of the degradation pathway of 2C4NP. Manganese dependent HQ dioxygenase activity was observed in the crude extract of 2C4NP induced cells of the strain RKJ 800 that suggested the cleavage of the HQ to γ-hydroxymuconic semialdehyde. On the basis of the 16S rRNA gene sequencing, strain RKJ 800 was identified as a member of genus Burkholderia. Our studies clearly showed that Burkholderia sp. RKJ 800 degraded 2-chloro-4-nitrophenol via hydroquinone pathway. The pathway identified in a gram negative bacterium, Burkholderia sp. strain RKJ 800 was differed from previously reported 2C4NP degradation pathway in another gram-negative Burkholderia sp. SJ98. This is the first report of the formation of CHQ and HQ in the degradation of 2C4NP by any gram-negative bacteria. Laboratory-scale soil microcosm studies showed that strain RKJ 800 is a suitable candidate for bioremediation of 2C4NP contaminated sites.

Degradation of chlorinated nitroaromatic compounds

Chlorinated nitroaromatic compounds (CNAs) are persistent environmental pollutants that have been introduced into the environment due to the anthropogenic activities. Bacteria that utilize CNAs as the sole sources of carbon and energy have been isolated from different contaminated and non-contaminated sites. Microbial metabolism of CNAs has been studied, and several metabolic pathways for degradation of CNAs have been proposed. Detoxification and biotransformation of CNAs have also been studied in various fungi, actinomycetes and bacteria. Several physicochemical methods have been used for treatment of wastewater containing CNAs; however, these methods are not suitable for in situ bioremediation. This review describes the current scenario of the degradation of CNAs.