Kegg Pathway: Atrazine degradation

Water Res. 2009 Oct 4;
Klamerth N, Rizzo L, Malato S, Maldonado MI, Agüera A, Fernández-Alba AR

The degradation of 15 emerging contaminants (ECs) at low concentrations in simulated and real effluent of municipal wastewater treatment plant with photo-Fenton at unchanged pH and Fe=5mgL(-1) in a pilot-scale solar CPC reactor was studied. The degradation of those 15 compounds (Acetaminophen, Antipyrine, Atrazine, Caffeine, Carbamazepine, Diclofenac, Flumequine, Hydroxybiphenyl, Ibuprofen, Isoproturon, Ketorolac, Ofloxacin, Progesterone, Sulfamethoxazole and Triclosan), each with an initial concentration of 100mugL(-1), was found to depend on the presence of CO(3)(2-) and HCO(3)(-) (hydroxyl radicals scavengers) and on the type of water (simulated water, simulated effluent wastewater and real effluent wastewater), but is relatively independent of pH, the type of acid used for release of hydroxyl radicals scavengers and the initial H(2)O(2) concentration used. Toxicity tests with Vibrio fisheri showed that degradation of the compounds in real effluent wastewater led to toxicity increase.

Lett Appl Microbiol. 2009 Aug 22;
Fazlurrahman , Batra M, Pandey J, Suri CR, Jain RK

Abstract Aims: The aim of this study is to isolate and characterize organisms capable of utilizing high concentration Atrazine from the contaminated sites. Methods and Results: A selective enrichment was used for isolating Atrazine-degrading organisms from the contaminated sites resulting in isolation of an efficient Atrazine-degrading organism designated as strain MB-P1. On the basis of 16S rRNA gene sequencing, total cellular fatty acid analysis and physiological and biochemical tests, strain MB-P1 was identified as a member of genus Rhodococcus. High performance liquid chromatography was performed to identify the Atrazine degradation intermediates demonstrating that the degradation proceeds via formation of 'de-ethylAtrazine' and 'de-isopropylAtrazine'. Further, plasmid curing by SDS method showed Atrazine-degrading gene(s) to be plasmid-encoded. Conclusions: We have successfully isolated a Rhodococcus sp. strain MB-P1 which is capable of utilizing Atrazine as sole source of carbon and energy at very high concentrations of 1000 ppm. The pathway for degradation of Atrazine has also been determined. The metabolic gene(s) responsible for Atrazine degradation was found to be plasmid-encoded. Significance and Impact of the Study: Rhodococcus sp. strain MB-P1 could be used as an ideal model system for in-situ degradation and restoration of ecological niches which are heavily contaminated with Atrazine.

Int J Phytoremediation. 2009 Oct-Dec; 11(8): 664-91
Danh LT, Truong P, Mammucari R, Tran T, Foster N

Glasshouse and field studies showed that Vetiver grass can produce high biomass (>100t/ tha(-1) year(-1)) and highly tolerate extreme climatic variation such as prolonged drought, flood, submergence and temperatures (-15 degrees - 55 degrees C), soils high in acidity and alkalinity (pH 3.3-9.5), high levels of Al (85% saturation percentage), Mn (578 mg kg(-1)), soil salinity (ECse 47.5 dS m(-1)), sodicity (ESP 48%), anda wide range of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Zn). Vetiver can accumulate heavy metals, particularly lead (shoot 0.4% and root 1%) and zinc (shoot and root 1%). The majority of heavy metals are accumulated in roots thus suitable for phytostabilization, and for phytoextraction with addition of chelating agents. Vetiver can also absorb and promote biodegradation of organic wastes (2,4,6-trinitroluene, phenol, ethidium bromide, benzo[a]pyrene, Atrazine). Although Vetiver is not as effective as some other species in heavy metal accumulation, very few plants in the literature have a wide range of tolerance to extremely adverse conditions of climate and growing medium (soil, sand, and railings) combined into one plant as vetiver. All these special characteristics make vetiver a choice plant for phytoremediation of heavy metals and organic wastes.

Toxicol Sci. 2009 Oct 6;
Solari M, Paquin J, Ducharme P, Boily M

Atrazine and nitrogenous fertilizers are agrochemical contaminants frequently detected in water systems in North America. Several studies reported their ability to affect amphibian and mammalian development. Retinoids, supplied in the diet or synthesized by cells, are essential to embryogenesis. Disturbance of their homeostasis may lead to teratogenic effects. Retinoic acid (RA) is a major retinoid regulator of cell proliferation and differentiation. Previous studies reported alterations of retinoid stores in bullfrogs of Yamaska River subwatersheds (Québec, Canada), a region of intensive agricultural activities associated with Atrazine, nitrate and nitrite contaminants. These contaminants could affect RA metabolism and RA-mediated processes. Mouse P19 embryonic stem cells, which can differentiate to neurons in response to RA, were used to test this hypothesis. Cells were cultured in the absence or presence of contaminants during neuroinduction with RA, and assayed by flow cytometry for expression of SSEA1 (embryonic marker) and betaIII-tubulin (neuronal marker). Cell cultures were also analysed for RA metabolism by HPLC. Downregulation of SSEA1 paralleled betaIII-tubulin upregulation in a RA concentration-dependent manner. Atrazine, nitrate and nitrite did not affect differentiation at environmentally-encountered micromolar concentrations. However, low molar nitrite prevented RA-induced SSEA1 downregulation, and decreased betaIII-tubulin appearance. Decreased cell viability/proliferation accompanied these differentiation effects. P19 cells metabolized RA to polar retinoids. RA metabolism was not affected at any concentration of Atrazine, nitrate or nitrite. Environmentally-relevant levels of these contaminants thus had no gross effect on neurodifferentiation and RA catabolism of embryonic stem cells. P19 cell-based bioassays may provide valuable tools in monitoring developmental toxicity.

Ann Bot (Lond). 2009 Sep 29;
Ramel F, Sulmon C, Gouesbet G, Couée I

Background Soluble sugars are involved in responses to stress, and act as signalling molecules that activate specific or hormone cross-talk transduction pathways. Thus, exogenous sucrose treatment efficiently induces tolerance to the herbicide Atrazine in Arabidopsis thaliana plantlets, at least partially through large-scale modifications of expression of stress-related genes. Methods Availability of sugars in planta for stress responses is likely to depend on complex dynamics of soluble sugar accumulation, sucrose-starch partition and organ allocation. The question of potential relationships between endogenous sugar levels and stress responses to Atrazine treatment was investigated through analysis of natural genetic accessions of A. thaliana. Parallel quantitative and statistical analysis of biochemical parameters and of stress-sensitive physiological traits was carried out on a set of 11 accessions. Key Results Important natural variation was found between accessions of A. thaliana in pre-stress shoot endogenous sugar levels and responses of plantlets to subsequent Atrazine stress. Moreover, consistent trends and statistically significant correlations were detected between specific endogenous sugar parameters, such as the pre-stress end of day sucrose level in shoots, and physiological markers of Atrazine tolerance. Conclusions These significant relationships between endogenous carbohydrate metabolism and stress response therefore point to an important integration of carbon nutritional status and induction of stress tolerance in plants. The specific correlation between pre-stress sucrose level and greater Atrazine tolerance may reflect adaptive mechanisms that link sucrose accumulation, photosynthesis-related stress and sucrose induction of stress defences.

Curr Microbiol. 2009 Sep 16;
Hunter WJ, Shaner DL

Due to its high usage, mobility, and recalcitrant nature, Atrazine is a common groundwater contaminant. Moreover, groundwaters that are contaminated with Atrazine often contain nitrate as well. Nitrate interferes with the biological degradation of Atrazine and makes it more difficult to use in situ biological methods to remediate Atrazine contaminated groundwater. To solve this problem we used two reactors in sequence as models of in situ biobarriers; the first was a vegetable-oil-based denitrifying biobarrier and the second an aerobic reactor that oxygenated the denitrifying reactor's effluent. The reactors were inoculated with an Atrazine-degrading microbial consortium and supplied with water containing 5 mg l(-1) nitrate-N and 3 mg l(-1) Atrazine. Our hypothesis was that the denitrifying barrier would remove nitrate from the flowing water and that the downstream reaction would remove Atrazine. Our hypothesis proved correct; the two reactor system removed 99.9% of the Atrazine during the final 30 weeks of the study. The denitrifying barrier removed ~98% of the nitrate and ~30% of the Atrazine while the aerobic reactor removed ~70% of the initial Atrazine. The system continued to work when the amount of nitrate-N in the influent water was increased to 50 mg l(-1). A mercury poisoning study blocked the degradation of Atrazine indicating that biological processes were involved. An in situ denitrifying barrier coupled with an air injection system or other oxygenation process might be used to remove both nitrate and Atrazine from contaminated groundwater or to protect groundwater from an Atrazine spill.

Environ Sci Technol. 2009 Aug 15; 43(16): 6115
Hayes T

Chemosphere. 2009 Oct; 77(6): 785-90
Aguilera P, Briceño G, Candia M, Mora Mde L, Demanet R, Palma G

The application rate of liquid cow manure (LCM) in the field and the stabilization time of amended soils before application of pre-plant herbicides are factors that determine their efficiency. This study includes evaluation of residual Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) in soil and amended soils with equivalent rate of 100,000; 200,000; and 300,000 L ha(-1) of LCM and the effect of pre-incubation time of amended soils on Atrazine degradation. The study was carried out under controlled conditions using an Andisol with previous historical application of Atrazine. The respiratory activity and fluorescein diacetate (FDA) studies indicated that the time necessary for stabilization of amended soils is over 20-30 d. During the measurement of respiratory and FDA activity, no significant differences were observed when Atrazine was applied. The half-life of Atrazine ranged from 5 to 8d and the relative distribution of degradation products seem to be affected by the application of LCM. The pre-incubation time of amended soil and LCM dose would not affect Atrazine degradation rate, when the soil has a history of herbicide application. However, repeated applications of LCM in a long period of time could change the soil pH and increase the content of dissolved organic carbon (DOC) which could further contribute to a faster degradation of Atrazine. Both effects would reduce the effectiveness of Atrazine in weed control.

Bull Environ Contam Toxicol. 2009 Aug 27;
Mukherjee I

Pesticide contamination of soil and ground water at or near the agricultural fields is a major problem world wide. The ability of several amendments like rice straw, manure, saw dust and charcoal were used to stimulate the degradation of Atrazine in soil. Field soil fortified with pesticide at two concentration levels were amended separately with rice straw, farm yard manure, saw dust and charcoal at rates of 2.5% (w/w) and maintained at field capacity moisture regime and kept at ambient temperature 25 +/- 5 degrees C. The results indicate 89.5% degradation of Atrazine in farm yard manure during 60-day period followed by rice straw, saw dust charcoal and recording 87.2% and 83.8%, 67.7%, respectively, as compared to unamended treatment where 63.3% degradation was observed. The FYM was found to be most effective in soil and enhances the degradation as compared to the other amendments. Although addition of organic manures has been an integral part of sustainable agriculture practices; the present findings give a new dimension of it's utilization for removal of persistent pesticides.

Aquat Toxicol. 2009 Sep 14; 94(3): 211-8
Tryfonos M, Papaefthimiou C, Antonopoulou E, Theophilidis G

Organophosphates (OPs) can provoke toxicity by inhibiting acetylcholinesterase (AChE) in non-target organisms, like fish. In a previous pilot study, the anticholinesterase effects of paraoxon on the heart of Sparus aurata were examined [Tryfonos, M., Antonopoulou, E., Papaefthimiou, C., Chaleplis, G., Theophilidis, G., 2009. An in vitro assay for the assessment of the effects of an organophosphate, paraoxon, and a triazine, Atrazine, on the heart of the gilthead sea bream (Sparus aurata). Pest. Biochem. Physiol. 93, 40-46]. The objective of the present study was to investigate the effects of the five protoxicant OPs, azinphos-methyl (MeAZP), parathion-methyl (MePS), chlorpyriphos-methyl (MeCCP), methamidophos (MET) and diazinon (DZ), on the spontaneously beating auricle of S. aurata. The results showed that: (1) MeAZP and MET induced exclusively cholinergic effects on auricle contractility. These effects were expressed as a significant decrease in the force and frequency of contractions and were fully reversible (140%) after the application of the muscarinic cholinergic receptor antagonist, atropine (15 microM). MeAZP was found to be the most effective anticholinesterase compound, with an IC(50) of 2.19+/-1.05 microM (n=6), while MET was less effective, with an IC(50) of 72.3+/-1.2 microM (n=6). (2) DZ and MePS, although classified as OPs, induced non-cholinergic effects. These effects were observed as an irreversible decrease in force and frequency of the auricle in all the concentrations examined; the depression is retained even after application of 15 microM atropine. (3) MeCCP was halfway between a typical OP and an OP lacking anticholinesterase properties, since there was a partial recovery in the force, but no recovery in the frequency of the auricle contractions. (4) The toxicity order, based on the IC(50), was as follows: MeAZP, 2.19+/-1.05 microM>paraoxon, 3.2+/-1.5 microM"MET, 72.3+/-1.2 microM>MePS, 80.3+/-1.03 microM>MeCPP, 93.7+/-1.01 microM>DZ, 164+/-1.01 microM. (5) There was a good correlation (r=0.779, p=0.04, n=5) between IC(50) and the previously determined logP (octanol:water partition coefficient) values for MeAZP, paraoxon, MeCCP, MePS and DZ. The results indicated that the increase in lipophilicity of MePS, MeCCP and DZ is accompanied by a decrease in their acute cardiotoxic properties in vitro. The non-cholinergic effects of these relatively high lipophilic OPs, might be caused by their tendency to distribute preferentially in the lipid bilayer of cardiac cells, affecting the proper functioning of the ionic channels which regulate the force (Ca(2+) channels) and the frequency (K(+) channels) of the spontaneous auricle contractions.

Arch Environ Contam Toxicol. 2009 Aug 12;
Abarikwu SO, Adesiyan AC, Oyeloja TO, Oyeyemi MO, Farombi EO

To study the effects of Atrazine on reproductive functions and testicular and epididymal antioxidant defense, rats were exposed to 0, 120, or 200 mg/kg body weight Atrazine orally for 7 and 16 days. Animals exposed to the high-dose Atrazine had their body weights, feed intake, and reproductive organs weights significantly reduced, whereas testicular weights remain unaffected independent of the dose used. In comparison to control, glutathione (GSH) and glutathione-S-transferase (GST) activities were elevated in the high-dose group, whereas the activity of superoxide dismutase (SOD), catalase (CAT); ascorbate (AA), and malondialdehyde (MDA) levels and hydrogen peroxide production were unchanged in the testis during the 7-day-exposure protocol. When Atrazine treatment was increased to 16 days, GSH levels remained unchanged, but lipid peroxidation levels were significantly increased in both the testes and epididymides. This corresponded to the significant diminution in the activities of GST and SOD. CAT activities were unaffected in the testes and then dropped in the epididymides. gamma-Glutamyl transferase (gamma-GT) activities increased during both studies, whereas AA levels remained unaffected (p < 0.05). Atrazine exposure has a dose-dependent adverse effect on the testicular and epididymal sperm numbers, motility, viability, morphology, and daily sperm production. Although the testes of the Atrazine-treated animals appear normal, few tubules had mild degeneration with the presence of defoliated cells. Likewise, no perceptible morphological changes were observed in the epididymis. The results suggest that Atrazine impairs reproductive function and elicits a depletion of the antioxidant defense system in the testis and epididymis, indicating the induction of oxidative stress.

J Hazard Mater. 2009 Dec 30; 172(2-3): 675-84
Chen C, Yang S, Guo Y, Sun C, Gu C, Xu B

The ultraviolet (UV) photolysis of Atrazine in aqueous solution was investigated at wavelength of 254 nm in this study. This paper was mainly focused on the identification of Atrazine degradation intermediates by HPLC-MS/MS and its degradation mechanisms. The photodegradation products included the following seven classes: dechloro-hydroxylated products, chloro-dealkylated products, dechloro-dealkylated products, alkylic-oxidated products, delamination-hydroxylated products, olefinic products, and dechloro-hydrogenated products which were never reported in direct photolytic process, 4-isopropylamino-6-ethylamino-s-triazine (IEST), 4,6-dihydroxy-s-triazine (OOST). The main degradation products were 2-hydroxy-4-acetamido-6-ethylamino-s-triazine (OIET), 2-chloro-4-isopropyl-amino-6-methylamino-s-triazine (CIMT), 2-chloro-4,6-divinylamino-s-triazine (CVVT), 2-chloro-4-ethylamino-6-amino-s-triazine(CEAT), 2-methoxy-4-isopropyl-amino-6-methylamino-s-triazine (OIMT), 2-hydroxy-4-acetamindo-6-ethylamino-s-triazine (ODET), etc. Finally, the possible degradation mechanism was also proposed here.

Chemosphere. 2009 Oct; 77(3): 404-12
Dong X, Zhu L, Wang J, Wang J, Xie H, Hou X, Jia W

In this study, the effects of Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) in males and females of adult zebrafish (Danio rerio) were studied. The liver microsomal cytochrome P450 content, NADPH-P450 reductase, aminopyrine N-demethylase (APND), and erythromycin N-demethylase (ERND) activity were measured. Zebrafish were exposed to control and 3 treatments (0.01, 0.1, and 1 mg L(-1)) of Atrazine for 5, 10, 15, 20, and 25 days. The results indicated that, within the range of test Atrazine concentrations, either P450 content or P450 isozyme activities could be induced by Atrazine. Compared to controls, P450 content was significantly increased at all Atrazine concentrations at days 10, 15, and 20; thereafter, at day 25, all concentrations decreased to approximately the control levels, both in males and females. In addition, the strongest induction of P450 content was observed on day 15 in males and day 10 in females at treatment concentrations of 1 mg L(-1). NADPH-P450 reductase activities showed mild increase in males; however, the females exhibited significant induction on days 15, 20, and 25; especially, at concentrations of 0.01 mg L(-1), the induction level was consistently increased during the experiment. The inducements of APND and ERND in males were mainly observed on the days 5, 10, and 15, which showed less distinct induction, while significant induction was observed in cases of treatments during all days in females. In conclusion, Atrazine induces P450 enzymes in zebrafish, and the effects may function as significant toxicity mechanisms in zebrafish. Additionally, it also confirms the importance of using a combined multi-time and multi-index diagnostic method to enhance the sensitivity and effectiveness of the indices adopted.

Chemosphere. 2009 Oct; 77(4): 574-81
Spokas KA, Koskinen WC, Baker JM, Reicosky DC

A potential abatement to increasing levels of carbon dioxide (CO(2)) in the atmosphere is the use of pyrolysis to convert vegetative biomass into a more stable form of carbon (biochar) that could then be applied to the soil. However, the impacts of pyrolysis biochar on the soil system need to be assessed before initiating large scale biochar applications to agricultural fields. We compared CO(2) respiration, nitrous oxide (N(2)O) production, methane (CH(4)) oxidation and herbicide retention and transformation through laboratory incubations at field capacity in a Minnesota soil (Waukegan silt loam) with and without added biochar. CO(2) originating from the biochar needs to be subtracted from the soil-biochar combination in order to elucidate the impact of biochar on soil respiration. After this correction, biochar amendments reduced CO(2) production for all amendment levels tested (2, 5, 10, 20, 40 and 60% w/w; corresponding to 24-720 tha(-1) field application rates). In addition, biochar additions suppressed N(2)O production at all levels. However, these reductions were only significant at biochar amendment levels >20% w/w. Biochar additions also significantly suppressed ambient CH(4) oxidation at all levels compared to unamended soil. The addition of biochar (5% w/w) to soil increased the sorption of Atrazine and acetochlor compared to non-amended soils, resulting in decreased dissipation rates of these herbicides. The recalcitrance of the biochar suggests that it could be a viable carbon sequestration strategy, and might provide substantial net greenhouse gas benefits if the reductions in N(2)O production are lasting.

J Environ Qual. 2009 Sep-Oct; 38(5): 1861-9
Shaner DL, Wiles L, Hansen N

Glyphosate-resistant (GR) corn may be a major component of new cropping systems to optimize the use of limited irrigation water supply while sustaining production. Because Atrazine is an important tool for residual weed control in GR corn, we examined Atrazine binding to soil, dissipation, movement, and early season weed control in limited and full irrigation cropping systems. These systems included continuous corn under conventional tillage and full irrigation (CCC-FI) and under no-tillage and deficit irrigation (CCC-DI), a sunflower-wheat-corn rotation under no-tillage and deficit irrigation (SWC-DI), and a wheat-fallow-wheat-corn rotation under no tillage and natural precipitation (WFWC-NP). Crop rotation and herbicide use history influenced Atrazine behavior more than amount or type of irrigation. Atrazine dissipated more rapidly in the top 30 cm of soil in the CCC-FI and CCC-DI plots (half-life [T(1/2)] = 3-12 d), which had received previous applications of the herbicide, compared with the SWC-DI and WFWC-NP plots, which had no history of Atrazine use (T(1/2) = 15-22 d). Laboratory assays indicated that the different rates of degradation were at least partly due to differences in microbial degradation in the soil. Atrazine moved the most in the top 30 cm in the SWC-DI and WFWC-NP plots. This greater movement is probably due to the slower rate of Atrazine degradation. Studies of the behavior of pre-emergence herbicides in new limited irrigation cropping systems must consider all characteristics of the systems, not just amount and timing of irrigation.

J Environ Qual. 2009 Sep-Oct; 38(5): 1803-11
Waria M, Comfort SD, Onanong S, Satapanajaru T, Boparai H, Harris C, Snow DD, Cassada DA

A former agrichemical dealership in western Nebraska was suspected of having contaminated soil. Our objective was to characterize and remediate the contaminated site by a combined chemical-biological approach. This was accomplished by creating contour maps of the on-site contamination, placing the top 60 cm of contaminated soil in windrows and mixing with a mechanical high-speed mixer. Homogenized soil containing both Atrazine [6-chloro-N-ethyl-N'-isopropyl-1,3,5-triazine-2,4-diamine] and cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} was then used in laboratory investigations to determine optimum treatments for pesticide destruction. Iron suspension experiments verified that zerovalent iron (Fe(0)) plus ferrous sulfate (FeSO(4).7H(2)O) removed more than 90% of both Atrazine and cyanazine within 14 d. Liquid chromatography/mass spectrometry (LC/MS) analysis of the Atrazine solution after treating with Fe(0) and ferrous sulfate identified several degradation products commonly associated with biodegradation (i.e., deethlyAtrazine (DEA), deisopropylAtrazine (DIA), hydroxyAtrazine (HA), and ammelines). Biological treatment evaluated emulsified soybean [Glycine max (L.) Merr.] oil (EOS) as a carbon source to stimulate biodegradation in static soil microcosms. Combining emulsified soybean oil with the chemical amendments resulted in higher destruction efficiencies (80-85%) and reduced the percentage of FeSO(4) needed. This chemical-biological treatment (Fe(0) + FeSO(4) + EOS, EOS Remediation, Raleigh, NC) was then applied with water to 275 m(3) of contaminated soil in the field. Windrows were tightly covered with clear plastic to increase soil temperature and maintain soil water content. Temporal sampling (0-342 d) revealed Atrazine and cyanazine concentrations decreased by 79 to 91%. These results provide evidence that a combined chemical-biological approach can be used for on-site, field-scale treatment of pesticide-contaminated soil.

Biodegradation. 2009 Jul 15;
Yang C, Li Y, Zhang K, Wang X, Ma C, Tang H, Xu P

A simple consortium consisted of two members of Klebsiella sp. A1 and Comamonas sp. A2 was isolated from the sewage of a pesticide mill in China. One member of Klebsiella sp. A1 is a novel strain that could use Atrazine as the sole carbon and nitrogen source. The consortium showed high Atrazine-mineralizing efficiency and about 83.3% of 5 g l(-1) Atrazine could be mineralized after 24 h degradation. Contrary to many other reported microorganisms, the consortium was insensitive to some nitrogenous fertilizers commonly used, not only in presence of 200 mg l(-1) Atrazine but also in 5 g l(-1) Atrazine mediums. After 24 h incubation, 200 mg l(-1) Atrazine was completely mineralized despite of the presence of urea, (NH(4))(2)CO(3) and (NH(4))(2)HPO(4) in the medium. Very minor influence was observed when NH(4)Cl was added as additional nitrogen source. Advantages of the simple consortium, high mineralizing efficiency and insensitivity to most of exogenous nitrogen sources, all suggested application potential of the consortium for the bioremediation of Atrazine-contaminated soils and waters.

Chemosphere. 2009 Oct; 77(4): 590-6
Satsuma K

A microbial community, designated as AN4, capable of mineralizing the herbicide Atrazine was isolated from a model river ecosystem (microcosm). The profile of degradation of Atrazine by the AN4 community seemed to well reflect what occurred in the microcosm: rapid degradation of Atrazine and transient accumulation of cyanuric acid, followed by relatively slow mineralization. The community comprised multiple phylogenetically distinct microbial strains, and the microbes were suspended and probably aggregated in the water phase of the microcosm. Denaturing gradient gel electrophoresis (DGGE) revealed that multiple bacterial strains exist in the AN4 community, and we successfully isolated two strains, which belonged to the genera Nocardioides and Pedomicrobium. Nocardioides sp. strain AN4-4 degraded Atrazine to cyanuric acid and harbored the trzN and atzC genes encoding the s-triazine-degrading enzymes. This strain also degraded other chloro-substituted s-triazines like simazine and propazine, but it showed little degradability for simetryn (a methylthio-substituted s-triazine). Additionally, strain AN4-4 could grow on basal salt agar containing ethylamine or isopropylamine as the only carbon and nitrogen sources. Another strain, Pedomicrobium sp. strain AN4-9 could mineralize cyanuric acid alone. Therefore, we found that the coexistence of these two community members functionally serves to completely biodegrade Atrazine.

Appl Environ Microbiol. 2009 Sep; 75(17): 5481-8
Liu X, Parales RE

Pseudomonas sp. strain ADP utilizes the human-made s-triazine herbicide Atrazine as the sole nitrogen source. The results reported here demonstrate that Atrazine and the Atrazine degradation intermediates N-isopropylammelide and cyanuric acid are chemoattractants for strain ADP. In addition, the nonmetabolized s-triazine ametryn was also an attractant. The chemotactic response to these s-triazines was not specifically induced during growth with Atrazine, and Atrazine metabolism was not required for the chemotactic response. A cured variant of strain ADP (ADP M13-2) was attracted to s-triazines, indicating that the Atrazine catabolic plasmid pADP-1 is not necessary for the chemotactic response and that Atrazine degradation and chemotaxis are not genetically linked. These results indicate that Atrazine and related s-triazines are detected by one or more chromosomally encoded chemoreceptors in Pseudomonas sp. strain ADP. We demonstrated that Escherichia coli is attracted to the s-triazine compounds N-isopropylammelide and cyanuric acid, and an E. coli mutant lacking Tap (the pyrimidine chemoreceptor) was unable to respond to s-triazines. These data indicate that pyrimidines and triazines are detected by the same chemoreceptor (Tap) in E. coli. We showed that Pseudomonas sp. strain ADP is attracted to pyrimidines, which are the naturally occurring structures closest to triazines, and propose that chemotaxis toward s-triazines may be due to fortuitous recognition by a pyrimidine chemoreceptor in Pseudomonas sp. strain ADP. In competition assays, the presence of Atrazine inhibited chemotaxis of Pseudomonas sp. strain ADP to cytosine, and cytosine inhibited chemotaxis to Atrazine, suggesting that pyrimidines and s-triazines are detected by the same chemoreceptor.

J Phys Chem A. 2009 Jul 30; 113(30): 8596-606
da Silva G, Bozzelli JW, Asatryan R

Reaction with the hydroxyl radical (HO(*)) is the primary removal mechanism for organic compounds in the atmosphere, and an important process in combustion. Molecules with unsaturated carbon sites are thought to react with HO(*) via a rapid addition mechanism, with little or no barrier; this results in short lifetimes relative to the saturated alkanes, which undergo slower abstraction reactions. Computational chemistry and reaction rate theory are used in this study to investigate the s-triazine + HO(*) reaction. We report that HO(*) addition at a carbon ring site proceeds with the largest known barrier for addition to an unsaturated carbon (9.8 kcal mol(-1) at the G3X level of theory). Abstraction of a hydrogen atom in s-triazine by HO(*), forming the s-triazinyl radical + H(2)O, proceeds with a barrier of only 3.3 kcal mol(-1), and this process dominates over HO(*) addition. Our results are in contrast to those for the analogous reactions in benzene, where the abstraction reaction to phenyl + H(2)O is slower than the HO(*) addition, which forms a radical adduct that can further react with O(2) or dissociate to phenol + H(*). The lifetime of s-triazine toward the hydroxyl radical in the troposphere is estimated at 6.4 years, potentially making it a long-lived pollutant. The aromatic s-triazine (1,3,5-triazine) molecule is a structural feature in herbicides such as Atrazine and is a decomposition product of the common energetic material cyclotrimethylenetrinitramine (RDX). While the abstraction reaction dominates for the parent s-triazine, the addition mechanism may be of importance in the atmospheric degradation of substituted triazines, like Atrazine, where ring H atoms are not available for abstraction. The high-barrier addition mechanism forms an activated hydroxy-triazinyl adduct which predominantly dissociates to 2-hydroxy-1,3,5-triazine (OST) + H(*). This OST species is a known intermediate of RDX decomposition. Results are also presented for isomerization of the less-stable 1,3,5-triazine-N-oxide OST species (which may form via unimolecular pathways in the liquid-phase decomposition of RDX) to 2-hydroxy-1,3,5-triazine. A reaction mechanism is proposed for further oxidation of the s-triazinyl radical, where an OST isomer is also a potential product.