Combined metabolic activity within an atrazine-mineralizing community enriched from agrochemical factory soil

The main objective of this work was to characterize an atrazine-mineralizing community originating from agrochemical factory soil, especially to elucidate the catabolic pathway and individual metabolic and genetic potentials of culturable members. A stable four-member bacterial community, characterized by colony morphology and 16S rDNA sequencing, was rapidly able to mineralize atrazine to CO₂ and NH₃. Two primary organisms were identified as Arthrobacter species (ATZ1 and ATZ2) and two secondary organisms (CA1 and CA2) belonged to the genera Ochrobactrum and Pseudomonas, respectively. PCR assessment of atrazine-degrading genetic potential of the community, revealed the presence of trzN, trzD, atzB and atzC genes. Isolates ATZ1 and ATZ2 were capable of dechlorinating atrazine to hydroxyatrazine and contained the trzN gene. ATZ2 further degraded hydroxyatrazine to cyanuric acid and contained atzB and atzC genes whereas ATZ1 contained atzC but not atzB. Isolates CA1 and CA2 grew on cyanuric acid and contained the trzD gene. Complete atrazine degradation was a result of the combined metabolic attack on the atrazine molecule, and complex interactions may exist between the community members sharing carbon and nitrogen from atrazine mineralization.Scientific relevance: Despite numerous reports on atrazine degradation by pure bacterial cultures, the pathways and the atrazine-degrading gene combinations harboured by bacterial communities are only poorly described. In this work, we characterized a four-member atrazine-mineralizing community enriched from an agrochemical factory soil, which was capable of rapidly metabolizing atrazine to CO₂. This study will contribute towards better understanding of the genetic potential and metabolic activities of atrazine-degrading communities, which are generally considered to be responsible for atrazine mineralization in the natural environment.     

Contribution of ethylamine degrading bacteria to atrazine degradation in soils

Bacterial communities that cooperatively degrade atrazine commonly consist of diverse species in which the genes for atrazine dechlorination and dealkylation are variously distributed among different species. Normally, the first step in degradation of atrazine involves dechlorination mediated by atzA, followed by stepwise dealkylation to yield either N-ethylammelide or N-isopropylammelide. As the liberated alkylamine moieties are constituents of many organic molecules other than atrazine, it is possible that a large number of alkylamine-degrading bacteria other than those previously described might contribute to this key step in atrazine degradation. To examine this hypothesis, we isolated 82 bacterial strains from soil by plating soil water extracts on agar media with ethylamine as a sole carbon source. Among the relatively large number of isolates, only 3 were able to degrade N-ethylammelide, and in each case were shown to carry the atzB gene and atzC genes. The isolates, identified as Rhizobium leguminosarum, Flavobacterium sp., and Arthrobacter sp., were all readily substituted into an atrazine-degrading consortium to carry out N-ethylammelide degradation. The distribution of these genes among many different species in the soil microbial population suggests that these genes are highly mobile and over time may lead to generation of various atrazine-degrading consortia.     

Cloning, characterization, and expression of a gene region from Pseudomonas sp. strain ADP involved in the dechlorination of atrazine.

We previously identified a Pseudomonas sp. strain, ADP, which rapidly metabolized atrazine in liquid culture, agar plates, and soils (R. T. Mandelbaum, D. L. Allan, L. P. Wackett, Appl. Environ. Microbiol. 61:1451-1457, 1995). In this study, we report the cloning and partial characterization of a gene region from Pseudomonas sp. strain ADP that encodes atrazine degradation activity. A 22-kb EcoRI genomic DNA fragment, designated pMD1, was shown to encode atrazine dechlorination activity in Escherichia coli DH5 alpha. Atrazine degradation was demonstrated by a zone-clearing assay on agar medium containing crystalline atrazine and by chromatographic methods. A gene conferring the atrazine-clearing phenotype was subsequently subcloned as a 1.9-kb AvaI fragment in pACYC184, designated pMD4, and was expressed in E. coli. This result and random Tn5 mutagenesis established that the 1.9-kb AvaI fragment was essential for atrazine dechlorination. High-pressure liquid and thin-layer chromatographic analyses were used to rigorously establish that E. coli containing pMD4 degraded atrazine and accumulated hydroxyatrazine. Hydroxyatrazine was detected only transiently in E. coli containing pMD1. This is consistent with the idea that hydroxyatrazine is the first metabolite in atrazine degradation by Pseudomonas sp. strain ADP. A 0.6-kb ApaI-PstI fragment from pMD4, containing the putative atrazine chlorohydrolase gene, hybridized to DNA from atrazine-degrading bacteria isolated in Switzerland and Louisiana.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dechlorination of Atrazine by a Rhizobium sp. Isolate

A Rhizobium sp. strain, named PATR, was isolated from an agricultural soil and found to actively degrade the herbicide atrazine. Incubation of PATR in a basal liquid medium containing 30 mg of atrazine liter(sup-1) resulted in the rapid consumption of the herbicide and the accumulation of hydroxyatrazine as the only metabolite detected after 8 days of culture. Experiments performed with ring-labeled [(sup14)C]atrazine indicated no mineralization. The enzyme responsible for the hydroxylation of atrazine was partially purified and found to consist of four 50-kDa subunits. Its synthesis in PATR was constitutive. This new atrazine hydrolase demonstrated 92% sequence identity through a 24-amino-acid fragment with atrazine chlorohydrolase AtzA produced by Pseudomonas sp. strain ADP.     

Molecular Basis of a Bacterial Consortium: Interspecies Catabolism of Atrazine

Pseudomonas sp. strain ADP contains the genes, atzA, -B, and -C, that encode three enzymes which metabolize atrazine to cyanuric acid. Atrazine-catabolizing pure cultures isolated from around the world contain genes homologous to atzA, -B, and -C. The present study was conducted to determine whether the same genes are present in an atrazine-catabolizing bacterial consortium and how the genes and metabolism are subdivided among member species. The consortium contained four or more bacterial species, but two members, Clavibacter michiganese ATZ1 and Pseudomonas sp. strain CN1, collectively mineralized atrazine. C. michiganese ATZ1 released chloride from atrazine, produced hydroxyatrazine, and contained a homolog to the atzA gene that encoded atrazine chlorohydrolase. C. michiganese ATZ1 stoichiometrically metabolized hydroxyatrazine to N-ethylammelide and contained genes homologous to atzB and atzC, suggesting that either a functional AtzB or -C catalyzed N-isopropylamine release from hydroxyatrazine. C. michiganese ATZ1 grew on isopropylamine as its sole carbon and nitrogen source, explaining the ability of the consortium to use atrazine as the sole carbon and nitrogen source. A second consortium member, Pseudomonas sp. strain CN1, metabolized the N-ethylammelide produced by C. michiganese ATZ1 to transiently form cyanuric acid, a reaction catalyzed by AtzC. A gene homologous to the atzC gene of Pseudomonas sp. strain ADP was present, as demonstrated by Southern hybridization and PCR. Pseudomonas sp. strain CN1, but not C. michiganese, metabolized cyanuric acid. The consortium metabolized atrazine faster than did C. michiganese individually. Additionally, the consortium metabolized a much broader set of triazine ring compounds than did previously described pure cultures in which the atzABC genes had been identified. These data begin to elucidate the genetic and metabolic bases of catabolism by multimember consortia.     

阿特拉津降解菌株的分离、鉴定和工业废水生物处理试验

用液体无机盐培养基富集培养法和无机盐平板直接分离法, 从生产阿特拉津的农药厂的废水和污泥混合物中分离到13个能以阿特拉津为唯一氮源生长的细菌菌株。通过16S rRNA基因序列分析, 11个菌株被鉴定为Arthrobacter spp., 2个菌株被鉴定为Pseudomonas spp.。对阿特拉津降解活力最高的Arthrobacter sp. AD30和Pseudomonas sp. AD39的降解基因组成和降解特性进行了详细研究。降解基因的PCR扩增表明, AD30和AD39都含有trzN-atzBC基因, 能将有毒的阿特拉津降解成无毒的氰尿酸。降解实验表明, 向阿特拉津浓度为200 mg/L的无机盐培养基中分别接种等量的AD30、AD39和这两个菌株的混合菌液, 30°C振荡培养48 h以后, 阿特拉津去除率分别为92.5%、97.9%和99.6%, 表明混合菌的降解效果好于单菌。用AD30和AD39的混合菌液接种阿特拉津浓度为176 mg/L的工业废水, 30°C振荡培养72 h以后, 99.1%的阿特拉津被去除, 表明混合菌株在阿特拉津工业废水的生物处理中有很好的应用潜力。     

Metabolism of Atrazine in Liquid Cultures and Soil Microcosms by Nocardioides Strains Isolated from a Contaminated Nigerian Agricultural Soil

Atrazine-degrading microorganisms designated EAA-3 and EAA-4, belonging to the genus Nocardioides, were obtained from an agricultural soil in Nigeria. The degradation kinetics of the two strains revealed total disappearance of 25 mg l^?1 of atrazine in less than 72 h of incubation at the rate of 0.42 mg l^?1 h^?1 and 0.35 mg l^?1 h^?1, respectively. Screening for atrazine catabolic genes in these organisms revealed the presence of trzN, atzB, and atzC. Other genes, specifically atzA, atzD, and trzD, were not detected. Potential intermediates of atrazine catabolic route such as hydroxyatrazine, desethylatrazine, and desisopropylatrazine were utilized as sources of carbon and energy, while desisopropyl desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine were attacked but in the presence of glucose. A soil microcosm study showed that degradation was faster in microcosms contaminated with 13 mg of atrazine per g^?1 of soil compared with 480 mg g^?1 of soil. In the former, degradation was 10% higher in the inoculated soil than the non-inoculated control (natural attenuation) over the 28-day study period. Corresponding value obtained for the latter was nearly 70% higher. This study has demonstrated that the bacterial strains isolated enhanced atrazine degradation and the catabolic activities of these strains were not affected with increasing soil atrazine concentration.     

Accelerated biodegradation of atrazine by a microbial consortium is possible in culture and soil

A mixed enrichment culture of microorganisms capable of accelerated mineralization of atrazine was isolated from soil treated with successive applications of the herbicide. Liquid cultures of this consortium, in the presence of simple carbon sources, mineralized 96% of the applied atrazine (0.56 mM) within 7 days. Atrazine mineralization in culture is initiated with the formation of the metabolite hydroxyatrazine. In soil treated with atrazine at a concentration of 0.14 mM (concentration is based on total soil mass), and then inoculated with the microbial consortium, the parent compound was completely transformed in 25 days. After 30 days of incubation, 60% of the applied atrazine was accounted for as¹⁴CO₂. As was found with the liquid cultures, hydroxyatrazine was the major metabolite. After 145 days, soil extractable hydroxyatrazine declined to zero and 86% of the applied atrazine was accounted for as¹⁴CO₂. No metabolites, other than hydroxyatrazine, were recovered from either the liquid culture or soil inoculated with the consortium. The use of the mixed microbial culture enhanced mineralization more than 20 fold as compared to uninoculated soil.     

Isolation and characterization of an atrazine-degrading Rhodococcus sp. strain MB-P1 from contaminated soil

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.     

Isolation and Characterization of a Pseudomonas sp. That Mineralizes the s-Triazine Herbicide Atrazine

A bacterium that was capable of metabolizing atrazine at very high concentrations (>1,000 ppm) was isolated from a herbicide spill site. The organism was differentiated by observing clearing zones on indicator agar plates containing 1,000 ppm atrazine. Detailed taxonomic studies identified the organism as a Pseudomonas sp., designated ADP, that was dissimilar to currently known species. Pseudomonas sp. strain ADP metabolized atrazine as its sole nitrogen source. Nongrowing suspended cells also metabolized atrazine rapidly; for example, 9 x 10(sup9) cells per ml degraded 100 ppm of atrazine in 90 min. Atrazine was metabolized to hydroxyatrazine, polar metabolites, and carbon dioxide. When uniformly ring-labeled [(sup14)C]atrazine was used, 80% of the radioactivity was liberated as (sup14)CO(inf2). These data indicated the triazine ring was completely mineralized. The isolation and characterization of Pseudomonas sp. strain ADP may contribute to efforts on atrazine bioremediation, particularly in environments containing very high pesticide levels.     

mRNA differential display in a microbial enrichment culture: simultaneous identification of three cyclohexanone monooxygenases from three species

mRNA differential display has been used to identify cyclohexanone oxidation genes in a mixed microbial community derived from a wastewater bioreactor. Thirteen DNA fragments randomly amplified from the total RNA of an enrichment subculture exposed to cyclohexanone corresponded to genes predicted to be involved in the degradation of cyclohexanone. Nine of these DNA fragments are part of genes encoding three distinct Baeyer-Villiger cyclohexanone monooxygenases from three different bacterial species present in the enrichment culture. In Arthrobacter sp. strain BP2 and Rhodococcus sp. strain Phi2, the monooxygenase is part of a gene cluster that includes all the genes required for the degradation of cyclohexanone, while in Rhodococcus sp. strain Phi1 the genes surrounding the monooxygenase are not predicted to be involved in this degradation pathway but rather seem to belong to a biosynthetic pathway. Furthermore, in the case of Arthrobacter strain BP2, three other genes flanking the monooxygenase were identified by differential display, demonstrating that the repeated sampling of bacterial operons shown earlier for a pure culture (D. M. Walters, R. Russ, H. Knackmuss, and P. E. Rouvière, Gene 273:305-315, 2001) is also possible for microbial communities. The activity of the three cyclohexanone monooxygenases was confirmed and characterized following their expression in Escherichia coli.     

Fitness drift of an atrazine-degrading population under atrazine selection pressure

Pseudomonas sp. ADP harbouring the atrazine catabolic plasmid ADP1 was subcultured in liquid medium containing atrazine as sole source of nitrogen. After approximately 320 generations, a new population evolved which replaced the initial population. This newly evolved population grew faster and degraded atrazine more rapidly than the initial population. Plasmid profiles and Southern blot analyses revealed that the evolved strain, unlike the ancestral strain, presented a tandem duplication of the atzB gene encoding the second enzyme of the atrazine catabolic pathway responsible for the transformation of hydroxyatrazine to N-isopropylammelide. This duplication resulted from a homologous recombination that occurred between two direct repeats of 6.2 kb flanking the atzB gene and constituted by the insertion sequences IS 1071 , IS Pps1 and a pdhL homologous sequence. This study highlights the IS-mediated plasticity of atrazine-degrading potential and demonstrates that insertion sequences not only help to disperse the atrazine-degrading gene but also improve the fitness of the atrazine-degrading population.     

Biodegradation of atrazine in transgenic plants expressing a modified bacterial atrazine chlorohydrolase (atzA) gene

Atrazine is one of the most widely used herbicides in the USA. Atrazine chlorohydrolase (AtzA), the first enzyme in a six-step pathway leading to the mineralization of atrazine in Gram-negative soil bacteria, catalyses the hydrolytic dechlorination and detoxification of atrazine to hydroxyatrazine. In this study, we investigated the potential use of transgenic plants expressing atzA to take up, dechlorinate and detoxify atrazine. Alfalfa, Arabidopsis thaliana and tobacco were transformed with a modified bacterial atzA gene, p-atzA, under the control of the cassava vein mosaic virus promoter. All transgenic plant species actively expressed p-atzA and grew over a wide range of atrazine concentrations. Thin layer chromatography analyses indicated that in planta expression of p-atzA resulted in the production of hydroxyatrazine. Hydroponically grown transgenic tobacco and alfalfa dechlorinated atrazine to hydroxyatrazine in leaves, stems and roots. Moreover, p-atzA was found to be useful as a conditional-positive selection system to isolate alfalfa and Arabidopsis transformants following Agrobacterium-mediated transformation. Our work suggests that the in planta expression of p-atzA may be useful for the development of plants for the phytoremediation of atrazine-contaminated soils and soil water, and as a marker gene to select for the integration of exogenous DNA into the plant genome.     

Phylogenetic analysis of symbiotic genes of nodule bacteria in the plants of the genus Lathyrus (L.) (Fabaceae)

The comparative analysis of the symbiotic genes nifD, nifH, nodA of wild-growing Lathyrus L. species (Fabaceae) connected by genes sequences of 16S aRNA to Rhizobium leguminosarum bv. viceae, Rhizobium tropici, Agrobacterium sp., and Phyllobacterium sp. was carried out. It was demonstrated that all tested genes of strains taken for analysis had high degree of homology with analogous genes of Rhizobium leguminosarum bv. viceae. It was suggested that symbiotic genes were introduced into Rhizobium tropici, Agrobacterium sp., and Phyllobacterium sp. strains by means of horizontal gene transfer over from Rhizobium leguminosarum bv. viceae strain. The recombinant strains were formed, capable to nodulate Lathyrus L. species that earlier was not considered characteristic for these plants.     

Synergistic degradation of linuron by a bacterial consortium and isolation of a single linuron-degrading variovorax strain

The bacterial community composition of a linuron-degrading enrichment culture and the role of the individual strains in linuron degradation have been determined by a combination of methods, such as denaturing gradient gel electrophoresis of the total 16S rRNA gene pool, isolation and identification of strains, and biodegradation assays. Three strains, Variovorax sp. strain WDL1, Delftia acidovorans WDL34, and Pseudomonas sp. strain WDL5, were isolated directly from the linuron-degrading culture. In addition, subculture of this enrichment culture on potential intermediates in the degradation pathway of linuron (i.e., N,O-dimethylhydroxylamine and 3-chloroaniline) resulted in the isolation of, respectively, Hyphomicrobium sulfonivorans WDL6 and Comamonas testosteroni WDL7. Of these five strains, only Variovorax sp. strain WDL1 was able to use linuron as the sole source of C, N, and energy. WDL1 first converted linuron to 3,4-dichloroaniline (3,4-DCA), which transiently accumulated in the medium but was subsequently degraded. To the best of our knowledge, this is the first report of a strain that degrades linuron further than the aromatic intermediates. Interestingly, the rate of linuron degradation by strain WDL1 was lower than that for the consortium, but was clearly increased when WDL1 was coinoculated with each of the other four strains. D. acidovorans WDL34 and C. testosteroni WDL7 were found to be responsible for degradation of the intermediate 3,4-DCA, and H. sulfonivorans WDL6 was the only strain able to degrade N,O-dimethylhydroxylamine. The role of Pseudomonas sp. strain WDL5 needs to be further elucidated. The degradation of linuron can thus be performed by a single isolate, Variovorax sp. strain WDL1, but is stimulated by a synergistic interaction with the other strains isolated from the same linuron-degrading culture.     

一株高效广谱莠去津降解菌SB5的生长和降解特性

本研究采用富集培养技术自莠去津污染的活性污泥中分离筛选到一株具有降解三嗪类除草剂功能的菌株SB5,经形态学和16S rRNA基因分析将其初步鉴定为类节杆菌属细菌.其具有已知莠去津降解相关基因trzN、atzB及atzC.在培养基中添加葡萄糖、蔗糖、柠檬酸钠、酵母浸粉和蛋白胨可显著提高菌株SB5的生物量和对莠去津的降解效...     

Characterization of S-triazine herbicide metabolism by a Nocardioides sp. isolated from agricultural soils

Atrazine, a herbicide widely used in corn production, is a frequently detected groundwater contaminant. Nine gram-positive bacterial strains able to use this herbicide as a sole source of nitrogen were isolated from four farms in central Canada. The strains were divided into two groups based on repetitive extragenic palindromic (rep)-PCR genomic fingerprinting with ERIC and BOXA1R primers. Based on 16S ribosomal DNA sequence analysis, both groups were identified as Nocardioides sp. strains. None of the isolates mineralized [ring-U-(14)C]atrazine. There was no hybridization to genomic DNA from these strains using atzABC cloned from Pseudomonas sp. strain ADP or trzA cloned from Rhodococcus corallinus. S-Triazine degradation was studied in detail in Nocardioides sp. strain C190. Oxygen was not required for atrazine degradation by whole cells or cell extracts. Based on high-pressure liquid chromatography and mass spectrometric analyses of products formed from atrazine in incubations of whole cells with H(2)(18)O, sequential hydrolytic reactions converted atrazine to hydroxyatrazine and then to the end product N-ethylammelide. Isopropylamine, the putative product of the second hydrolytic reaction, supported growth as the sole carbon and nitrogen source. The triazine hydrolase from strain C190 was isolated and purified and found to have a K(m) for atrazine of 25 microM and a V(max) of 31 micromol/min/mg of protein. The subunit molecular mass of the protein was 52 kDa. Atrazine hydrolysis was not inhibited by 500 microM EDTA but was inhibited by 100 microM Mg, Cu, Co, or Zn. Whole cells and purified triazine hydrolase converted a range of chlorine or methylthio-substituted herbicides to the corresponding hydroxy derivatives. In summary, an atrazine-metabolizing Nocardioides sp. widely distributed in agricultural soils degrades a range of s-triazine herbicides by means of a novel s-triazine hydrolase.     

mRNA Differential Display in a Microbial Enrichment Culture: Simultaneous Identification of Three Cyclohexanone Monooxygenases from Three Species

mRNA differential display has been used to identify cyclohexanone oxidation genes in a mixed microbial community derived from a wastewater bioreactor. Thirteen DNA fragments randomly amplified from the total RNA of an enrichment subculture exposed to cyclohexanone corresponded to genes predicted to be involved in the degradation of cyclohexanone. Nine of these DNA fragments are part of genes encoding three distinct Baeyer-Villiger cyclohexanone monooxygenases from three different bacterial species present in the enrichment culture. In Arthrobacter sp. strain BP2 and Rhodococcus sp. strain Phi2, the monooxygenase is part of a gene cluster that includes all the genes required for the degradation of cyclohexanone, while in Rhodococcus sp. strain Phi1 the genes surrounding the monooxygenase are not predicted to be involved in this degradation pathway but rather seem to belong to a biosynthetic pathway. Furthermore, in the case of Arthrobacter strain BP2, three other genes flanking the monooxygenase were identified by differential display, demonstrating that the repeated sampling of bacterial operons shown earlier for a pure culture (D. M. Walters, R. Russ, H. Knackmuss, and P. E. Rouvière, Gene 273:305-315, 2001) is also possible for microbial communities. The activity of the three cyclohexanone monooxygenases was confirmed and characterized following their expression in Escherichia coli.     

Biodegradation and bioremediation of endosulfan contaminated soil

Among the three mixed bacterial culture AE, BE, and CE, developed by enrichment technique with endosulfan as sole carbon source, consortium CE was found to be the most efficient with 72% and 87% degradation of alpha-endosulfan and beta-endosulfan, respectively, in 20 days. In soil microcosm, consortium AE, BE and CE degraded alpha-endosulfan by 57%, 88% and 91%, respectively, whereas beta-endosulfan was degraded by 4%, 60% and 67% after 30 days. Ochrobacterum sp., Arthrobacter sp., and Burkholderia sp., isolated and identified on the basis of 16s rDNA gene sequence, individually showed in situ biodegradation of alpha-endosulfan in contaminated soil microcosm by 61, 73, and 74, respectively, whereas degradation of beta-endosulfan was 63, 75, and 62, respectively, after 6 weeks of incubation over the control which showed 26% and 23 % degradation of alpha-endosulfan and beta-endosulfan, respectively. Population survival of Ochrobacterum sp., Arthrobacter sp., and Burkholderia sp., by plate count on Luria Broth with carbenicillin showed 75-88% survival of these isolates as compared to 36-48% of survival obtained from PCR fingerprinting. Arthrobacter sp. oxidized endosulfan to endosulfan sulfate which was further metabolized but no known metabolite of endosulfan sulfate was detected.     

Biodegradation of atrazine in sand sediments and in a sand-filter

The potential of a microbial consortium for treating waters contaminated with atrazine was considered. In conventional liquid culture, atrazine and its two dealkylated by-products were equally metabolised by the microbial consortium. Transient production of hydroxyatrazine was observed during atrazine catabolism, indicating that the catabolic pathway was similar to the one reported for isolates capable of atrazine mineralisation. This consortium was then inoculated to sediments sampled from an artificial recharge site. These sediments were contaminated by atrazine and diuron and exhibited only a slow endogenous herbicide dissipation. Inoculated microorganisms led to extensive atrazine degradation and survived for more than 10 weeks in the sediments. A rudimentary bioreactor was then setup using a soil core originating from the same recharge site. Degrading microorganisms rapidly colonised the core and expressed their degrading activity. The efficiency of the bioreactor was improved in the presence of spiked environmental surface waters. Atrazine degraders thus possibly benefited from the other organic sources in developing and expressing their activity. The microbial consortium did not initially exhibit the capacity to degrade diuron, which was used as reference compound. No change in this characteristic was detected throughout the study. Received: 13 December 1999 / Received revision: 26 April 2000 / Accepted: 5 May 2000