Mineralisation of the herbicide linuron by Variovorax sp. strain RA8 isolated from Japanese river sediment using an ecosystem model (microcosm)

BACKGROUND: Linuron is a globally used phenylurea herbicide, and a large number of studies have been made on the microbial degradation of the herbicide. However, to date, the few bacteria able individually to mineralise linuron have been isolated only from European agricultural soils. An attempt was made to isolate linuron‐mineralising bacteria from Japanese river sediment using a uniquely designed river ecosystem model (microcosm) treated with ¹⁴C‐ring‐labelled linuron (approximately 1 mg L^?1). RESULTS: A linuron‐mineralising bacterium that inhabits river sediment was successfully isolated. The isolate belongs to the genera Variovorax and was designated as strain RA8. Strain RA8 gradually used linuron in basal salt medium (5.2 mg L^?1) with slight growth. In 15 days, approximately 25% of ¹⁴C‐linuron was mineralised to ¹⁴CO₂, with 3,4‐dichloroaniline as an intermediate. Conversely, in 100‐fold diluted R2A broth, strain RA8 rapidly mineralised ¹⁴C‐linuron (5.5 mg L^?1) and more than 70% of the applied radioactivity was released as ¹⁴CO₂ within 3 days, and a trace amount of 3,4‐dichloroaniline was detected. Additionally, the isolate also degraded monolinuron, metobromuron and chlorobromuron, but not diuron, monuron or isoproturon. CONCLUSION: Although strain RA8 can grow on linuron, some elements in the R2A broth seemed significantly to stimulate its growth and ability to degrade. The isolate strictly recognised the structural difference between N‐methoxy‐N‐methyl and N,N‐dimethyl substitution of various phenylurea herbicides. Copyright © 2010 Society of Chemical Industry     

Evidence for the Accelerated Degradation of Isoproturon in Soils

The herbicide isoproturon was degraded rapidly in a sandy loam soil under laboratory conditions (incubation temperature, 15°C; soil moisture potential, -33 kPa). Degradation was inhibited following treatment of the soil with the antibiotic chloramphenicol, but unaffected by treatment with cycloheximide, thus indicating an involvement of soil bacteria. Rapid degradation was not observed with other phenylurea herbicides, such as diuron, linuron, monuron or metoxuron incubated in the same soil under the same experimental conditions. Three successive applications of isoproturon to ten soils differing in their physicochemical properties and previous cropping history induced rapid degradation of the herbicide in most of them under laboratory conditions. There were, however, no apparent differences in ease of induction of rapid degradation between soils which had been treated with isoproturon for the last five years in the field and those with no pre-treatment history. A mixed bacterial culture able to degrade isoproturon in liquid culture was isolated from a soil in which the herbicide degraded rapidly.     

Anaerobic microbial degradation of selected 3,4-dihalogenated aromatic compounds

Anaerobic microbial degradation of selected 3,4-dihalogenated aromatic compounds was studied in medium inoculated with pond sediment. Sediment samples were collected from a diuron-treated pond. Diuron was dehalogenated at the para position, forming CPDMU as the sole degradation product. DCPU was similarly dehalogenated at the para position, forming MCPU as the only degradation product. Linuron degradation resulted in four products: one, CPMMU, was the result of biological dehalogenation at the para position; another, DCPMU, was the result of chemical degradation; and the other two products were unidentified. Chlorbromuron degradation formed three unidentified products. Stam, an acylanilide, was degraded, forming two products, one of which was possibly 3-chloropropioanilide. CIPC and an unidentified compound were formed from DCIP. No degradation of parent compounds or appearance of degradation products were detected in mixtures of each test compound and sterile sediment except linuron.     

Degradation of carbofuran by an enrichment culture developed from carbofuran-treated Azolla plot

Standing water from carbofuran-treated Azolla plots showing accelerated degradation was further enriched by five repeated transfers to carbofuran-supplemented mineral salts medium. This enrichment culture developed from standing water of carbofuran-treated Azolla plot can utilise carbofuran as sole source of carbon and nitrogen. The enrichment culture was able to hydrolyse nearly 100% of [ring-¹⁴C]carbofuran to carbofuran phenol in five days, which accumulated in the medium, while the carbamate side-chain in [carbonyl-¹⁴C]carbofuran was readily mineralized to [¹⁴C]carbon dioxide. Enrichment culture was able to degrade carbofuran up to 1000 µg ml⁻¹ levels in mineral salts medium with ease. © 1999 Society of Chemical Industry     

Residues in carrots treated with linuron

Investigations have been carried out on residues of linuron and its breakdown products in carrots sprayed with Jinuron at 1, 2, or 4 kg a.i./ha, 0, 19, 28, 36 or 60 days after sowing (up to 57 days before harvesting). The extracted residues were separated into three fractions by liquid-liquid partitioning: (a) linuron, (b) 3-(3,4-dichlorophenyi)-l-methoxyurea, 3-(3,4-dichlorophenyl)-l-methylurea, 3,4-di-chlorophenylurea and (c) 3,4-dichloroaniline. The compounds in each fraction were hydrolysed and the iodine derivative 1,2-dichloro-4-iodobenzene was formed by a Sandmeyer reaction between 3,4-dichloroaniline and iodide ion, followed by gas chromatography with electron capture detector. Only 5-13% of the extract-able residues were breakdown products. Most of the detectable residue (87-95%) was identified as linuron. The relative proportions of linuron and breakdown products in carrots at the time of harvest were not affected by the time of spraying or the interval between treatment and harvest.     

Control of Avena fatua and Fagopyrum tataricum with tank mixtures of linuron or linuron + MCPA and sequential applications of linuron, and post-emergence A. fatua herbicides

Linuron (0.21 and 0.28 kg/ha) and linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture with field rates of barban, difenzoquat and flamprop-methyl reduced the phytotoxicity of these herbicides to Avena fatua. When linuron was applied immediately following or 6 days after the A. fatua herbicides no reduction in phytotoxicity to A. fatua occurred, suggesting that the antagonism may be occurring as a result of physical or chemical incompatability when the herbicides are mixed together. The possibility of obtaining broad-spectrum weed control with one trip over the field by applying linuron and one of these wild oat herbicides separately but at the same time using a double-boom, double-tank system deserves evaluation. When linuron was applied in a tank mixture (0.21 and 0.28 kg/ha), immediately after, or 6 days after diclofop-methyl (0.70 kg/ha), there was no reduction of A. fatua control, and wheat tolerance to the tank mixture was good. This tank mixture offers potential for control under field conditions of A. fatua and some broad-leaved weeds in one spray operation. Linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture severely reduced A. fatua control with diclofop-methyl. No loss of phytotoxicity to Fagopyrum tataricum occurred when the A. fatua herbicides tested were tank mixed with linuron or linuron + MCPA. Lutte contre Avena fatua et Fagopyrum tataricum avec des mélanges extemporanés de linuron ou de linuron + MCPA et des applications successives de linuron et d'herbicides de postlevée actifs contre A. fatua     

Induction and Transfer of Enhanced Biodegradation of the Herbicide Napropamide in Soils

In laboratory incubations, the times to 50% loss (DT₅₀) of a first application of napropamide were approximately 25, 45 and 75 days in soil incubated at 25, 15 and 5°C respectively. When treated for a second time, the DT₅₀ values were 4, 7 and 15 days at the same temperatures, irrespective of the temperature of the first incubation. This indicates that enhanced degradation of napropamide in soil can be both induced and expressed at low temperature. A mixed microbial culture able to degrade the herbicide to a single degradation product, identified by HPLC retention time as naphthoxypropionic acid, was obtained from a soil capable of rapid degradation. Addition of a sub-sample of this mixed culture to a previously untreated soil introduced rapid degrading ability. When small amounts of soil capable of rapid degradation were added to previously untreated soil, in both the laboratory and the field, the degradation rate of napropamide increased compared with that in unamended soils.     

Growth of facultative anaerobic population of human intestinal bacteria with the carbamate pesticide aminocarb

The effect of different concentrations of the carbamate pesticide, aminocarb (Matacil), on the growth and selection of facultative anaerobic bacteria and degradation of the pesticide by human endoflora of the intestinal tract was examined in vitro. Microorganisms were cultured under aerobic or anaerobic conditions, in nutrient broth and mineral media. The intestinal population was more sensitive to 10–1000 μg/ml aminocarb under anaerobic conditions than in aerobic culture; however, spontaneous degradation of aminocarb in media markedly affected the degree of bacterial growth inhibition in prolonged cultures. In addition, the type of culture medium appeared to influence the degree of aminocarb-induced bacterial growth inhibition. A dose of aminocarb inducing 50% growth inhibition was established for different culture conditions: for mineral medium, aminocarb inhibited bacterial growth by 50% at 600 μg/ml under anaerobic and aerobic conditions, whereas less than 50% inhibition was observed even at 1000 μg/ml aminocarb when bacteria were grown in nutrient broth. A selection of bacterial strains occurred in the presence of increasing aminocarb concentrations, which was determined quantitatively and qualitatively by the identification of codominants. A shift in several Escherichia coli biotypes was also observed in cultures with aminocarb, in comparison to control cultures. Bacterial degradation of aminocarb, under anaerobic and aerobic conditions, was determined in a mixed population of the intestinal microflora by high-performance liquid chromatography analysis of culture media. Data showed that aminocarb can be quickly degraded by human intestinal bacteria at relatively high pesticide concentrations. Moreover, other HPLC data suggest rapid spontaneous degradation of aminocarb in neutral and slightly alkaline pH conditions characteristic of the human intestinal tract, which can effectively eliminate the pesticide. Therefore, aminocarb, at the concentrations used, does not seriously affect the bacterial microflora of the human gut.     

Degradation of the herbicide benzoylprop-ethyl in soil

The degradation of [¹⁴C] benzoyl prop ethyl (SUFFIX,^a ethyl N-benzoyl-N-(3,4-dichlorophenyl)-2-aminopropionate) in four soils has been studied under laboratory conditions. The major degradation product of benzoylprop ethyl at up to 4 months after treatment was its corresponding carboxylic acid (II). On further storage this compound became firmly bound to soil before it underwent a slow debenzoylation process which led to the formation of a number of products including N-3,4-dichlorophenylalanine (IV), benzoic acid, 3,4-dichloroaniline (DCA), which was mainly present complexed with humic acids, and other polar products. Although these polar products were not identified, they were probably degradation products of DCA, since they were also formed when DCA was added to soil. No 3,3′,4,4′-tetrachloroazobenzene (TCAB) was detected in any of the soils at limits of detectability ranging from 0.01-0.001 parts/million. Since N-3,4-dichlorophenylalanine (IV) and 3,4-dichloroaniline were transient degradation products of benzoylprop ethyl, the metabolism in soil of radiolabelled samples of these compounds was also studied. In these laboratory experiments the persistence of the herbicide increased as the organic matter content of the soil increased and the time for depletion of half of the applied benzoylprop ethyl varied from 1 week in sandy loam and clay loam soils to 12 weeks in a peat soil.     

Spatial variability in the mineralisation of the phenylurea herbicide linuron within a Danish agricultural field: multivariate correlation to simple soil parameters

The spatial variability in the mineralisation rate of linuron [N-(3,4-dichlorophenyl)-N'-methoxy-N'-methylurea] was studied within a previously treated Danish agricultural field by sampling soils from eleven different plots randomly distributed across an area of 20 x 20 m. The soils were characterised with respect to different abiotic and biotic properties including moisture content, organic matter content, pH, nutrient content, bacterial biomass, potential for mineralisation of MCPA [(4-chloro-2-methylphenoxy)acetic acid] and linuron. Five soils had a potential for mineralisation of linuron, with 5-15% of the added [ring-U-14C]linuron metabolised to 14CO2 within 60 days at 10 degrees C, while no extensive mineralisation of linuron was observed in the six remaining soils within this period. A TLC analysis of the methanol-extractable residues showed no development of 14C-labelled metabolites from linuron in any of the samples. Multivariate analysis was conducted to elucidate relationships between the intrinsic properties of single soil samples and initial rate of linuron mineralisation. The analysis indicated that important soil parameters in determining the spatial heterogeneity included the C(total)/N(total) ratio, pH and the water-extractable potassium contents, with the first of these highly negatively correlated and the last two highly positively correlated to the initial linuron mineralisation rate. This study shows that enhanced biodegradation of linuron may develop with successive field treatments, but that considerable in-field spatial heterogeneity in the degradation rate still exists. Combined with a parallel enrichment study focused on the underlying microbial processes, the present results suggest that intrinsic soil properties affect the linuron-metabolising bacterial population and thereby determine the spatial variability in the linuron mineralisation activity.     

The degradation of simazine, linuron and propyzamide in different soils

Simazine, linuron and propyzamide were incubated in 18 different soils at 25°C and field capacity soil moisture content. The degradation of each herbicide followed first-order kinetics. The half-life of simazine varied from 20 to 44 days, that of linuron from 22 to 86 days and that of propyzamide from 10 to 32 days. The rate of linuron degradation was highly significantly correlated with soil organic matter content, clay content, soil respiration and the extent of herbicide adsorption by the soil. The rate of simazine degradation was significantly and negatively correlated with soil pH, but the rate of propyzamide degradation was not related with any of the soil factors examined.     

Bioconversion of dieldrin by wood‐rotting fungi and metabolite detection

BACKGROUND: Dieldrin is one of the most persistent organochlorine pesticides, listed as one of the 12 persistent organic pollutants in the Stockholm Convention. Although microbial degradation is an effective way to remediate environmental pollutants, reports on aerobic microbial degradation of dieldrin are limited. Wood‐rotting fungi can degrade a wide spectrum of recalcitrant organopollutants, and an attempt has been made to select wood‐rotting fungi that can degrade dieldrin, and to identify the metabolite. RESULTS: Thirty‐four isolates of wood‐rotting fungi were investigated for their ability to degrade dieldrin. Strain YK543 degraded 39.1 ± 8.8% of dieldrin during 30 days of incubation. Phylogenetic analysis demonstrated that strain YK543 was closely related to the fungus Phlebia brevispora Nakasone TMIC33929, which has been reported as a fungus that can degrade chlorinated dioxins and polychlorinated biphenyls. 9‐Hydroxydieldrin was detected as a metabolite in the cultures of strain YK543. CONCLUSION: It is important to select the microorganisms that degrade organic pollutants, and to identify the metabolic pathway for the development of bioremediation methods. Strain YK543 was selected as a fungus capable of degrading dieldrin. The metabolic pathway includes 9‐hydroxylation reported in rat's metabolism catalysed by liver microsomal monooxygenase. This is the first report of transformation of dieldrin to 9‐hydroxydieldrin by a microorganism. Copyright © 2010 Society of Chemical Industry     

Evidence for the enhanced biodegradation of napropamide in soil

In laboratory incubations, the time to 50% loss of napropamide was approximately 60; 21 and 8 days in soil treated for the first, second and third time respectively. In a survey of soils from commercial fields, there was evidence that enhanced biodegradation of the compound had been induced by normal field applications—in some soils by a single previous treatment. Confirmation of the observations of rapid rates of loss in pre-treated soil was obtained in experiments with three formulations of napropamide. The rate of degradation in enhanced soils was unaffected by treatment of the soils with the antifungal antibiotic cycloheximide, but was inhibited by the antibacterial antibiotic chloramphenicol. Mixed bacterial cultures able to degrade the herbicide were obtained from three rapid-degrading soils by enrichment culture. Isolates from two of them were able to degrade the herbicide in pure culture. These bacteria have, as yet, not been characterised.     

Joint action of root-absorbed mixtures of DPX-4189* and linuron in Sinapis alba L. and barley

The joint action of DPX-4189* (2 chloro-N-[(4-methoxy-6-methyl-1, 3, 5-triazin-2-yl)-aminocarbonyl] benzenesulfonamide) and linuron (N-[3, 4-dichlorophenyl]-N-methoxy-N-methylurea) mixtures, applied in fixed ratios of 1:15 and 1:30, was assessed using water culture experiments in growth chambers. The dose-response curves of DPX-4189 were fiat compared with these of linuron. At Gr₅₀-level (the dose required to reduce dry matter by 50% relative to the untreated control), DPX-4189 was 12-fold more potent in Sinapis alba than was linuron, whereas the potencies of the two compounds were almost similar in barley. The selectivity indices (Gr₈₀[barley]/Gr₂₀[S. alba]) of DPX-4189 and linuron were 3.1 and 1.8. In both species the mixtures were less active than expected from an additive dose model, and the detracted efficacy of the mixtures was of almost similar magnitude. The results indicated that if S. alba is regarded a weed, the loss of bioactivity of the mixtures may be compensated by some increase in dose rate without injuring the barley crop.     

Factors influencing rates of degradation of an arylamide and a benzoic acid in subsoils

The kinetics of fundamental reactions (hydrolytic, oxidative and reductive) involved in the degradation of organic compounds such as pesticides in subsoils were investigated using the model compounds N‐(4‐nitrophenyl)propanamide and 4‐nitrobenzoic acid. The rates of hydrolysis of N‐(4‐nitrophenyl)propanamide were also measured in aqueous buffers, hydrolysis being extremely slow at neutral pH; its degradation in three soils was by microbially mediated hydrolysis, being very much faster than aqueous hydrolysis at the same pH. Rates of degradation of N‐(4‐nitrophenyl)propanamide in subsoils were initially up to thirty times slower than those in topsoil, and in some subsoils degradation showed a marked lag‐phase of between 72–144 h. For 4‐nitrobenzoic acid, a similar lag‐phase of slow degradation, followed by a phase of rapid degradation, was observed in both topsoils and subsoils. Remarkably, the rapid phases of degradation in subsoils often approached rates occurring in the corresponding topsoil. No reduction of the nitro group on either compound was observed, even in a water‐saturated subsoil. Sometimes there were differences in the length of the lag‐phases measured for replicate samples of subsoils; also, application of lower concentrations of 4‐nitrobenzoic acid generally gave rise to shorter lag‐phases. Partial sterilization of soils by azide greatly slowed breakdown of both compounds, confirming the important role of microbial degradation. Such behaviour is consistent with the variable build‐up of populations of micro‐organisms able to degrade the compound, smaller populations being able to deal rapidly with the lower concentrations. After applying a second dose of 4‐nitrobenzoic acid to soil, degradation was rapid but initially not as fast as the final rates during breakdown of the first treatment. Hence, soil may only partially retain the ability to degrade previously applied xenobiotics. Nonetheless it is noteworthy that, even in deep subsoils, indigenous microbial populations can rapidly adapt to degrade certain small organic molecules. © 2000 Society of Chemical Industry     

Isolation of a phytotoxic isocoumarin from Diaporthe eres‐infected Hedera helix (English ivy) and synthesis of its phytotoxic analogs

BACKGROUND

The fungus Diaporthe eres was isolated from a fungal pathogen‐infected leaf of Hedera helix (English ivy) exhibiting necrosis. It is hypothesized that the causative fungus produces phytotoxins as evidenced by necrotic lesions on the leaves.

RESULTS

The fungus was isolated and grown in Czapek Dox broth culture medium and potato dextrose broth culture medium and identified as Diaporthe eres. The ethyl acetate extracts of the culture broths were phytotoxic to lettuce (Lactuca sativa) and bentgrass (Agrostis stolonifera). 3,4‐Dihydro‐8‐hydroxy‐3,5‐dimethylisocoumarin ( 1 ) and tyrosol ( 2 ) were isolated and identified as the phytotoxic constituents. Six analogs of 3,4‐dihydro‐isocoumarin were synthesized and shown to be phytotoxic. The synthesized 3,4‐dihydro‐8‐hydroxy‐3,7‐dimethylisocoumarin and 3,4‐dihydro‐8‐hydroxy‐3,3,7‐trimethylisocoumarin were two‐ to three‐fold more phytotoxic than the naturally occurring 1 in a Lemna paucicostata growth bioassay.

CONCLUSION

Synthesis and herbicidal activities of the several new analogs of 1 are reported for the first time. These promising molecules should be used as templates for synthesis and testing of more analogs. © 2017 Society of Chemical Industry     

Multiplication of isolate R-5 of <Emphasis Type="Italic">Streptomyces galbus</Emphasis> on rhododendron leaves and its production of cell wall-degrading enzymes

 An endophytic actinomycete, isolate R-5 of Streptomyces galbus Frommer, that has promising potential as a biocontrol agent was originally isolated from field-grown rhododendron. In this study, the mode of entry of R-5 into leaves of tissue-cultured seedlings of rhododendron was investigated in connection with its production of cell wall-degrading enzymes. Light and scanning electron microscopy (SEM) revealed that R-5 grew on leaf surfaces and entered leaf tissues via stomata and that the internal mycelia grew out of stomata after colonization in host tissues. Micromanipulation at the SEM level demonstrated a prominent depression in the host surface at the interfaces with the mycelia, suggesting that such a depression could be caused by degradation of cell wall components by hydrolytic enzymes secreted from R-5 mycelia. In subsequent plate assays, R-5 produced cellulase, pectinase, xylanase, and nonspecific esterase when cultured in liquid medium. Moreover, R-5 multiplied in mineral medium containing cellulose, pectin, or xylan as a single carbon source. Thus, R-5 mycelia could degrade host cell walls at contact sites and probably utilize the degradation products as carbon sources. Received: May 16, 2002 / Accepted: July 9, 2002     

Metabolism of the pesticide metabolites 4-nitrophenol and 3,4-dichloroaniline in carrot (Daucus carota) cell suspension cultures

The metabolism of [ 14 C]-4-nitrophenol and [ 14 C]-3,4-dichloroaniline (the xenobiotics are degradation products of parathion and propanil, respectively) was studied in cell suspension cultures of carrot (Daucus carota L.). 4-Nitrophenol was transformed almost quantitatively to water-soluble conjugates with minor amounts of non-extractable residues. The conjugates identified were 1-(O-β-D-glucopyranosyl)-4-nitrobenzene and 1-(6′-O-malonyl-O-β-D-glucopyranosyl)-4-nitrobenzene. In addition, two unidentified metabolites were observed, possibly a disaccharide and another malonylated glycoside of 4-nitrophenol. Time-course studies demonstrated that 4-nitrophenol was rapidly taken up and conjugated; all metabolites remained associated with the cells rather than nutrient medium. 3,4-Dichloroaniline was transformed quantitatively to water-soluble conjugates and bound residues (3.6%). The water-soluble metabolites were identified as 6′-O-malonyl-N-(β-D-glucopyranosyl)-3,4-dichloroaniline, N-(β-D-glucopyranosyl)-3,4-dichloroaniline and N-malonyl-3,4-dichloroaniline. A time-course study showed that the glucosides were formed initially, then decreased, possibly due to hydrolysis. This decrease was paralleled by an increase of the main metabolite, N-malonyl-3,4-dichloroaniline, which was predominantly recovered from the medium.     

The effect of nutrients on the decomposition of the herbicides atrazine and linuron incubated with soil

The rates of disappearance of atrazine and linuron when incubated at 22°C with soil or soil containing added nutrient materials were determined with 2 contrasting soils. Inorganic salts, straw or a combination of both increased atrazine degradation in both soils. None of the treatments influenced linuron breakdown greatly. It is concluded that in these soils the rate limiting step in atrazine degradation could be microbiological, not chemical.     

Enhanced degradation of some soil-applied herbicides

In a field experiment involving repeated herbicide application, persistence of simazine was not affected by up to three previous doses of the herbicide. With propyzamide, there was a trend to more rapid rates of degradation with increasing number of previous treatments. Persistence of linuron and alachlor was affected only slightly by prior applications. In a laboratory incubation with soil from the field that had received four doses of the appropriate herbicide over a 12–month period, there was again no effect from simazine pretreatments on rates of loss. However, propyzamide, linuron and alachlor all degraded more rapidly in the previously treated than in similar untreated soil samples. Propyzamide, linuron, alachlor and napropamide degradation rates were all enhanced by a single pretreatment of soil in laboratory incubations, whereas degradation rates of isoproturon, metazachlor, atrazine and simazine were the same in pretreated and control soil samples.