Stimulation or inhibition: Leaf microbial decomposition in streams subjected to complex chemical contamination.

Leaf litter decomposition is a key mechanism in headwater streams, allowing the transfer of nutrients and energy into the entire food web. However, chemical contamination resulting from human activity may exert a high pressure on the process, possibly threatening the structure of heterotrophic microbial communities and their decomposition abilities. In this study, the rates of microbial Alnus glutinosa (Alnus) leaf decay were assessed in six French watersheds displaying different land use (agricultural, urbanized, forested) and over four seasons (spring, summer, autumn, winter).

Biodegradation and toxicity of a maize herbicide mixture: mesotrione, nicosulfuron and S-metolachlor.

The prediction of chemical mixture toxicity is a major concern regarding unintentional mixture of pesticides from agricultural lands treated with various such compounds. We focused our work on a mixture of three herbicides commonly applied on maize crops within a fortnight, namely mesotrione (β-triketone), nicosulfuron (sulfonylurea) and S-metolachlor (chloroacetanilide). The metabolic pathways of mesotrione and nicosulfuron were qualitatively and quantitatively determined with a bacterial strain (Bacillus megaterium Mes11).

Identification of sulfonylurea biodegradation pathways enabled by a novel nicosulfuron-transforming strain Pseudomonas fluorescens SG-1: Toxicity assessment and effect of formulation.

Nicosulfuron is a selective herbicide belonging to the sulfonylurea family, commonly used on maize culture. A bacterial strain SG-1 was isolated from an agricultural soil previously treated with nicosulfuron. This strain was identified as Pseudomonas fluorescens and is able to quantitatively dissipate 77.

Functional and structural responses of soil N-cycling microbial communities to the herbicide mesotrione: a dose-effect microcosm approach.

Microbial communities driving the nitrogen cycle contribute to ecosystem services such as crop production and air, soil, and water quality. The responses to herbicide stress of ammonia-oxidizing and ammonia-denitrifying microbial communities were investigated by an analysis of changes in structure-function relationships. Their potential activities, abundances (quantitative PCR), and genetic structure (denaturing gradient gel electrophoresis) were assessed in a microcosm experiment.

Soil surface colonization by phototrophic indigenous organisms, in two contrasted soils treated by formulated maize herbicide mixtures.

Soil phototrophic microorganisms, contributors to soil health and food webs, share their particular metabolism with plants. Current agricultural practices employ mixtures of pesticides to ensure the crops yields and can potentially impair these non-target organisms. However despite this environmental reality, studies dealing the susceptibility of phototrophic microorganisms to pesticide mixtures are scarce.

Toxicity assessment of the maize herbicides S-metolachlor, benoxacor, mesotrione and nicosulfuron, and their corresponding commercial formulations, alone and in mixtures, using the Microtox(®) test.

The Microtox(®) test, using the prokaryote Vibrio fischeri, was employed to assess the toxicity of the maize herbicides S-metolachlor, benoxacor, mesotrione and nicosulfuron, and their formulated compounds: Dual Gold Safeneur(®), Callisto(®) and Milagro(®); alone and in mixtures. For each compound we obtained original IC50 values, with consistent higher toxicities for formulated compounds compared to active ingredients alone. Mixtures of the four herbicides, prepared according to application doses encountered in agriculture, were found to be toxic at a lower concentration than single molecules.

Dose-dependent effects of the herbicide mesotrione on soil cyanobacterial communities.

This study aimed to investigate the dose-response effects of an herbicide on soil photosynthetic microbial communities, particularly cyanobacteria, using a microcosm approach. Pure mesotrione (active ingredient), and Callisto (a commercial formulation of this triketone herbicide), were spread at different rates on soil microcosm surfaces. Soil Chlorophyll concentrations were quantified to assess the photosynthetic biomass, and the genetic structure and diversity of the cyanobacterial community were investigated by a group-specific polymerase chain reaction followed by denaturing gradient gel electrophoresis.

Ecotoxicological effects of diuron and chlorotoluron nitrate-induced photodegradation products: monospecific and aquatic mesocosm-integrated studies.

The ecotoxicological impact of nitrate-induced photodegradation products of diuron and chlorotoluron was studied through monospecific biotests conducted in conjunction with experiments in outdoor aquatic mesocosms. Organisms representing three trophic levels were used: two heterotrophic microorganisms, the luminescent bacterium Vibrio fischeri and the ciliated protozoa Tetrahymena pyriformis, and one metazoa, the gastropod Lymnaea stagnalis. Among the variety of the phenylurea photoproducts, the N-formylated ones appeared clearly more toxic than the parent compounds towards the microorganisms, whereas the nitroderivatives showed a similar toxicity.

Sunlight nitrate-induced photodegradation of chlorotoluron: evidence of the process in aquatic mesocosms.

The nitrate-induced photodegradation of chlorotoluron was demonstrated to occur efficiently in natural water through two series of experiments in outdoor aquatic mesocosms. During the first campaign, it was shown that the pesticide degradation kinetics was clearly dependent on nitrate concentration. This parameter also influenced the accumulation of the first- and second-generation byproducts, including predominantly N-terminus oxidation products and nitro-derivatives of the phenyl ring.

Photolysis of the herbicide sulcotrione: formation of a major photoproduct and its toxicity evaluation.

Background: Sulcotrione is a selective herbicide marketed for use in maize since 1993, but its environmental fate is not yet fully elucidated. A major metabolite resulting from cleavage between the two ring moieties, leading to 2-chloro-4-mesylbenzoic acid (CMBA), has been identified; it presents a rather low toxicity. In photochemical studies this compound has also been claimed to be formed in high proportions.

Toxicity assessment of the herbicides sulcotrione and mesotrione toward two reference environmental microorganisms: Tetrahymena pyriformis and Vibrio fischeri.

The potential toxicity of sulcotrione (2-[2-chloro-4-(methylsulfonyl)benzoyl]-1,3-cyclohexanedione) and mesotrione (2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione), two selective triketonic herbicides, was assessed using representative environmental microorganisms frequently used in ecotoxicology: the eukaryote Tetrahymena pyriformis and the prokaryote Vibrio fischeri. The aims were also to evaluate the toxicity of different known degradation products, to compare the toxicity of these herbicides with that of atrazine, and to assess the toxicity of the commercial herbicidal products Mikado and Callisto. Toxicity assays involved the Microtox test, the T.

Longitudinal changes in microbial planktonic communities of a French river in relation to pesticide and nutrient inputs.

To determine the effects of anthropic activities on river planktonic microbial populations, monthly water samples were collected for 11 months from two sampling sites characterized by differing nutrient and pesticide levels. The difference in trophic level between the two stations was particularly pronounced from May to November. Total pesticide concentrations were notably higher at the downstream station from April to October with a clear predominance of herbicide residues, especially the glyphosate metabolite aminomethylphosphonic acid (AMPA).

Assessment of the potential toxicity of herbicides and their degradation products to nontarget cells using two microorganisms, the bacteria Vibrio fischeri and the ciliate Tetrahymena pyriformis.

The potential toxicity of several herbicides-alachlor, diuron and its photo and biotransformation products, glyphosate and its metabolite aminomethyl phosphonic acid (AMPA)-to nontarget cells was assessed using two microorganisms frequently used in ecotoxicology, Vibrio fischeri and Tetrahymena pyriformis. Toxicity assays involved the Microtox test, the T. pyriformis population growth impairment test employing three different processes (flasks, tubes, microplates), and the T.

Effect of Methanobrevibacter sp MF1 inoculation on glycoside hydrolase and polysaccharide depolymerase activities, wheat straw degradation and volatile fatty acid concentrations in the rumen of gnotobiotically-reared lambs.

Four naturally born lambs were placed in sterile isolators 24 h after birth before the natural establishment of cellulolytic microorganisms and archaea methanogens. At the age of 6 weeks they were inoculated with pure cultures of the strains FD1 and 007 of Ruminococcus flavefaciens and at the age of 4 months with a pure culture of Methanobrevibacter sp. MF1.

Effects of the phenylurea herbicide diuron on natural riverine microbial communities in an experimental study.

The effects of the phenylurea herbicide diuron (10 microgl(-1)) on natural riverine microbial communities were investigated using a three-week laboratory microcosm study. During the first six days, a latency period was observed both in the algal and the bacterial communities despite favorable abiotic conditions and independently of diuron exposure. From the second week, an intense algal bloom (chlorophyll a concentrations and cell abundances) was observed in the uncontaminated microcosms but not in the treated microcosms.

Influence of UV irradiation on the toxicity of phenylurea herbicides using Microtox test.

Halogenated phenylurea herbicides are not very toxic by themselves to animals, but their exposure to UV light may significantly increase the toxicity of their solutions. Absorption of light may indeed induce a phototransformation of the herbicide with a possible formation of more toxic intermediate photoproducts. Fortunately in environmental conditions photolysis is usually slow and photoproducts do not accumulate appreciably.

Sequential bio- and phototransformation of the herbicide methabenzthiazuron in water.

We investigated the transformation of methabenzthiazuron in water by microorganisms and solar light. This compound was very slowly phototransformed when irradiated at lambda > 290 nm, but it could be successfully oxidized into 6-hydroxymethabenzthiazuron by Aspergillus niger, as shown by nuclear magnetic resonance experiments. The toxicity of this metabolite, as determined by the standardized Microtox test, was sixfold lower than that of the parent molecule.

Iron(III) photo-induced degradation of isoproturon: correlation between degradation and toxicity.

The degradation of isoproturon photoinduced by Fe(III) was investigated under both artificial and solar light. The monomeric species Fe(OH)2+ present under the experimental conditions ([Fe(III)] = 3 x 10(-4) M) is the main Fe(III) species responsible for the degradation of isoproturon. The process involves the attack on the pollutant by OH radicals generated by irradiation of Fe(OH)2+.

Biotransformation of phenylurea herbicides by a soil bacterial strain, Arthrobacter sp. N2: structure, ecotoxicity and fate of diuron metabolite with soil fungi.

In order to assess the influence of the aromatic substitution on the ability of a soil bacterial strain, Arthrobacter sp. N2, to degrade phenylurea herbicides, biotransformation assays were performed in mineral medium with resting cells of this soil bacterial strain on three phenylurea herbicides (diuron, chlorotoluron and isoproturon). Each herbicide considered, led to the formation of only one metabolite detected by HPLC analysis.

Use of the ciliated protozoan Tetrahymena pyriformis for the assessment of toxicity and quantitative structure--activity relationships of xenobiotics: comparison with the Microtox test.

Cytotoxicity and quantitative structure-activity relationships of 13 inorganic and 21 organic substances were determined using three bioassays performed on the ciliated protozoan Tetrahymena pyriformis and the luminescent bacterium Vibrio fischeri. The best concordance of toxicity results was observed between the T. pyriformis FDA--esterase activity and population growth inhibition tests for the organic compounds.

Degradation products of a phenylurea herbicide, diuron: synthesis, ecotoxicity, and biotransformation.

The degradation products of diuron (photoproducts and metabolites), already described in the literature, were synthesized in order to carry out further investigations. Their ecotoxicity was determined using the standardized Microtox test, and most of the derivatives presented a nontarget toxicity higher than that of diuron. Therefore, the biotransformation of these compounds was tested with four fungal strains and a bacterial strain, which were known to be efficient for diuron transformation.

A new low-cost microbiotest with the Protozoan spirostomum teres: culture conditions and assessment of sensitivity of the ciliate to 14 pure chemicals.

This paper defines the culture conditions of the ciliate Spirostomum teres and assesses its sensitivity to some xenobiotics for the development of a new low-cost microbiotest. The model was selected for its ubiquitous distribution, large size for a unicellular species, easy culture in holoxenic medium, moderate generation time, and high sensitivity to pure toxicants. The influence of different culture waters, inocula of ciliates, food, temperature, light, and darkness on the growth of the ciliate population was tested.

Quantitative determination of H2-utilizing acetogenic and sulfate-reducing bacteria and methanogenic archaea from digestive tract of different mammals.

Total number of bacteria, cellulolytic bacteria, and H2-utilizing microbial populations (methanogenic archaea, acetogenic and sulfate-reducing bacteria) were enumerated in fresh rumen samples from sheep, cattle, buffaloes, deer, llamas, and caecal samples from horses. Methanogens and sulfate reducers were found in all samples, whereas acetogenes were not detected in some samples of each animal. Archaea methanogens were the largest H2-utilizing populations in all animals, and a correlation was observed between the numbers of methanogens and those of cellulolytic microorganisms.

Effect of anaerobic fungi on glycoside hydrolase and polysaccharide depolymerase activities, in sacco straw degradation and volatile fatty acid concentrations in the rumen of gnotobiotically reared lambs.

Four naturally born lambs were placed in sterile isolators 24 h after birth, before the natural establishment of the cellulolytic microorganisms. At the age of 4 weeks, a cellulolytic bacterial population of approximately 10(8) cells g-1 of rumen contents was established by inoculation with a 10(-6) dilution of ruminal contents taken from an adult sheep. A pure culture of Neocallimastix frontalis MCH3 and Piromyces communis FL was inoculated into the rumen 5 months after birth and a stable population of 10(3)-10(4) zoospores g-1 developed; the cellulolytic bacteria and fungi established populations in the 4 lambs that were similar to those observed in conventional animals.

In vitro study of the proteolytic activity of rumen anaerobic fungi.

Proteolytic, aminopeptidase, endopeptidase and carboxypeptidase activities of seven strains of rumen anaerobic fungi, selected to represent the fungal population commonly found in the rumen, were investigated in vitro. Whatever the nitrogen source included in the culture medium, a proteolytic activity against the 14C-labelled casein was detected in only one fungal strain. This strain belonged to the genus Piromyces.