Chlordecone-contaminated epilithic biofilms show increased adsorption capacities.

The rivers of Guadeloupe and Martinique (French West Indies) show high levels of chlordecone (CLD) contamination. This persistent molecule has a dramatic impact on both aquatic ecosystems and human health. In these rivers, epilithic biofilms are the main endogenous primary producers and represent a central food source for fish and crustaceans. Recently, their viscoelastic properties have been shown to be effective in bio-assessing pollution in tropical environments. As these properties are closely related to the biochemical composition of the biofilms, biochemical (fatty acids, pigments, extracellular polymeric substances (EPS) monosaccharides) and molecular markers (T-RFLP fingerprints of bacteria, archaea and eukaryotes) were investigated. Strong links between CLD pollution and both biofilm biochemistry and microbial community composition were found. In particular, high levels of CLD were linked with modified exo-polysaccharides corresponding to carbohydrates with enhanced adsorption and adhesion properties. The observed change probably resulted from a preferential interaction between CLD and sugars and/or a differential microbial secretion of EPS in response to the pollutant. These changes were expected to impact viscoelastic properties of epilithic biofilms highlighting the effect of CLD pollution on biofilm EPS matrix. They also suggested that microorganisms implement a CLD scavenging strategy, providing new insights on the role of EPS in the adaptation of microorganisms to CLD-polluted environments.

Effect of sulfonylurea tribenuron methyl herbicide on soil Actinobacteria growth and characterization of resistant strains

ABSTRACT Repeated application of pesticides disturbs microbial communities and cause dysfunctions on soil biological processes. Granstar® 75 DF is one of the most used sulfonylurea herbicides on cereal crops; it contains 75% of tribenuron-methyl. Assessing the changes on soil microbiota, particularly on the most abundant bacterial groups, will be a useful approach to determine the impact of Granstar® herbicide. For this purpose, we analyzed Actinobacteria, which are known for their diversity, abundance, and aptitude to resist to xenobiotic substances. Using a selective medium for Actinobacteria, 42 strains were isolated from both untreated and Granstar® treated soils. The number of isolates recovered from the treated agricultural soil was fewer than that isolated from the corresponding untreated soil, suggesting a negative effect of Granstar® herbicide on Actinobacteria community. Even so, the number of strains isolated from untreated and treated forest soil was quite similar. Among the isolates, resistant strains, tolerating high doses of Granstar® ranging from 0.3 to 0.6% (v/v), were obtained. The two most resistant strains (SRK12 and SRK17) were isolated from treated soils showing the importance of prior exposure to herbicides for bacterial adaptation. SRK12 and SRK17 strains showed different morphological features. The phylogenetic analysis, based on 16S rRNA gene sequencing, clustered the SRK12 strain with four Streptomyces type strains (S. vinaceusdrappus, S. mutabilis, S. ghanaensis and S. enissocaesilis), while SRK17 strain was closely related to Streptomyces africanus. Both strains were unable to grow on tribenuron methyl as unique source of carbon, despite its advanced dissipation. On the other hand, when glucose was added to tribenuron methyl, the bacterial development was evident with even an improvement of the tribenuron methyl degradation. In all cases, as tribenuron methyl disappeared, two compounds were detected with increased concentrations. These by-products appeared to be persistent and were not degraded either chemically or by the studied strains. Based on these observations, we suggested that bacterial activity on carbon substrates could be directly involved in the partial breakdown of tribenuron methyl, by generating the required acidity for the first step of the hydrolysis. Such a process would be interesting to consider in bioremediation of neutral and alkaline tribenuron methyl-polluted soils.

Effect of sulfonylurea tribenuron methyl herbicide on soil Actinobacteria growth and characterization of resistant strains.

Repeated application of pesticides disturbs microbial communities and cause dysfunctions on soil biological processes. Granstar® 75 DF is one of the most used sulfonylurea herbicides on cereal crops; it contains 75% of tribenuron-methyl. Assessing the changes on soil microbiota, particularly on the most abundant bacterial groups, will be a useful approach to determine the impact of Granstar® herbicide. For this purpose, we analyzed Actinobacteria, which are known for their diversity, abundance, and aptitude to resist to xenobiotic substances. Using a selective medium for Actinobacteria, 42 strains were isolated from both untreated and Granstar® treated soils. The number of isolates recovered from the treated agricultural soil was fewer than that isolated from the corresponding untreated soil, suggesting a negative effect of Granstar® herbicide on Actinobacteria community. Even so, the number of strains isolated from untreated and treated forest soil was quite similar. Among the isolates, resistant strains, tolerating high doses of Granstar® ranging from 0.3 to 0.6% (v/v), were obtained. The two most resistant strains (SRK12 and SRK17) were isolated from treated soils showing the importance of prior exposure to herbicides for bacterial adaptation. SRK12 and SRK17 strains showed different morphological features. The phylogenetic analysis, based on 16S rRNA gene sequencing, clustered the SRK12 strain with four Streptomyces type strains (S. vinaceusdrappus, S. mutabilis, S. ghanaensis and S. enissocaesilis), while SRK17 strain was closely related to Streptomyces africanus. Both strains were unable to grow on tribenuron methyl as unique source of carbon, despite its advanced dissipation. On the other hand, when glucose was added to tribenuron methyl, the bacterial development was evident with even an improvement of the tribenuron methyl degradation. In all cases, as tribenuron methyl disappeared, two compounds were detected with increased concentrations. These by-products appeared to be persistent and were not degraded either chemically or by the studied strains. Based on these observations, we suggested that bacterial activity on carbon substrates could be directly involved in the partial breakdown of tribenuron methyl, by generating the required acidity for the first step of the hydrolysis. Such a process would be interesting to consider in bioremediation of neutral and alkaline tribenuron methyl-polluted soils.

Isolation, purification and chemical characterization of a new angucyclinone compound produced by a new halotolerant Nocardiopsis sp. HR-4 strain.

A halotolerant Actinobacteria strain HR-4 was isolated from a salt lake soil sample in Algerian Sahara. Analysis of 16S rDNA gene sequence showed that strain HR-4 belonged to the genus Nocardiopsis. The similarity level ranges between 97.45 and 99.20% with Nocardiopsis species and Nocardiopsis rosea being the most closely related one. Morphological, physiological and phylogenetic characteristics comparisons showed significant differences with the nearest species. These data strongly suggest that strain HR-4 represents novel species. The antimicrobial activity of strain HR-4 showed an antibacterial activity against Gram-positive bacteria as well as an antifungal one. Two major natural products including a new one were isolated from the culture broth using various separation and purification procedures. The chemical structure established on the basis of spectroscopic studies NMR and by comparing with spectroscopic data from the literature of the two compounds affirm that they are classified in the group of Angucyclinones. This is the first report of a production of this type of molecules by the genus Nocardiopsis. The new natural compound was established as (-)-7-deoxy-8-O-methyltetrangomycin with a new configuration.

Removal of alachlor in anoxic soil slurries and related alteration of the active communities.

Despite the implication of anaerobic soil communities in important functions related to C and N biogeochemical cycles, their responses to pesticides are rarely assessed. This study focused on the impact of alachlor, a chloroacetanilide herbicide, on two agricultural soils differing in their land use (fallow and corn-cultivated) in order to investigate the potential adaptation of anaerobic or facultative anaerobic soil microorganisms from fields with long history of herbicide use. The experiment was performed by developing slurries in anoxic conditions over 47 days. Changes in the community structure assessed through terminal restriction fragment length polymorphism analysis of 16S rRNA genes clearly showed a shift in the bacterial community of the cultivated soil, whereas the modification of the microbial community of the fallow soil was delayed. In addition, the analysis of alachlor degradation capacities of the two anaerobic communities indicated that 99 % of alachlor was removed in anoxic slurries of cultivated soil. Both these results suggested the preexistence of microorganisms in the cultivated soil able to respond promptly to the pesticide exposure. The composition of the anaerobic active community determined by 16S rRNA transcript analysis was mainly composed of strictly anaerobic Clostridia and the facultative anaerobe Bacilli classes. Some genera, described for their role in herbicide biodegradation were active in alachlor-treated slurries, whereas others were no longer detected. Finally, this study highlights, when triggered, the important diversity of the anaerobic community in soil.

Diuron biotransformation and its effects on biofilm bacterial community structure.

The effect of realistic environmental contamination of diuron on natural epilithic biofilms dwelling bacterial communities and their transformation capacities were investigated by using microcosm experiments. Cobbles carrying biofilms from two sites ("Pau" and "Lacq") located in areas of contrasting pesticide use (urban and agricultural) on the Gave de Pau river (South-West France) were analysed. The water of the upstream site, Pau, was characterised by fewer pesticides than the water of Lacq, whereas concentrations were higher at Pau. The sampled cobbles were exposed to diuron (10 µg L(-1)) in microcosms. After 3 weeks of exposure, pesticides were analysed and bacterial community structures were assessed with terminal-restriction fragment length polymorphism (T-RFLP). Diuron was biotransformed during contact with biofilms, revealing that these communities contribute to the production of DCPMU (1-(3,4-dichlorophenyl)-3-methylurea) and DCPU metabolites (1-(3,4-dichlorophenyl) urea) in the river ecosystems. Bacterial communities from the most contaminated site appeared to be more resistant to diuron exposure. Correlation analyses combining chemical data with molecular fingerprinting showed that past in situ exposure drove the response of the bacterial communities.

Organogenesis and differentiation of the pancreas in the toad Bufo bufo L.

In Bufo bufo at stage III6 the first endocrine islets appear in the part of the pancreas corresponding to the dorsal anlage. At stage IV2, 5 days later, the pancreatic duct develops and new islets arise by budding off from the ductal epithelium. The ultrastructural study of the secretory granules morphology of endocrine cells has distinguished four different cell types: B-cells (stage III9), A-cells (stage IV3), D-cells (stage IV3) and a fourth type not yet identified (stage IV3). By immunocytology insulin and corticotropin-releasing factor (CRF) cells have been demonstrated at stage III9, and glucagon and somatostatin cells at stage IV1. Lastly, endocrine islets can be homogeneous (predominantly containing insulin cells, rarely glucagon cells) or heterogeneous (insulin cells at the centre and glucagon or somatostatin cells at the periphery). Hypotheses are put forward for the origin and the constitution of the different generations of endocrine islets and isolated cells.

Experimental study on the origin of pancreatic endocrine cells in the toad Bufo bufo L.

Ablation, transplantation and culture experiments were used to determine the respective roles of the pancreatic dorsal and ventral anlagen in the formation of the endocrine cells. Three successive waves of endocrine formation occur in the pancreas of Bufo bufo at three developmental stages (III6, IV1 and IV2). Each wave is derived from a different source: the first originates from the dorsal anlage, the second from the exocrine tissue of the cortex of the pancreas and the third from the pancreatic duct. Each generation of islets has a specific composition of different cell types. The first wave is only composed of insulin islets; the second wave gives rise to single insulin, glucagon and somatostatin cells; while the third wave generates single cells synthesizing one of the three hormones, homogeneous islets of insulin cells, rare glucagon islets and heterogeneous islets containing insulin cells in the centre and a few glucagon or somatostatin cells at the periphery.