Can quarantine plant-parasitic nematodes within wastes be managed by useful tools in a circular economy approach?

Seen as an integral part of sustainable development, circular economy represents a model of production and consumption notably based on the limitation of both resource wastage and environmental impact. Laboratories and commercial companies working on plant pathogens, in particular quarantine species, must effectively disinfect their waste to avoid disseminating these organisms. The methods used for waste disinfection can however incur high energy costs or pose environmental and human health hazards. Here, we tested the effectiveness of five disinfection methods - chlorination, heat treatment, composting, mesophilic methanation and waste stabilization ponds - on plant-parasitic nematodes belonging to the genera Globodera and Meloidogyne. For the widely used chlorination and heat treatment methods, we showed that they can be very effective in inactivating nematodes at relatively low chlorine doses and temperatures (60 °C-3 min and 50 °C-30 min), respectively. For the three other disinfection methods tested, initially designed for waste recycling, we obtained different levels of efficiency. Composting and mesophilic methanation (based on cattle or pig slurry) both led to the complete elimination of nematodes, even for short treatment durations. However, waste stabilization ponds showed contrasting results, ranging from virtually no effect to high levels of inactivation of nematodes. Our study demonstrates that it is possible to use more environmentally friendly disinfection methods to control plant-parasitic nematodes. In particular, this finding paves the way towards the treatment of infected plant materials using composting or methanation, providing that disinfection is still reached under other (real-life) treatment conditions, especially with other kinds of waste. Both composting and methanation recycle and thus valorize infected waste; they are viable alternatives to landfilling or incineration, thereby demonstrating the usefulness of a circular economy approach.

A Novel In Vitro Tool to Study Cyst Nematode Chemotaxis.

This study presents a novel three-dimensional (3D) tool "3D in vitro choice" for chemotaxis assays with cyst nematodes. The original 3D in vitro choice was customized through digital printing. Freshly hatched second stage juveniles (J2s) of the cyst nematode Globodera pallida were used as the nematode model to illustrate chemo-orientation behavior in the 3D system. The efficiency and reliability of the 3D in vitro choice were validated with 2% Phytagel as navigation medium, in three biological assays and using tomato root exudates or potato root border cells and their associated mucilage as a positive attractant as compared with water. For each biological assay, J2s were hatched from the same population of a single generation glasshouse-cultured cysts. This novel easy to use and low-cost 3d-device could be a useful replacement to Petri dishes assays in nematode behavioral studies due to the ease of deposition of nematodes and test substances, coupled with its distinctive zones that allow for precision in choice making by the nematodes.

Hatching Induction of Cyst Nematodes in Bare Soils Drenched With Root Exudates Under Controlled Conditions.

Cyst nematodes account for substantial annual yield losses in crop production worldwide. Concerns over environmental and health issues due to the use of chemical nematicides mean alternative sustainable and integrated solutions are urgently required. Hatch induction of encysted eggs in the absence of host plants, i.e., 'suicide-hatching,' could be a sustainable alternative in reducing population densities of cyst nematodes in infested soils. Here we examined in situ hatching of encysted eggs of Globodera pallida, Heterodera carotae, and Heterodera schachtii at varying soil depths, following exogenous applications of host root exudates in repeated glasshouse experiments. Cysts were retrieved 30 or 43 days post-incubation depending on the nematode species and assessed for hatching rates relative to the initial number of viable eggs per cyst. Hatching of the potato cyst nematode G. pallida depended on both soil moisture and effective exposure to root exudates, and to a lesser extent on exudate concentration. The carrot cyst nematode H. carotae had over 75% hatched induced by root exudate irrespective of the concentration, with better hatch induction at 20 cm as compared with 10 cm soil depth. Hatching of the beet cyst nematode H. schachtii largely depended on the soil moisture level at constant temperature, rather than the type or concentration of root exudates applied. As a conclusion, exogenously applied host root exudates may play a major role in inducing in situ hatch of encysted eggs of potato and carrot cyst nematodes in the absence of host plant under favorable soil temperature/moisture conditions. To improve such strategy, the characterization of chemical profiles of the root exudate composition and field validation are currently ongoing.

Efficient hydrolytic cleavage of plasmid DNA by chloro-cobalt(II) complexes based on sterically hindered pyridyl tripod tetraamine ligands: synthesis, crystal structure and DNA cleavage.

Four new cobalt(ii) complexes [Co(6-MeTPA)Cl]ClO4/PF6 (2/2a), [Co(6-Me2TPA)Cl]ClO4/PF6 (3/3a), [Co(BPQA)Cl]ClO4/PF6 (4/4a) and [Co(BQPA)Cl]ClO4/PF6 (5/5a) as well as [Co(TPA)Cl]ClO4 (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me2TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a-5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH3CN-H2O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H2O)](2+). The pKa values of the coordinated H2O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1-5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis-Menten kinetic conditions, the catalytic rate constants, kcat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the kcat value for complex 4 (6.02 h(-1)), where [Co(BPQA)(H2O)](2+) is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN3) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the kcat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)](+). The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(ii) center.

Transcriptional effects of glucocorticoid receptors in the dentate gyrus increase anxiety-related behaviors.

The Glucocorticoid Receptor (GR) is a transcription factor ubiquitously expressed in the brain. Activation of brain GRs by high levels of glucocorticoid (GC) hormones modifies a large variety of physiological and pathological-related behaviors. Unfortunately the specific cellular targets of GR-mediated behavioral effects of GC are still largely unknown. To address this issue, we generated a mutated form of the GR called DeltaGR. DeltaGR is a constitutively transcriptionally active form of the GR that is localized in the nuclei and activates transcription without binding to glucocorticoids. Using the tetracycline-regulated system (Tet-OFF), we developed an inducible transgenic approach that allows the expression of the DeltaGR in specific brain areas. We focused our study on a mouse line that expressed DeltaGR almost selectively in the glutamatergic neurons of the dentate gyrus (DG) of the hippocampus. This restricted expression of the DeltaGR increased anxiety-related behaviors without affecting other behaviors that could indirectly influence performance in anxiety-related tests. This behavioral phenotype was also associated with an up-regulation of the MAPK signaling pathway and Egr-1 protein in the DG. These findings identify glutamatergic neurons in the DG as one of the cellular substrate of stress-related pathologies.