Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/Organomodified Montmorillonite Nanocomposites for Potential Food Packaging Applications

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) is a versatile, biobased and biodegradable copolymer from the family of polyhydroxyalkanoates. This study aims to further ameliorate its properties in order to enhance its applicability for food packaging purposes through preparation of organomodified montmorillonite clay (OMMT) nanocomposites. Nanocomposites based on pure PHBHHx as well as commercial PHBHHx granulate, after a previous dry-mixing with OMMT in concentrations of 1, 3, 5 and 10 wt%, were prepared using melt blending and compression molding. Investigation of the samples showed well dispersed nanofiller and highly intercalated nanocomposites, resulting in a continuous decrease in gas permeability, lowering O₂, CO₂ and water vapor permeability with about 5–7 % and approximately 40 % at OMMT concentration of 1 and 10 wt%, respectively. Besides gas permeability, other properties were affected as well. Thermal stability of the samples increased gradually up to 5 wt% nanofiller, but was reduced at 10 wt%. In order to investigate the effects of OMMT and molecular weights on PHBHHx crystallization, nanocomposites were also produced by solvent-casting and compared to those obtained by melt-blending. Crystallization was retarded, because of severe lowering of molecular weight due to processing-induced chain scission, catalyzed by OMMT moisture. However, this reduction was counteracted for a large part by using commercial PHBHHx granulate, which has shown better crystallization properties. The samples were rendered increasingly more brittle, displaying higher Young’s modulus and severely reduced elongation at break. From this study it appeared that, upon viewing all affected properties as a whole, the sample based on commercial PHBHHx and containing 3 wt% OMMT shows most promise for possible applications, however further research must be performed in order to exploit their fullest potential.     

Farming and Landscape Management: How French Farmers are Coping with the Ecologization of Their Activities

In Europe, an increasing share of public subsidies for food production is being transferred towards the production of goods and environmental services. Today, farmers hesitate between the quest for technical and economic performance, which has been the paradigm of their professional activities since the 1960s, on one hand, and taking account of the environmental concerns that have been imposed since the middle of the 80s, on the other. Is it possible for farmers to continue to work according to the paradigm of the producer of agri-food goods, and how do they react to the ecologization of their activities? In this paper, we will see the difficulties and sources of tension induced by landscape maintenance in the daily professional practice of the farmers. We will see that the professional identity of the farmers is profoundly brought into question by these changes (substitution of strictly “agricultural issues” by more general concerns such as “rural issues,” substitution of the farmer by the “ecologized” peasant...). The topic of landscape reveals social strains between farmers. It also raises the question of the legitimacy of farmers to define the sense of their activities by themselves. Finally we will see that environmental orientations do not systematically open up new prospects for all farmers; they sometimes contribute to increase the inequalities between farmers (financial support proportional to land property, marginalization of farmers who are less socially integrated...).     

Utilisation of Supernatants of Pure Cultures of Streptomyces thermocarboxydus NH50 to Reduce Chromium Toxicity and Mobility in Contaminated Soils

Chromium is a heavy metal used in various industrial sectors. Improper handling and storage of chromium-laden effluents or wastes can lead to the pollution of the environment. The most toxic form is the more mobile one: hexavalent chromium Cr(VI). The reduction of Cr(VI) results in the immobilisation of chromium into its less toxic trivalent form Cr(III). This phenomenon may prevent the contamination of groundwater when the soil in the vadose zone is contaminated. Many bacteria have been isolated from contaminated soils and described to reduce Cr(VI) into Cr(III). A new Cr(VI)-reducing strain, identified as a Streptomyces thermocarboxydus,has been isolated and studied in our laboratories for its ability to reduce Cr(VI). This aerobic bacterium, in contrast to other genera described which mediate reduction via enzymes, produces reducing agents into the culture supernatants. Cr(VI) reduction by these substances is accelerated by the presence of small concentration of cupric ions (Cu²⁺). The reducing agent(s) can be easily recovered from the bacterial cultures and used as cell-free solution to treat contaminated soils by an in situ or ex situ processes.     

Natural and Artificial Functionalized Biopolyesters. II. Medium-Chain Length Polyhydroxyoctanoates from Pseudomonas Strains

Sixteen Pseudomonas strains have been tested with a view to developing medium-chain length polyhydroxyalkanoates. Four strains were selected and it is shown that their ability for producing three different polyesters with variable properties was dependent on the strains and substrates. Otherwise, Pseudomonas oleovorans was grown on a mixture of sodium octanoate and undecenoate salts at a 90/10 mol/mol ratio. The corresponding copolymer, bearing lateral double bonds, was chemically modified in the carboxy group. Finally, the ability to tailor-make functional bacterial polyesters aimed at temporary therapeutic applications is demonstrated.     

Persistence and growth of faecal culturable bacterial indicators in water column and sediments of Vidy Bay, Lake Geneva, Switzerland

The aims of this study was to investigate the persistence and the growth of culturable bacterial indicators (CBI) including total coliforms (TC) and faecal coliforms represented by Escherichia coli, enterococcus (ENT), and aerobic mesophilic bacteria (AMB) in the surface sediments and the water column of Vidy Bay (Lake Geneva, City of Lausanne, Switzerland). The study was carried out for 60 d using microcosms containing Sewage Treatment Plant (STP) e uent and nonsterile water without CBI, as well as contaminated and non-contaminated sediments. The e ects of water temperature and of organic matter associated with sediments on the survival of CBI in the sediments and the water column were observed. The number of CBI colonies in the contaminated sediments of Vidy Bay and in the STP e uent was almost identical in the order of 105–107, 104–106, 103–105, and 104–107 CFU/100 g sediment or /100 mL water for TC, E. coli, ENT, and AMB respectively. A degradation of CBI was observed in the sediments where organic mater content was low and in the water column at a temperature of 10°C after 5 d of experimentation. In addition, a growth of CBI was observed in the sediment which is rich in organic matter at 20°C. The results of this study indicate: (1) the higher concentrations of the CBI observed in di erent points in the water column of Vidy Bay may not be explained only by the recent contribution of the three potential sources of the Bay contamination including STP and the Chamberonne and Flon Rivers, but also by the persistence, removal from sediment and multiplication of CBI in the sediment and water column; (2) the sediment of Vidy Bay constitute a reservoir of CBI and can even support their growth; and (3) the CBI not only survive in sediments, but also can be remobilized and increased in the water column, therefore, it become a permanent microbiological pollution in Vidy Bay.     

Validation of a conductometric bienzyme biosensor for the detection of proteins as marker of organic matter in river samples

This article describes a conductometric bi-layer based bienzyme biosensor for the detection of proteins as a marker of organic matter in rivers. Proteins were chosen to be used as indicators of urban pollution. The working mechanism of the bienzyme biosensor is based on the enzymatic hydrolysis of proteins into several fractions (peptides and amino acids), which results in a local conductivity change depending of the concentration of proteins. In this work, we began with the optimization of biosensor response using bovine serum albumin (BSA) as standard protein. For this objective seven enzymatic biosensors were prepared: four enzymatic sensors with only one layer of enzyme (proteinase K, trypsin, pronase or protease X) and three other enzymatic sensors with two layers (first layer: membrane containing proteinase K; second layer: one of the three other enzymes: trypsin, pronase or protease X). The biosensors were obtained through the deposition of enzymatic layers and the cross-linking process between enzymes and BSA in saturated glutaraldehyde vapour. The response of the various biosensors, described previously, were compared with the values of total organic carbon (TOC), and those of organic nitrogen (Norg), as determined by the laboratory accredits (CEMAGREF of Lyon) using the traditional method of analysis (NF EN 1484, infrared spectroscopy) and (NF EN 25663, mineralization/colorimetry assay) respectively for each water sample obtained from di erent sites in Lyon (France). The linear correlations obtained with the response of the seven biosensors showed the most important indices of correlations for the biosensor with two enzymatic layers: proteinase K + pronase (pkp). The optimum conditions for the preparation of the pkp biosensor increased the sensitivity and gave a limit of quantification of 0.583 g/L for TOC and 0.218 g/L for Norg in water samples. This sensor shows good reproducibility (2.28%), a capacity to be used at temperatures range 10– 30°C (depending on the season) and moreover a long lifetime (5 weeks).     

Sensitivity of system stability to model structure

A community is stable, and resilient, if the levels of all community variables can return to the original steady state following a perturbation. The stability properties of a community depend on its structure, which is the network of direct effects (interactions) among the variables within the community. These direct effects form feedback cycles (loops) that determine community stability. Although feedback cycles have an intuitive interpretation, identifying how they form the feedback properties of a particular community can be intractable. Furthermore, determining the role that any specific direct effect plays in the stability of a system is even more daunting. Such information, however, would identify important direct effects for targeted experimental and management manipulation even in complex communities for which quantitative information is lacking. We therefore provide a method that determines the sensitivity of community stability to model structure, and identifies the relative role of particular direct effects, indirect effects, and feedback cycles in determining stability. Structural sensitivities summarize the degree to which each direct effect contributes to stabilizing feedback or destabilizing feedback or both. Structural sensitivities prove useful in identifying ecologically important feedback cycles within the community structure and for detecting direct effects that have strong, or weak, influences on community stability. The approach may guide the development of management intervention and research design. We demonstrate its value with two theoretical models and two empirical examples of different levels of complexity.     

Unexpected effects of sublethal doses of insecticide on the peripheral olfactory response and sexual behavior in a pest insect

Pesticides have long been used as the main solution to limit agricultural pests, but their widespread use resulted in chronic or diffuse environmental pollutions, development of insect resistances, and biodiversity reduction. The effects of low residual doses of these chemical products on organisms that affect both targeted species (crop pests) but also beneficial insects became a major concern, particularly because low doses of pesticides can induce unexpected positive—also called hormetic—effects on insects, leading to surges in pest population growth at greater rate than what would have been observed without pesticide application. The present study aimed to examine the effects of sublethal doses of deltamethrin, one of the most used synthetic pyrethroids, known to present a residual activity and persistence in the environment, on the peripheral olfactory system and sexual behavior of a major pest insect, the cotton leafworm Spodoptera littoralis. We highlighted here a hormetic effect of sublethal dose of deltamethrin on the male responses to sex pheromone, without any modification of their response to host-plant odorants. We also identified several antennal actors potentially involved in this hormetic effect and in the antennal detoxification or antennal stress response of/to deltamethrin exposure.     

Metal availability in a highly contaminated, dredged-sediment disposal site: Field measurements and geochemical modeling

Two complementary approaches were used to characterize arsenic and metal mobilizations from a dredged-sediment disposal site: a detailed field study combined with hydrogeochemical modeling. Contaminants in sediments were found to be mainly present as sulfides subject to oxidation. Secondary phases (carbonates, sulfates, (hydr)oxides) were also observed. Oxidative processes occurred at different rates depending on physicochemical conditions and contaminant contents in the sediment. Two distinct areas were identified on the site, each corresponding to a specific contaminant mobility behavior. In a reducing area, Fe and As were highly soluble and illustrated anoxic behavior. In well-oxygenated material, groundwater was highly contaminated in Zn, Cd and Pb. A third zone in which sediments and groundwater were less contaminated was also characterized. This study enabled us to prioritize remediation work, which should aim to limit infiltration and long-term environmental impact.     

Atmospheric phenanthrene pollution modulates carbon allocation in red clover (Trifolium pratense L.)

The influence of atmospheric phenanthrene (PHE) exposure (160 μg m⁻³) during one month on carbon allocation in clover was investigated by integrative (plant growth analysis) and instantaneous ¹³CO₂ pulse-labelling approaches. PHE exposure diminished plant growth parameters (relative growth rate and net assimilation rate) and disturbed photosynthesis (carbon assimilation rate and chlorophyll content), leading to a 25% decrease in clover biomass. The root-shoot ratio was significantly enhanced (from 0.32 to 0.44). Photosynthates were identically allocated to leaves while less allocated to stems and roots. PHE exposure had a significant overall effect on the ¹³C partitioning among clover organs as more carbon was retained in leaves at the expense of roots and stems. The findings indicate that PHE decreases root exudation or transfer to symbionts and in leaves, retains carbon in a non-structural form diverting photosynthates away from growth and respiration (emergence of an additional C loss process).