Effet du chlore sur la colonisation bactérienne d'un réseau expérimental de distribution d'eau

La contamination bactérienne de la phase eau d'un réseau de distribution résulte d'une multiplication des bactéries sur les parois des canalisations d'eau (biofilms) suivie de leur arrachage et de leur transport dans le flux circulant. Ce travail met en évidence l'effet du chlore, d'une part, sur la formation des biofilms et, d'autre part, sur des biofilms déjà constitués. Des éprouvettes de matériaux neufs introduites dans des eaux présentant des concentrations en chlore total variant de 2,4 à 0,02 mg/l et véhiculant entre 0,5 x 106 et 5 x 105 cellules bactériennes/mi (dont 1 à 10 % de bactéries cultivables) sont rapidement colonisées (106 à 108 cellules/cm2). L'effet du chlore est sensible sur les cellules totales pour des concentrations de l'ordre de 1 à 2,4 mg/l. Sur les bactéries cultivables, un ralentissement de la croissance du biofilm est observé dès 0,3 mg/1 de chlore total. Par contre, des résiduels de 0,02 ou 0,05 mg/l sont sans effet sur la cinétique de formation des biofilms. Des résiduels moyens de chlore total compris entre 2,3 et 3,4 mg/l appliqués en continu pendant 14 jours sur un biofilm constitué d'environ 8,7 x 106 cellules par cm2 (1,7 % de bactéries cultivables), entraînent l'élimination d'environ 90 % des bactéries fixées (abattement d'1 logarithme) durant les premiers jours d'exposition. L'altération du biofilm exposé à un résiduel de chlore total de l'ordre de 1,3 mg/l est identique, mais toutefois plus étalée dans le temps. Ces essais réalisés sur des éprouvettes de PVC, PE et mortier de ciment n'ont pas permis la mise en évidence de comportements différents de ces 3 supports..Bacterial accumulation in drinking water systems results both of cell deposition on the pipe walls and attached bacteria growth. The presence of a complex biofilm (cells embedded in a matrix of exopolymers) leads to a continuous contamination of the water phase resulting from the erosion of the attached growing biomass. Then, many tentatives to lmit the formation of such a biofilm have been suggested as the removal of biodegradable organic matter fram water or as the application of disinfectant. However, the efficiency of chlorination of the distribution system is debatable. Indeed, adhesion is often described as a factor of protection of attached bacteria which counterbalances the expected effect of disinfectant. Then, the aim of this experimental work is using a model distribution system to evaluate (i) the kinetics of biofilm accumulation on coupons of new materials (Polyvinyl chlorure : PVC, polyethylene : PE, cement) disposed in a constantly chlorinated system (residual total chlorine from 0.021o 2.4 mg. l-1), (ii) the effect of chlorination on previously accumulated biofilms.The industrial pilot plant used in this study is comprised of five loops serially disposed (fig. 1). From previous study of simulation, one may assume that each loop works like a perfectly mixed reactor when the whole pilot plant is equivalent to an infinite tubular reactor with high axial dispersion coefficient. During the experiment, the pilot was continuously fed with finished drinking water front the surface water treatment plant of city of Nancy (i.e. natural finished water with its own chlorine demand, organic nutrients and heterotrophic bacteria).Total number of cells (epifluorescence counts) and heterotrophic plate count bacteria (15 days of incubation at 20 °C) were enumerated both in the water and, after sonication, on the surface of the coupons of tested materials.The first experimentations show that chlorine slows clown the kinetic of deposition of bacteria onto the pipe wall but never prohibits biofilm formation. When the drinking waters carried from 2.4 to 0.02 mg.1-1 of chlorine and from 0.5 to 5 x 105 ml-1 bacterial cells, biofilm is observed after 24 hours of immersion of the coupons with at least 101 to 106 bacteria/cm2. Respectively, the deposition or/and growth rates of total cells are drastically affected only for chlorine residual as high as 1 to 2.4 mg. 1-1. The number of heterotrophic plate count of the biofilm is affected with lower chlorine residual (around 0.3 mg.1-1) but residual concentration as low as 0.05 mg.1-1 are ineffective.The tentatives carried out in the second experience on preformed biofilms (2 months old biofilms, 8.7 x 106 cells/cm2) show that the continuous application of 2.3 to 3.4 mg. 1-1 of residual chlorine for 14 days, leads to the removal of only 90 % of attached total cells without modifications of the proportion of attached alive bacteria (around 1.7 %) into the biofitm. In other wards, a highly chlorinated networks shows at minima 106 attached cells/cm2. Its generally takes several days to reply to the chlorine demand of the system and to have a quasi steady state reactor in terms of residual chlorine.These assays carried out with three types of coupons (PVC, PE, cement lined cast iron) did not show any difference between the tested materials.The limited efficiency of chlorine against the biofilm can be explained by transfert limitations within the visquous layer, high consumption of chlorine by the biopolymers of the attached matrix (proteins...) or low sensitivity to the disinfectant of the slow growing attached bacteria. Then chlorination is really not a panacea in biofilm war but has to be applied in combination with other methods as biodegradable organic matter removal, hydraulic regime improvement..

In Situ mechanical effects of a specific neurodynamic mobilization of the superficial fibular nerve: A cadaveric study

Context: A specific neurodynamic mobilization for the superficial fibular nerve (SFN) has been suggested in the reference literature for manual therapists to evaluate nerve mechanosensitivity in patients. However, no biomechanical studies examined the ability of this technique to produce nerve strain. Therefore, mechanical specificity of this technique is not yet established. Objective: The aim of our study was to test whether this examination and treatment technique was producing nerve strain in the fresh frozen cadaver and the contribution of each motion to total longitudinal strain. Design: Quantitative original research, controlled laboratory study Methods: A differential variable reluctance transducer was inserted in ten SFN from six fresh cadavers to measure strain during the mobilization. A specific sequence of plantar flexion (PF), ankle inversion (INV), straight leg raise (SLR) position and 30{degree sign} of hip adduction (ADD) was applied to the lower limb. The mobilization was repeated at 0°, 30°, 60° and 90° of Straight Leg Raise (SLR) position to measure the impact of hip flexion position. Findings: Compared to a resting position, this neurodynamic mobilization produced a significant amount of strain in the SFN (7.93% ± 0.51 P < 0.001). PF (59.34% ± 25.82) and INV (32.80% ± 21.41) accounted for the biggest proportion of total strain during the mobilization. No significant difference was reported between different hip flexion positions. Hip ADD did not significantly contribute to final strain (0.39% ± 10.42 P> 0,05) although high subject variability exists. Conclusion: Ankle motions should be considered the most important during neurodynamic assessment of the SFN for distal entrapment. These results suggest that this technique produces sufficient strain in the SFN and could therefore be evaluated In Vivo for correlation with mechanosensitivit

Degradation of YRA1 Pre-mRNA in the Cytoplasm Requires Translational Repression, Multiple Modular Intronic Elements, Edc3p, and Mex67p

The yeast YRA1 pre-mRNA contains multiple intronic elements that regulate transcript decay and translatability via the Edc3p decapping activator and the Mex67p/Mtr2p export receptor

Innate immune cell activation after HIV-1 vaccine administration is associated with increased antibody production

The RV144 Thai phase III clinical trial’s canarypox–protein HIV vaccine regimen showed modest efficacy in reducing infection. We therefore sought to determine the effects of vaccine administration on innate cell activation and subsequent associations with vaccine-induced immune responses. RV306 was a randomized, double-blind clinical trial in HIV-uninfected Thai adults that tested delayed boosting following the RV144 regimen. PBMC collected from RV306 participants prior to and 3 days after the last boost were used to investigate innate immune cell activation. Our analysis showed an increase in CD38+ mucosal associated invariant T (MAIT) cells, CD38+ invariant natural killer T (iNKT) cells, CD38+ γδ T cells, CD38+, CD69+ and HLA-DR+ NK cells 3 days after vaccine administration. An increase in CD14-CD16+ non-classical monocytes and CD14+CD16+ intermediate monocytes accompanied by a decrease in CD14+CD16- classical monocytes was also associated with vaccine administration. Inclusion of ALVAC-HIV in the boost did not further increase MAIT, iNKT, γδ T, and NK cell activation or increase the proportion of non-classical monocytes. Additionally, NK cell activation 3 days after vaccination was positively associated with antibody titers of HIV Env-specific total IgG and IgG1. Vδ1 T cell activation 3 days after vaccine administration was associated with HIV Env-specific IgG3 titers. Finally, we observed trending associations between MAIT cell activation and Env-specific IgG3 titers and between NK cell activation and TH023 pseudovirus neutralization titers. Our study identifies a potential role for innate cells, specifically NK, MAIT, and γδ T cells, in promoting antibody responses following HIV-1 vaccine administration

Revisions to the derivation of the Australian and New Zealand guidelines for toxicants in fresh and marine waters

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality are a key document in the Australian National Water Quality Management Strategy. These guidelines released in 2000 are currently being reviewed and updated. The revision is being co-ordinated by the Australian Department of Sustainability, Environment, Water, Population and Communities, while technical matters are dealt with by a series of Working Groups. The revision will be evolutionary in nature reflecting the latest scientific developments and a range of stakeholder desires. Key changes will be: increasing the types and sources of data that can be used; working collaboratively with industry to permit the use of commercial-in-confidence data; increasing the minimum data requirements; including a measure of the uncertainty of the trigger value; improving the software used to calculate trigger values; increasing the rigour of site-specific trigger values; improving the method for assessing the reliability of the trigger values; and providing guidance of measures of toxicity and toxicological endpoints that may, in the near future, be appropriate for trigger value derivation. These changes will markedly improve the number and quality of the trigger values that can be derived and will increase end-users’ ability to understand and implement the guidelines in a scientifically rigorous manner

Hunger Artists: Yeast Adapted to Carbon Limitation Show Trade-Offs under Carbon Sufficiency

As organisms adaptively evolve to a new environment, selection results in the improvement of certain traits, bringing about an increase in fitness. Trade-offs may result from this process if function in other traits is reduced in alternative environments either by the adaptive mutations themselves or by the accumulation of neutral mutations elsewhere in the genome. Though the cost of adaptation has long been a fundamental premise in evolutionary biology, the existence of and molecular basis for trade-offs in alternative environments are not well-established. Here, we show that yeast evolved under aerobic glucose limitation show surprisingly few trade-offs when cultured in other carbon-limited environments, under either aerobic or anaerobic conditions. However, while adaptive clones consistently outperform their common ancestor under carbon limiting conditions, in some cases they perform less well than their ancestor in aerobic, carbon-rich environments, indicating that trade-offs can appear when resources are non-limiting. To more deeply understand how adaptation to one condition affects performance in others, we determined steady-state transcript abundance of adaptive clones grown under diverse conditions and performed whole-genome sequencing to identify mutations that distinguish them from one another and from their common ancestor. We identified mutations in genes involved in glucose sensing, signaling, and transport, which, when considered in the context of the expression data, help explain their adaptation to carbon poor environments. However, different sets of mutations in each independently evolved clone indicate that multiple mutational paths lead to the adaptive phenotype. We conclude that yeasts that evolve high fitness under one resource-limiting condition also become more fit under other resource-limiting conditions, but may pay a fitness cost when those same resources are abundant

Phylogenetic Analysis of the Complete Mitochondrial Genome of Madurella mycetomatis Confirms Its Taxonomic Position within the Order Sordariales

Background: Madurella mycetomatis is the most common cause of human eumycetoma. The genus Madurella has been characterized by overall sterility on mycological media. Due to this sterility and the absence of other reliable morphological and ultrastructural characters, the taxonomic classification of Madurella has long been a challenge. Mitochondria are of monophyletic origin and mitochondrial genomes have been proven to be useful in phylogenetic analyses. Results: The first complete mitochondrial DNA genome of a mycetoma-causative agent was sequenced using 454 sequencing. The mitochondrial genome of M. mycetomatis is a circular DNA molecule with a size of 45,590 bp, encoding for the small and the large subunit rRNAs, 27 tRNAs, 11 genes encoding subunits of respiratory chain complexes, 2 ATP synthase subunits, 5 hypothetical proteins, 6 intronic proteins including the ribosomal protein rps3. In phylogenetic analyses using amino acid sequences of the proteins involved in respiratory chain complexes and the 2 ATP synthases it appeared that M. mycetomatis clustered together with members of the order Sordariales and that it was most closely related to Chaetomium thermophilum. Analyses of the gene order showed that within the order Sordariales a similar gene order is found. Furthermore also the tRNA order seemed mostly conserved. Conclusion: Phylogenetic analyses of fungal mitochondrial genomes confirmed that M. mycetomatis belongs to the order of Sordariales and that it was most closely related to Chaetomium thermophilum, with which it also shared a comparable gene and tRNA order

The Properties of Adaptive Walks in Evolving Populations of Fungus

A novel method to infer the number and fitness effect of beneficial mutations reveals that the bulk of adaptive evolution is attributable to a few mutations with variable effects on fitness

Probing Microsecond Time Scale Dynamics in Proteins by Methyl 1H Carr−Purcell−Meiboom−Gill Relaxation Dispersion NMR Measurements. Application to Activation of the Signaling Protein NtrCr

To study microsecond processes by relaxation dispersion NMR spectroscopy, low power deposition and short pulses are crucial and encourage the development of experiments that employ H-1 Carr-Purcell-Meiboom-Gill (CPMG) pulse trains. Herein, a method is described for the comprehensive study of microsecond to millisecond time scale dynamics of methyl groups in proteins, exploiting their high abundance and favorable relaxation properties. In our approach, protein samples are produced using [H-1, C-13]-D-glucose in similar to 100% D2O, which yields CHD2 methyl groups for alanine, valine, threonine, isoleucine, leucine, and methionine residues with high abundance, in an otherwise largely deuterated background. Methyl groups in such samples can be sequence-specifically assigned to near completion, using C-13 TOCSY NMR spectroscopy, as was recently demonstrated (Often, R.; et al. J. Am. Chem. Soc. 2010, 132, 2952-2960). In this Article, NMR pulse schemes are presented to measure H-1 CPMG relaxation dispersion profiles for CHD2 methyl groups, in a vein similar to that of backbone relaxation experiments. Because of the high deuteration level of methyl-bearing side chains, artifacts arising from proton scalar coupling during the CPMG pulse train are negligible, with the exception of Ile-delta 1 and Thr-gamma 2 methyl groups, and a pulse scheme is described to remove the artifacts for those residues. Strong C-13 scalar coupling effects, observed for several leucine residues, are removed by alternative biochemical and NMR approaches. The methodology is applied to the transcriptional activator NtrC(r), for which an inactive/active state transition was previously measured and the motions in the microsecond time range were estimated through a combination of backbone N-15 CPMG dispersion NMR spectroscopy and a collection of experiments to determine the exchange-free component to the transverse relaxation rate. Exchange contributions to the H-1 line width were detected for 21 methyl groups, and these probes were found to collectively report on a local structural rearrangement around the phosphorylation site, with a rate constant of (15.5 +/- 0.5) x 10(3) per second (i.e., tau(ex) = 64.7 +/- 1.9 mu s). The affected methyl groups indicate that, already before phosphorylation, a substantial, transient rearrangement takes place between helices 3 and 4 and strands 4 and 5. This conformational equilibrium allows the protein to gain access to the active, signaling state in the absence of covalent modification through a shift in a pre-existing dynamic equilibrium. Moreover, the conformational switching maps exactly to the regions that differ between the solution NMR structures of the fully inactive and active states. These results demonstrate that a cost-effective and quantitative study of protein methyl group dynamics by H-1 CPMG relaxation dispersion NMR spectroscopy is possible and can be applied to study functional motions on the microsecond time scale that cannot be accessed by backbone N-15 relaxation dispersion NMR. The use of methyl groups as dynamics probes extends such applications also to larger proteins