Dual role of the antioxidant enzyme peroxiredoxin 6 in skin carcinogenesis.

The antioxidant enzyme peroxiredoxin 6 (Prdx6) is a key regulator of the cellular redox balance, particularly under stress conditions. We identified Prdx6 as an important player in different phases of skin carcinogenesis. Loss of Prdx6 in mice enhanced the susceptibility to skin tumorigenesis, whereas overexpression of Prdx6 in keratinocytes of transgenic mice had the opposite effect. The tumor-preventive effect of Prdx6, which was observed in a human papilloma virus 8-induced and a chemically induced tumor model, was not due to alterations in keratinocyte proliferation, apoptosis, or in the inflammatory response. Rather, endogenous and overexpressed Prdx6 reduced oxidative stress as reflected by the lower levels of oxidized phospholipids in the protumorigenic skin of Prdx6 transgenic mice and the higher levels in Prdx6-knockout mice than in control animals. In contrast to its beneficial effect in tumor prevention, overexpression of Prdx6 led to an acceleration of malignant progression of existing tumors, revealing a dual function of this enzyme in the pathogenesis of skin cancer. Finally, we found strong expression of PRDX6 in keratinocytes of normal human skin and in the tumor cells of squamous cell carcinomas, indicating a role of Prdx6 in human skin carcinogenesis. Taken together, our data point to the potential usefulness of Prdx6 activators or inhibitors for controlling different stages of skin carcinogenesis.

The peroxiredoxin Tpx1 is essential as a H202-scavenger during aerobic growth in fission yeast

Peroxiredoxins are known to interact with hydrogen peroxide (H2O2) and to participate in oxidant scavenging, redox signal transduction, and heat-shock responses. The two-cysteine peroxiredoxin Tpx1 of Schizosaccharomyces pombe has been characterized as the H2O2 sensor that transduces the redox signal to the transcription factor Pap1. Here, we show that Tpx1 is essential for aerobic, but not anaerobic, growth. We demonstrate that Tpx1 has an exquisite sensitivity for its substrate, which explains its participation in maintaining low steady-state levels of H2O2. We also show in vitro and in vivo that inactivation of Tpx1 by oxidation of its catalytic cysteine to a sulfinic acid is always preceded by a sulfinic acid form in a covalently linked dimer, which may be important for understanding the kinetics of Tpx1 inactivation. Furthermore, we provide evidence that a strain expressing Tpx1.C169S, lacking the resolving cysteine, can sustain aerobic growth, and we show that small reductants can modulate the activity of the mutant protein in vitro, probably by supplying a thiol group to substitute for cysteine 169.

Bridging the Faraoni and Selli oceanic anoxic events: late Hauterivian to early Aptian dysaerobic to anaerobic phases in the Tethys

A detailed geochemical analysis was performed on the upper part of the Maiolica Formation in the Breggia (southern Switzerland) and Capriolo sections (northern Italy). The analysed sediments consist of well-bedded, partly siliceous, pelagic carbonate, which lodges numerous thin, dark and organic-rich layers. Stable-isotope, phosphorus, organic-carbon and a suite of redox-sensitive trace-element contents (RSTE: Mo, U, Co, V and As) were measured. The RSTE pattern and C-org:P-tot ratios indicate that most organic-rich layers were deposited under dysaerobic rather than anaerobic conditions and that latter conditions were likely restricted to short intervals in the latest Hauterivian, the early Barremian and the pre-Selli early Aptian. Correlations are both possible with organic-rich intervals in central Italy (the Gorgo a Cerbara section) and the Boreal Lower Saxony Basin, as well as with the facies and drowning pattern in the Helvetic segment of the northern Tethyan carbonate platform. Our data and correlations suggest that the latest Hauterivian witnessed the progressive installation of dysaerobic conditions in the Tethys, which went along with the onset in sediment condensation, phosphogenesis and platform drowning on the northern Tethyan margin, and which culminated in the Faraoni anoxic episode. This episode is followed by further episodes of dysaerobic conditions in the Tethys and the Lower Saxony Basin, which became more frequent and progressively stronger in the late early Barremian. Platform drowning persisted and did not halt before the latest early Barremian. The late Barremian witnessed diminishing frequencies and intensities in dysaerobic conditions, which went along with the progressive installation of the Urgonian carbonate platform. Near the Barremian-Aptian boundary, the increasing density in dysaerobic episodes in the Tethyan and Lower Saxony Basins is paralleled by a change towards heterozoan carbonate production on the northern Tethyan shelf. The following return to more oxygenated conditions is correlated with the second phase of Urgonian platform growth and the period immediately preceding and corresponding to the Selli anoxic episode is characterised by renewed platform drowning and the change to heterozoan carbonate production. Changes towards more humid climate conditions were the likely cause for the repetitive installation of dys- to anaerobic conditions in the Tethyan and Boreal basins and the accompanying changes in the evolution of the carbonate platform towards heterozoan carbonate-producing ecosystems and platform drowning.

Behavioral phenotyping of glutathione-deficient mice: Relevance to schizophrenia and bipolar disorder.

Redox-dysregulation represents a common pathogenic mechanism in schizophrenia (SZ) and bipolar disorder (BP). It may in part arise from a genetically compromised synthesis of glutathione (GSH), the major cellular antioxidant and redox-regulator. Allelic variants of the genes coding for the rate-limiting GSH synthesizing enzyme glutamate-cysteine-ligase modifier (GCLM) and/or catalytic (GCLC) subunit have been associated with SZ and BP. Using mice knockout (KO) for GCLM we have previously shown that impaired GSH synthesis is associated with morphological, functional and neurochemical anomalies similar to those in patients. Here we asked whether GSH deficit is also associated with SZ- and BP-relevant behavioral and cognitive anomalies. Accordingly, we subjected young adult GCLM-wildtype (WT), heterozygous and KO males to a battery of standard tests. Compared to WT, GCLM-KO mice displayed hyperlocomotion in the open field and forced swim test but normal activity in the home cage, suggesting that hyperlocomotion was selective to environmental novelty and mildly stressful situations. While spatial working memory and latent inhibition remained unaffected, KO mice showed a potentiated hyperlocomotor response to an acute amphetamine injection, impaired sensorymotor gating in the form of prepulse inhibition and altered social behavior compared to WT. These anomalies resemble important aspects of both SZ and the manic component of BP. As such our data support the notion that redox-dysregulation due to GSH deficit is implicated in both disorders. Moreover, our data propose the GCLM-KO mouse as a valuable model to study the behavioral and cognitive consequences of redox dysregulation in the context of psychiatric disease.

Estudo da Energia da Banda de Condução em Células Solares Sensibilizadas por Complexos de Ruténio

Um dos grandes desafios do nosso tempo é o aproveitamento da energia solar e outras fontes de energias renováveis para promover um desenvolvimento sustentável em grande escala. Para além da inocuidade face ao meio ambiente, a eficiência e os reduzidos custos de produção das células solares sensibilizadas por corante (DSSC, do inglês dye-sensitized solar cells) continuam a atrair considerável interesse tanto académico como comercial. Em 1991, Grätzel e O’Regan deram um enorme avanço no desenvolvimento das DSSC, utilizando um material de eléctrodo com elevada área superficial, filmes semicondutores nanocristalinos de TiO2 com espessura na ordem dos mícrons Nas células fotovoltaicas o corante sensibilizador (S) adsorvido na camada de TiO2 vai absorver a radiação solar e transfere o electrão fotoexcitado para o semicondutor (SC), formando um par de cargas separadas. O sensibilizador oxidado é regenerado pelo mediador redox existente na solução de electrólito. Uma vez efectuado o trabalho através do circuito externo, o electrão volta para o contra eléctrodo onde reduz o dador de electrão oxidado, completando o ciclo. Desta maneira, a luz é convertida em electricidade sem transformação química permanente

Dispersion of natural arsenic in the Malcantone watershed, Southern Switzerland: field evidence for repeated sorption-desorption and oxidation-reduction processes

In recent years, elevated arsenic concentrations have been found in waters and soils of many, countries, often resulting in a health threat for the local population. Switzerland is not an exception and this paper deals with the release and subsequent fate of arsenic in a 200-km(2) mountainous watershed, characterized by crystalline silicate rocks (gneisses, schists, amphibolites) that contain abundant As-bearing sulfide ore deposits, some of which have been mined for iron and gold in the past. Using analytical methods common for mineralogical, ground water and soil studies (XRD, XRF, XAS-XANES and -EXAFS, electron microprobe, extraction, ICP, AAS with hydride generator, ion chromatography), seven different field situations and related dispersion processes of natural arsenic have been studied: (1) release by rock weathering, (2) transport and deposition by water and ice; (3) release of As to the ground and surface water due to increasing pH; (4) accumulation in humic soil horizons; (5) remobilization by reduction in water-saturated soils and stagnant ground waters; (6) remobilization by using P-rich fertilizers or dung and (7) oxidation, precipitation and dilution in surface waters. Comparison of the results with experimental adsorption studies and speciation diagrams from the literature allows us to reconstruct and identify the typical behavior of arsenic in a natural environment under temperate climatic conditions. The main parameters identified are: (a) once liberated from the primary minerals, sorption processes on Fe-oxy-hydroxides dominate over Al-phases, such as Al-hydroxides or clay minerals and limit the As concentrations in the spring and well waters between 20 and 300 mug/l. (b) Precipitation as secondary minerals is limited to the weathering domain, where the As concentrations are still high and not yet too diluted by rain and soils waters. (c) Although neutral and alkaline pH conditions clearly increase the mobility of As, the main factor to mobilize As is a low redox potential (Eh close or below 0 mV), which favors the dissolution of the Fe-oxy-hydroxides on which the As is sorbed. (d) X-ray absorption spectroscopy (XAS) of As in water-logged humic forest soils indicates that the reduction to As III only occurs at the solid-water interface and that the solid contains As as As V (e) A and Bh horizons of humic cambisols can effectively capture As when As-rich waters flow through them. Complex spatial and temporal variation of the various parameters in a watershed results in repeated mobilization and immobilization of As, which continuously transports As from the upper to the lower part of a watershed and ultimately to the ocean. (C) 2004 Elsevier B.V. All rights reserved.

7

Evidence of altered antioxidant systems and signs of elevated oxidative stress are reported in peripheral tissue and brain of schizophrenic patients, including low levels of glutathione (GSH), a major thiol antioxidant and redox buffer. Functional and genetic data indicate that an impaired regulation of GSH synthesis is a vulnerability factor for the disease. Impaired GSH synthesis from a genetic origin combined with environmental risk factors generating oxidative stress (e.g., malnutrition, exposure to toxins, maternai infection and diabetes, obstetrical complications, and psychological stress) could lead to redox dysregulation. This could subsequently perturb normal brain development and maturation with delayed functional consequences emerging in early adulthood. Depending on the nature and the time of occurrence of the environmental insults, the structural and functional delayed consequences could vary, giving rise to various endophenotypes. The use of animal models of GSH deficit represents a valuable approach to investigate how interactions between genetic and environmental factors lead to the emergence of pathologies found in the disease. Moreover, these models of GSH can be useful to investigate links between schizophrenia and comorbid somatic disorders, as dysregulation of the GSH system and elevated oxidative stress are also found in cardiovascular diseases and diabetes. This chapter reviews pharmacological and genetic rodent models of GSH synthesis dysregulation used to address some of the aforementioned issues. Up to date, these models revealed that GSH deficits lead to morphological, physiological, and behavioral alterations that are quite analogous to pathologies observed in patients. This includes hypofunction of NMDA receptors, alteration of dopamine neurotransmission, anomalies in parvalbumin-immunoreactive fast-spiking interneurons, and reduced myelination. In addition, a GSH deficit affects the brain in a region-specific manner, the anterior cingulate cortex and the ventral hippocampus being the most vulnerable regions investigated. Interestingly, a GSH deficit during a limited period of postnatal development is sufficient to have long-lasting consequences on the integrity of PV-IR interneurons in the anterior cingulate cortex and impairs cognitive functions in adulthood. Finally, these animal models of GSH deficit display behavioral impairments that could be related to schizophrenia. Altogether, current data strongly support a contributing role of a redox dysregulation on the development of pathologies associated with the illness and demonstrate the usefulness of these models to better understand the biological mechanisms leading to schizophrenia.

Stable isotope and trace element stratigraphy across the Permian-Triassic transition: A redefinition of the boundary in the Velebit Mountain, Croatia

Stable isotopes of carbonates (delta(13)C(carb), delta(18)O(carb)), organic matter (delta(13)C(org), delta(15)N(org)) and major, trace and rare earth element (REE) compositions of marine carbonate rocks of Late Permian to Early Triassic age were used to establish the position of the Permian-Triassic boundary (PTB) at two continuous sections in the Velebit Mountain, Croatia. The chosen sections - Rizvanusa and Brezimenjaca - are composed of two lithostratigraphic units, the Upper Permian Transitional Dolomite and the overlying Sandy Dolomite. The contact between these units, characterized by the erosional features and sudden occurrence of ooids and siliciclastic grains, was previously considered as the chronostratigraphic PTB. The Sandy Dolomite is characterized by high content of non-carbonate material (up to similar to 30 wt.% insoluble residue), originated from erosion of the uplifted hinterland. A relatively rich assemblage of Permian fossils (including Geinitzina, Globivalvulina, Hemigordius, bioclasts of gastropods, ostracods and brachiopods) was found for the first time in Sandy Dolomite, 5 m above the lithologic boundary in the Rizvanusa section. A rather abrupt negative delta(13)C(carb) excursion in both sections appears in rocks showing no recognizable facies change within the Sandy Dolomite, -2 parts per thousand at Rizvanusa and -1.2 parts per thousand at Brezimenjaca, 11 m and 0.2 m above the lithologic contact, respectively. This level within the lower part of the Sandy Dolomite is proposed as the chemostratigraphic PTB. In the Rizvanusa section, the delta(13)C(org) values decline gradually from similar to-25 parts per thousand in the Upper Permian to similar to-29 parts per thousand in the Lower Triassic. The first negative delta(13)C(org) excursion occurs above the lithologic contact, within the uppermost Permian deposits, and appears to be related to the input of terrigenous material. The release of isotopically light microbial soil-biomass into the shallow-marine water may explain this sudden decrease of delta(13)C(org) values below the PTB. This would support the hypothesis that in the western Tethyan realm the land extinction, triggering a sudden drop of woody vegetation and related land erosion, preceded the marine extinction. The relatively low delta(15)N(org) values at the Permian-Triassic (P-Tr) transition level, close to approximate to 0 parts per thousand, and a secondary negative delta(13)C(org) excursion of -0.5 parts per thousand point to significant terrestrial input and primary contribution of cyanobacteria. The profiles of the concentrations of redox-sensitive elements (Ce, Mn, Fe, V), biogenic or biogenic-scavenged elements (P, Ba, Zn, V), Ce/Ce* values, and normalized trace elements, including Ba/Al, Ba/Fe, Ti/Al, Al/(Al + Fe + Mn) and Mn/Ti show clear excursions at the Transitional Dolomite-Sandy Dolomite lithologic boundary and the chemostratigraphic P-Tr boundary. The stratigraphic variations indicate a major regression phase marking the lithologic boundary, transgressive phases in the latest Permian and a gradual change into shallow/stagnant anoxic marine environment towards the P-Tr boundary level and during the earliest Triassic. (C) 2010 Elsevier B.V. All rights reserved.

Biosphere/lithosphere interface : microbially-mediated CaCO3 precipitation in hypersaline and freshwater environments

Abstract: Microbial mats very efficiently cycle elements, such as C, 0, N, S and H, which makes them key players of redox processes at the biosphere-lithosphere interface. They are characterized by high metabolic activities and high turnover rates (production and consumption) of biomass, which mainly consists of cell material and of extracellular organic matter (EOM). The EOM forms a matrix, embedding the microbial cells and fulfilling various functions within the microbial mat, including: mat attachment to surfaces; creation of micro-domains within the mat; physical stabilization under hy- drodynamic stress and the protection of the cells in multiple other stress conditions. EOM mainly consists of polysaccharides, amino acids, and a variety of chemical func-tional groups {e.g., -C00H, - SH -OH). These groups strongly bind cations such as Ca2+ and Mg2+ and thus exert a strong control on carbonate mineral formation within the microbial mat. A feedback mechanism between community metabolisms, their prod¬ucts, and the surrounding physicochemical microenvironment thus influences the de¬gree of carbonate saturation favoring either carbonate precipitation or dissolution. We investigated the driving forces and mechanisms of microbialite formation in the Sari ne River, FR, Switzerland, the hypersaline lake, Big Pond, Bahamas and in labo¬ratory experiments. The two fundamentally different natural systems allowed us to compare the geochemical conditions and microbial metabolisms, necessary for car¬bonate formation in microbial mats. Although carbonates are oversaturated in both environments, precipitation does not occur on physicochemical substrates (i.e. out¬side the microbial mats). In the Sarine a high crystal nucleation threshold exceeds the carbonate saturation, despite the high carbonate alkalinity in the water column. Cyanobacterial photosynthesis strongly locally enhances the carbonate alkalinity, whereas the EOM attract and immobilize calcium, which increases the saturation state and finally leads to carbonate precipitation within the EOM (in this case the cyanobacterial sheath) as nucleation template. In Big Pond, the presence of calcium- chelating anions (i.e. sulfate) and EOM, as well as the presence of magnesium, lowers the calcium activity in the water column and mat, and thus inhibits carbonate pre¬cipitation. Coupled with other heterotrophic metabolisms, sulfate reduction uses the EOM as carbon source, degrading it. The resulting EOM consumption creates alkalin¬ity, releases calcium and consumes sulfate in mat-micro domains, which leads to the formation of carbonate layers at the top of the microbial mat. Résumé: Interface biosphère/lithosphère: médiation microbienne de la précipitation de CaC03 dans des environnements en eaux douces et hypersalines Les tapis microbiens engendrent une circulation très efficace des éléments, tels que C, 0, N, S et H, ce qui en fait des acteurs clé pour les processus d'oxydoréduction à l'inter¬face biosphère-lithosphère. Ils sont caractérisés par des taux élevés d'activité méta¬bolique, ainsi que par la production et la consommation de biomasse, principalement constituée de cellules microbiennes et de matière organique extracellulaire (MOE). Dans un tapis microbien, les cellules microbiennes sont enveloppées par une matrice de MOE qui a différentes fonctions dont l'attachement du tapis aux surfaces, la créa¬tion de micro-domaines dans le tapis, la stabilisation physique en situation de stress hydrodynamique, et la protection des cellules dans de multiples autres conditions de stress. La MOE se compose principalement de polysaccharides, d'acides aminés, et d'une variété de groupes fonctionnels chimiques (par exemple, COOH, -SH et -OH). Ces groupes se lient fortement aux cations, tels que Ca2+ et Mg2+, et exercent ainsi un contrôle fort sur la formation de CaC03 dans le tapis microbien. Un mécanisme de rétroaction, entre les métabolismes de la communauté microbienne, leurs produits, et le microenvironnement physico-chimique, influence le degré de saturation de car¬bonate, favorisant soit leur précipitation, soit leur dissolution. Nous avons étudié le moteur et les mécanismes de minéralisation dans des tapis de la Sarine, FR, Suisse et du lac hypersalin, Big Pond, aux Bahamas, ainsi que durant des expériences en laboratoire. Les deux systèmes naturels, fondamentalement dif¬férents, nous ont permis de comparer les conditions géochimiques et les métabolis¬mes nécessaires à la formation des carbonates dans des tapis microbiens. Bien que les carbonates soient sursaturés dans les deux environnements, la précipitation ne se produit pas sur des substrats physico-chimiques (en dehors du tapis microbien). Dans la Sarine, malgré un taux d'alcalinité élevé, les valeurs de seuil pour la nucléa- tion de carbonates sont plus hautes que la saturation du carbonate. La photosynthèse cyanobactérienne augmente localement l'alcalinité, alors que la MOE attire et immo¬bilise le calcium, ce qui augmente l'état de saturation et conduit finalement à la pré¬cipitation des carbonates, en utilisant la MOE comme substrat de nucléation. À Big Pond, la présence de chélateurs de calcium, notamment les anions (p.ex. le sulfate) et la MOE, ainsi que la présence de magnésium, réduit l'activité du calcium et inhibe en conséquence la précipitation des carbonates. Couplée avec d'autres métabolismes hétérotrophes, la réduction des sulfates utilise la MOE comme source de carbone, en la dégradant. Cette consommation de MOE crée l'alcalinité, consomme des sulfates et libère du calcium dans des micro-domaines, conduisant à la formation de couches de carbonates dans le haut du tapis microbien.

A glutathione precursor, N-acetyl-cysteine, modulates mismatch negativity generation in schizophrenia patients

Schizophrenia patients exhibit deficits in low-level processing, including pitch discrimination. This deficiency manifests in auditory evoked potentials (AEPs) as an impaired mismatch negativity (MMN), an electrophysiological response to infrequent target stimuli interspersed among frequent standard stimuli that typically peaks ~100ms post-stimulus onset. NMDA receptor antagonists have been shown to block MMN generation in both animals and humans, and NMDA dysfunction has been linked to the underlying pathophysiology of schizophrenia. A parallel line of evidence indicates that glutathione (GSH) regulation is perturbed in schizophrenia patients at the gene, protein and functional levels (Tosic et al., 2006). This GSH dysregulation leads to NMDA receptors' hypofunction through interaction with their redox site (Steullet et al., 2006). The present study aimed to modulate GSH levels in schizophrenia patients and assessed the effects of such a modulation on MMN generation mechanisms. N-acetyl-cysteine (NAC), a GSH precursor, was administered to schizophrenia patients, using a double-blind cross-over protocol. One group received NAC (2g/day) for 60 days and then placebo for another 60 days, and vice-versa for the second group. AEPs from patients were recorded at the onset of the protocol, at the point of cross-over, and at the end of the study. Participants were instructed to manually respond to target stimuli (2kHz pure tones occurring 20% of the time among 1kHz pure tones). Analyses of AEPs recorded at protocol onset indicated that patients (n=11) were significantly impaired in generating the MMN relative to age-matched controls (n=11). Specifically, the global field power (GFP), an index of AEP magnitude, was measured over the 70- 155ms post-stimulus interval and submitted to an analysis of variance (ANOVA). There was a significant interaction between population and stimulus frequency, indicating impaired MMN generation in patients at protocol onset. Analyses of AEPs recorded during administration of NAC (n=7) versus placebo (n=7) revealed the efficacy of this GSH precursor in modulating MMN generation mechanisms. ANOVA of GFP over the 70- 155ms post-stimulus interval, using stimulus frequency and treatment as within-participants variables, revealed a significant interaction and indicated that NAC can ameliorate MMN generation. We discuss these results in terms of potential therapeutic strategies for schizophrenia.

Características geoquímicas de sedimentos del perfil Callao, Octubre 2008

Se determinó la tendencia y variabilidad vertical de las características geoquímicas de los sedimentos y del agua intersticial en los primeros 10 cm superficiales de dos testigos de Callao, colectados en dos estaciones del perfil Callao, durante el Crucero Miniox BIC Olaya 0810: (1) E-2, a 8 mn de la costa y 98 m de profundidad, donde la materia orgánica presentó un amplio rango de variabilidad (4,75% a 56,34%) y una tendencia al incremento con la profundización del perfil vertical, al existir condiciones geoquímicas que favorecen una mayor preservación de la materia orgánica y una lenta remineralización; y (2) E-5, a 30 mn de la costa y 178 m de profundidad, donde la materia orgánica presentó una distribución más homogénea en el perfil vertical (30,72% a 36,17%). Las elevadas correlaciones (r > 0,7) de la materia orgánica total con el carbono orgánico total, así como con los fosfatos y los silicatos en sedimentos superficiales indican que la materia orgánica gobierna parcialmente las concentraciones de carbono y fósforo. La variabilidad en la conducta de distribución de las concentraciones de metales Redox sensitivos en los sedimentos recientes, está asociada a condiciones anóxicas y a la intensa actividad sulfato reductora característica en la zona de estudio.

Persistence and cell culturability of biocontrol strain Pseudomonas fluorescens CHA0 under plough pan conditions in soil and influence of the anaerobic regulator gene anr.

Certain fluorescent pseudomonads can protect plants from soil-borne pathogens, and it is important to understand how these biocontrol agents survive in soil. The persistence of the biocontrol strain Pseudomonas fluorescens CHA0-Rif under plough pan conditions was assessed in non-sterile soil microcosms by counting total cells (immunofluorescence microscopy), intact cells (BacLight membrane permeability test), viable cells (Kogure's substrate-responsiveness test) and culturable cells (colony counts on selective plates) of the inoculant. Viable but non-culturable cells of CHA0-Rif (106 cells g-1 soil) were found in flooded microcosms amended with fermentable organic matter, in which the soil redox potential was low (plough pan conditions), in agreement with previous observations of plough pan samples from a field inoculated with CHA0-Rif. However, viable but non-culturable cells were not found in unamended flooded, amended unflooded or unamended unflooded (i.e. control) microcosms, suggesting that such cells resulted from exposure of CHA0-Rif to a combination of low redox potential and oxygen limitation in soil. CHA0-Rif is strictly aerobic. Its anaerobic regulator ANR is activated by low oxygen concentrations and it controls production of the biocontrol metabolite hydrogen cyanide under microaerophilic conditions. Under plough pan conditions, an anr-deficient mutant of CHA0-Rif and its complemented derivative displayed the same persistence pattern as CHA0-Rif, indicating that anr was not implicated in the formation of viable but non-culturable cells of this strain at the plough pan.

Gènes, environnement et neurodéveloppement: te cas de la schizophrénie [Schizophrenia: genes, environment and neurodevelopment].

Psychoses are complex diseases resulting from the interaction between genetic vulnerability factors and various environmental risk factors during the brain development and leading to the emergence of the clinical phenotype at the end of adolescence. Among the mechanisms involved, a redox imbalance plays an important role, inducing oxidative stress damaging to developing neurons. As a consequence, the excitatory/inhibitory balance in cortex and the pathways connecting brain areas are both impaired. Childhood and adolescence appear as critical periods of vulnerability for deleterious environmental insults. Antioxidants, applied during the environmental impacts, should allow preventing these impairments as well as their clinical consequences.

Caracterização de concreções ferro-manganosas de solos de calcário no norte do estado de Minas Gerais

As concreções ferro-manganosas, variáveis quanto ao diâmetro e formato, são comuns em solos desenvolvidos de calcário no norte de Minas Gerais. Normalmente, tendem a aumentar de tamanho com a profundidade nos Cambissolos e Vertissolos e a permanecer pequenas nos Latossolos, onde são mais lisas (menos corroídas) e mais arredondadas (lembrando chumbinho de caça). Com o objetivo de estudá-las, foram coletadas concreções (C) nos horizontes B de Latossolos Vermelhos; B e BC de Cambissolo e C de Vertissolo, agrupadas de acordo com o diâmetro médio (C1-Φ = 0,18 cm; C2-Φ = 0,53 cm; C3-Φ = 0,90 cm; C4-Φ = 1,75 cm), sendo C1 as concreções dos Latossolos e C2, C3 e C4 separações das concreções do Cambissolo e do Vertissolo. Tais concreções, após trituradas, foram caracterizadas química (extração de Fe e Mn com oxalato e DCB; ataque sulfúrico e ataque triácido) e mineralogicamente (difração de raios-X). Também foram coletadas amostras indeformadas dos solos que apresentavam concreções, as quais foram impregnadas para análise micromorfológica. A caracterização química das concreções revelou o ferro, a sílica e o manganês como os principais constituintes. Houve correlação significativa e negativa entre o diâmetro das concreções e o teor de ferro (r = -0,88), o que concorda com a literatura, bem como maior acúmulo de ferro nas concreções de menor diâmetro. Também houve correlação positiva entre o diâmetro e o teor de sílica (r = 0,96), fato explicado pelos teores de sílica encontrados nos solos e horizontes onde as concreções ocorrem. Para o manganês nenhuma correlação foi observada, o que contradiz dados de literatura, que revelam normalmente aumento do teor de manganês com o diâmetro. Observou-se, ainda, nas concreções, alguns elementos traços (Ba, Co, Ni, Pb). A quantificação de elementos traços demonstrou elevadas concentrações de manganês, com valores médios 40 vezes maiores que os encontrados nos solos, valores elevados de bário (em média 20 vezes maiores que nos solos) e que tendem a acompanhar o manganês (r = 0,99), o que também foi verificado para o Co (r = 0,99), Ni (r = 0,94), Pb (r = 0,99). A difração de raios-X revelou a presença de goethita como único óxido de ferro presente. Também foi detectada a presença de quartzo, caulinita, lithiophorita e traços de minerais 2:1 (possivelmente interestratificados ilita/esmectita). A micromorfologia revelou a presença de concreções (com organização interna concêntrica) e de nódulos ferro-manganosos. Observando do centro para a periferia, as camadas concêntricas das concreções variaram do preto ao amarelo-avermelhado, evidenciando a contribuição do manganês e a possível transformação dos óxidos de ferro, talvez de hematita para goethita. Alguns fragmentos de concreções presentes nos solos encontravam-se recapeados por novos aportes de ferro, indicando que o processo de difusão e concentração do ferro continuava ativo.

Composição da solução de um solo alagado conforme a profundidade e o tempo de alagamento, utilizando novo método de coleta

Na coleta da solução de solos alagados, é importante evitar o contato do oxigênio com a solução para prevenir reações redox que podem modificar sua composição química. Neste trabalho, realizado em casa de vegetação, foram feitos estudos sobre o estado de oxirredução e sobre a composição química de um Planossolo, em diferentes profundidades e tempos de alagamento, visando propor um novo método para a coleta da solução de solos alagados. O estudo foi feito em vasos plásticos com 7 kg de material de solo proveniente da camada superficial (0-20 cm), num delineamento inteiramente casualizado, com três repetições. O dispositivo de coleta da solução do solo consistiu de um tubo de polietileno com 70 cm de comprimento e 0,6 cm de diâmetro interno, com duas fileiras de orifícios de 1 mm de diâmetro, recoberto com tela de nylon de 400 mesh, construído na forma de espiral e acomodado nas profundidades de 2, 5 e 10 cm. A este dispositivo foi acoplado um sifão de vidro para a coleta da solução. Após a instalação do sistema coletor, o solo foi mantido alagado por 109 dias, tendo sido feitas coletas semanais da solução nas três profundidades. Foram analisados os valores de Eh e pH e os teores de Mn2+, Fe2+, Ca2+, Mg2+ e K+ na solução. As condições de oxirredução e os teores de cátions na solução nas diferentes profundidades, durante o período em que o solo se manteve alagado, permitiram concluir que o método utilizado pode ser indicado para coleta da solução de solos alagados, embora haja necessidade de estudos mais aprofundados sobre o assunto.