The bactericidal effect of TiO2 photocatalysis involves adsorption onto catalyst and the loss of membrane integrity

The bactericidal effect of photocatalysis with TiO2 is well recognized, although its mode of action is still poorly characterized. It may involve oxidation, as illuminated TiO2 generates reactive oxygen species. Here we analyze the bactericidal effect of illuminated TiO2 in NaCl-KCl or sodium phosphate solutions. We found that adsorption of bacteria on the catalyst occurred immediately in NaCl-KCl solution, whereas it was delayed in the sodium phosphate solution. We also show that the rate of adsorption of cells onto TiO2 is positively correlated with its bactericidal effect. Importantly, adsorption was consistently associated with a reduction or loss of bacterial membrane integrity, as revealed by flow cytometry. Our work suggests that adsorption of cells onto aggregated TiO2, followed by loss of membrane integrity, is key to the bactericidal effect of photocatalysi

Characterization of Halorubrum sfaxense sp. nov., a New Halophilic Archaeon Isolated from the Solar Saltern of Sfax in Tunisia

An extremely halophilic archaeon, strain ETD6, was isolated from a marine solar saltern in Sfax, Tunisia. Analysis of the 16S rRNA gene sequence showed that the isolate was phylogenetically related to species of the genus Halorubrum among the family Halobacteriaceae, with a close relationship to Hrr. xinjiangense (99.77% of identity). However, value for DNA-DNA hybridization between strain ETD6 and Hrr.xinjiangense were about 24.5%. The G+C content of the genomic DNA was 65.1 mol% (T(m)). Strain ETD6 grew in 15–35% (w/v) NaCl. The temperature and pH ranges for growth were 20–55°C and 6–9, respectively. Optimal growth occurred at 25% NaCl, 37°C, and pH 7.4. The results of the DNA hybridization against Hrr. xinjiangense and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain ETD6 from other Hrr. species. Therefore, strain ETD6 represents a novel species of the genus Halorubrum, for which the name Hrr. sfaxense sp. nov. is proposed. The Genbank EMBL-EBI accession number is GU724599

Characterization of heterotrophic prokaryote subgroups in the Sfax coastal solar salterns by combining flow cytometry cell sorting and phylogenetic analysis

Here, we combined flow cytometry (FCM) and phylogenetic analyses after cell sorting to characterize the dominant groups of the prokaryotic assemblages inhabiting two ponds of increasing salinity: a crystallizer pond (TS) with a salinity of 390 g/L, and the non-crystallizer pond (M1) with a salinity of 200 g/L retrieved from the solar saltern of Sfax in Tunisia. As expected, FCM analysis enabled the resolution of high nucleic acid content (HNA) and low nucleic acid content (LNA) prokaryotes. Next, we performed a taxonomic analysis of the bacterial and archaeal communities comprising the two most populated clusters by phylogenetic analyses of 16S rRNA gene clone library. We show for the first time that the presence of HNA and LNA content cells could also be extended to the archaeal populations. Archaea were detected in all M1 and TS samples, whereas representatives of Bacteria were detected only in LNA for M1 and HNA for TS. Although most of the archaeal sequences remained undetermined, other clones were most frequently affiliated to Haloquadratum and Halorubrum. In contrast, most bacterial clones belonged to the Alphaproteobacteria class (Phyllobacterium genus) in M1 samples and to the Bacteroidetes phylum (Sphingobacteria and Salinibacter genus) in TS samples

Rules Governing Selective Protein Carbonylation

BACKGROUND:Carbonyl derivatives are mainly formed by direct metal-catalysed oxidation (MCO) attacks on the amino-acid side chains of proline, arginine, lysine and threonine residues. For reasons unknown, only some proteins are prone to carbonylation. METHODOLOGY/PRINCIPAL FINDINGS:we used mass spectrometry analysis to identify carbonylated sites in: BSA that had undergone in vitro MCO, and 23 carbonylated proteins in Escherichia coli. The presence of a carbonylated site rendered the neighbouring carbonylatable site more prone to carbonylation. Most carbonylated sites were present within hot spots of carbonylation. These observations led us to suggest rules for identifying sites more prone to carbonylation. We used these rules to design an in silico model (available at http://www.lcb.cnrs-mrs.fr/CSPD/), allowing an effective and accurate prediction of sites and of proteins more prone to carbonylation in the E. coli proteome. CONCLUSIONS/SIGNIFICANCE:We observed that proteins evolve to either selectively maintain or lose predicted hot spots of carbonylation depending on their biological function. As our predictive model also allows efficient detection of carbonylated proteins in Bacillus subtilis, we believe that our model may be extended to direct MCO attacks in all organisms

A Microscope Automated Fluidic System to Study Bacterial Processes in Real Time

Most time lapse microscopy experiments studying bacterial processes ie growth, progression through the cell cycle and motility have been performed on thin nutrient agar pads. An important limitation of this approach is that dynamic perturbations of the experimental conditions cannot be easily performed. In eukaryotic cell biology, fluidic approaches have been largely used to study the impact of rapid environmental perturbations on live cells and in real time. However, all these approaches are not easily applicable to bacterial cells because the substrata are in all cases specific and also because microfluidics nanotechnology requires a complex lithography for the study of micrometer sized bacterial cells. In fact, in many cases agar is the experimental solid substratum on which bacteria can move or even grow. For these reasons, we designed a novel hybrid micro fluidic device that combines a thin agar pad and a custom flow chamber. By studying several examples, we show that this system allows real time analysis of a broad array of biological processes such as growth, development and motility. Thus, the flow chamber system will be an essential tool to study any process that take place on an agar surface at the single cell level

TiO2 Photocatalysis Causes DNA Damage via Fenton Reaction-Generated Hydroxyl Radicals during the Recovery Period▿

Here, we show that resistance of Escherichia coli to TiO2 photocatalysis involves defenses against reactive oxygen species. Results support the idea that TiO2 photocatalysis generates damage which later becomes deleterious during recovery. We found this to be partly due to DNA attack via hydroxyl radicals generated by the Fenton reaction during recovery

Viabilité et cultivabilité de L. pneumophila (étude des mécanismes impliqués dans la récupération de l'aptitude à former des colonies)

Legionella pneumophila est une bactérie pathogène responsable de la légionellose qui se transmet par voies aériennes à partir de sites industriels ou naturels générateurs d'aérosols (installation d'eau chaude sanitaire, tours aéroréfrigérantes, ...). Actuellement le dénombrement et l'isolement de L. pneumophila sont régis par une norme basée sur l'utilisation de culture gélosés. Cependant, comme de très nombreuses bactéries Gram négatif, Legionella pneumophila serait capable de passer, en condition de carence ou de stress, dans un état viable mais non cultivable (VBNC). Au cours de cette étude, nou avons montré que les différents traitements biocides classiquement utilisés pour éradiquer L. pneumophila dans les installations industrielles, induisaient la formation de cellules VBNC, déterminées à travers l'utilisation de marqueurs de viabilité et du milieu de culture de référence. Cependant, l'analyse fine des marqueurs de viabilité estimée pour chaque cellule viable détectée montre que celles-ci présentent une altération progressive des différents descripteurs de viabilité utilisés à mesure que la concentration en biocide augmente. En supposant dans un premier temps, que la perte de cultivabilité des cellules VBNC soit potentiellement due au stress oxydant généré lors que l'étalement, nous avons cherché à optimiser le milieu de référence. Au cours de cette étude de nombreux composés (antioxudants, métaboliques...) ont ainsi été identifiés comme étant bénéfiques à la restauration de la cultivabilité d'une fonction de la population après un stress mais aussi, et de manière intéressante, au cours de la croissance. La co-existence de deux sous population cultivables (sur le milieu de référence ou supplémenté) dont la proportion relative évolue au cours du temps, soulève donc à ce jour, un certain nombre de questions quant à l'origine et à la pertinence physiologique de chacune des deux populations. Pour des raisons techniques, ces questions ne pourrons être résolues qu'à travers l'utilisation de méthodes centrées sur l'individu et non plus sur la réponse globale d'une population. Dans ce sens, nous avons initié le développement d'une chambre d'observation et d'un système de fluidique qui permet aujourd'hui un suivi en temps réel de la viabilité des cellules observé et de leur devenir au cours du temps ou au cours d'un stress tout en observant in fine leur capacité respective à former une colonieLegionella pneumophila is the causative agent of Legionellosis transmitted by air from industrial or natural aerosols (installation of hot water, cooling towers ...) Currently standard procedure that uses the agar cultur media governs the detection and isolation of L. Pneumophila. However, like many Gram-negative bacteria, Legionella pneumophila is able to enter in a viable state but non culturable (VBNC) during starvation or stress conditions. In this study, we showed that the different treatment biocides traditionally used to eradicate. L. pneumophila in industrial plants, induced the formation of VBNC cells, determined using viability markers and reference agar medium (BCYE). However, detailled analysis of the viability markers shows that they have a progressive detetioration of the viability of different descriptors used as the biocide concentration increases. Assuming initially that the loss of culturability of VBNC cells is potentially due to oxidative stress generated during spreading, we sought to optimize the reference medium. During the study many compounds (antioxidants, metabolic ...) have been identified as benefical to the restoration of culturability for a fraction of the population after stress but also, interestingly, during growth. The co-existence of two populations (culturable on the reference medium or the supplemented medium) with the relative proportion changes over time, raises to date, a number of questions about the origin and physiological relevance of each of the two populations. For technical reasons, these issues can be resolved only with methods focused on the individual rather than on the overall response of a population. In this sense, we initiated the development of an observation chamber and a fluidic system that now allows as realtime monitoring of cell viability observed and their evolution over time or during a stress while observing ultimately their respective ability to form a colonyAIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Mise en évidence d'une fraction agrégée présentant un enrichissement en protéines anormales et/ou oxydées chez Escherichia coli en phase exponentielle de croissance

AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF