Bacteriocin-based synergetic consortia : a promising strategy to enhance antimicrobial activity and broaden the spectrum of inhibition

Bacteria-derived natural antimicrobial compounds such as bacteriocins, reruterin, and organic acids have recently received substantial attention as food preservatives or therapeutic alternatives in human or animal sectors. This study aimed to evaluate the antimicrobial activity of different bacteria-derived antimicrobials, alone or in combination, against a large panel of Gram-negative and Grampositive bacteria. Bacteriocins, including microcin J25, pediocin PA-1, nisin Z, and reuterin, were investigated alone or in combination with lactic acid and citric acid, using a checkerboard assay. Concentrations were selected based on predetermined MICs against Salmonella enterica subsp. enterica serovar Newport ATCC 6962 and Listeria ivanovii HPB28 as Gram-negative and Gram-positive indicator strains, respectively. The results demonstrated that the combination of microcin J25 1 citric acid 1 lactic acid; microcin J25 1 reuterin 1 citric acid; and microcin J25 1 reuterin 1 lactic acid tested against S. Newport ATCC 6962 showed synergistic effects (FIC index = 0.5). Moreover, a combination of pediocin PA-1 1 citric acid 1 lactic acid; and reuterin 1 citric acid 1 lactic acid against L. ivanovii HPB28 showed a partially synergistic interactions (FIC index = 0.75). Nisin Z exerted a partially synergistic effect in combination with acids (FIC index = 0.625 -0.75), whereas when it was combined with reuterin or pediocin PA-1, it showed additive effects (FIC index = 1) against L. ivanovii HPB28. The inhibitory activity of synergetic consortia were tested against a large panel of Gram-positive and Gram-negative bacteria. According to our results, combining different antimicrobials with different mechanisms of action led to higher potency and a broad spectrum of inhibition, including multidrug-resistance pathogens

Bacteriocins as a new generation of antimicrobials : toxicity aspects and regulations

In recent decades, bacteriocins have received substantial attention as antimicrobial compounds. Although bacteriocins have been predominantly exploited as food preservatives, they are now receiving increased attention as potential clinical antimicrobials and as possible immune-modulating agents. Infections caused by antibiotic-resistant bacteria have been declared as a global threat to public health. Bacteriocins represent a potential solution to this worldwide threat due to their broad- or narrow-spectrum activity against antibiotic-resistant bacteria. Notably, despite their role in food safety as natural alternatives to chemical preservatives, nisin remains the only bacteriocin legally approved by regulatory agencies as a food preservative. Moreover, insufficient data on the safety and toxicity of bacteriocins represent a barrier against the more widespread use of bacteriocins by the food and medical industry. Here, we focus on the most recent trends relating to the application of bacteriocins, their toxicity and impacts

Évolution biosédimentaire du dépôt quaternaire de la lagune de l'Ariana, Tunisie (une zone humide du Maghreb Nord)

La sebkha de l’Ariana est une lagune fermée qui fait partie des zones humides du Maghreb. Elle a une superficie de 30 à 35 km2et est située sur la bordure nord-ouest du golfe de Tunis, au sud de l’oued Medjerda. Vers 190 000 ans BP, elle a été occupée par la mer Méditerranée. Actuellement, elle en est séparée par un cordon littoral. Ce dernier s’est mis en place lors du comblement d’un golfe peu profond sous l’impulsion d’importantes quantités d’alluvions déposées par le fleuve de la Medjerda sur sa plaine deltaïque dont elle fait partie. Cette étude de l’évolution et de la dynamique de la sebkha de l’Ariana, ainsi que des changements environnementaux récents qui gouvernent la sédimentation, est basée sur une approche sédimentologique, paléontologique et isotopique. Six carottes longues de 20 m à 50 m, prélevées dans les dépôts alluviaux de la sebkha, ont fait l’objet d’une étude détaillée qui a permis de suivre la répartition spatio-temporelle du stock sédimentaire – formé essentiellement de silts argileux vaseux à la base, surmontés de sables – et de mettre en évidence des associations faunistiques particulières traduisant des modifications environnementales : environnement marin (Pléistocène moyen), lagune ouverte (Holocène) et sebkha (Actuel). Cette évolution d’un milieu marin franc vers un environnement typiquement évaporitique (sebkha) pratiquement azoïque, est probablement en rapport avec le changement climatique quaternaire.The Sebkha of Ariana, covering 30 to 35 km2is a closed lagoon, located south of the Medjerda and considered to be part of the Maghreb humid zones. It belongs to the Mediterranean coast and is positioned on the N-W margin of the Gulf of Tunis. The Sebkha is situated on Quaternary lowland resulting from the filling-up of a shallow gulf by alluvial deposits sourced from the Medjerda delta. Historically at - 190 ka, the lagoon was related to the sea but at the present time, being bunged up from the seaside by a beach barrier, is shaped to the sediments of the Madjerda low valley. The study of the evolution and the dynamics of the Ariana Sebkha as well as the recent environmental changes which have governed sedimentation are based on a sedimentological, palaeontological and isotopic approach. For that, six cores (from 20 to 50 m) were realised from four sites of the Sebkha respectively. Furthermore, correlations between the different cores throughout the lagoon have allowed the reconstruction of the spatial‑temporal distribution of sediments. The granulometric analyses revealed an alluvial sedimentation mainly composed of argillaceous silts at the base, becoming sandy towards the top. On the other hand, the benthonic fauna determinations of the six cores show a distinct evolution from an open-marine environment to a typically lagoonal environment where fauna are rare to absent. Moreover, the palaeontological study yielded particular benthonic foraminifera associations suggesting important palaeonvironmental changes which in turn are related to Quaternary climatic changes

Sedimentological analysis of marine Pleistocene deposits of southeastern Tunisia: evidence of two positive eustatic pulsations during the marine isotopic substage 5e (Eemian, Tyrrhenian)

International audienceAbstract Detailed sedimentological and petrographic analysis of marine Pleistocene deposits along the coastal area of southeastern Tunisia allow to identify two distinct lithostratigraphic units separated by an erosion surface (fig. 2 et 5 A and B). These two commonly superposed units form a ridge parallel to the coast. The palaeocoastal morphology was more irregular than the present-day coastline with areas either more protected or more exposed than now (fig. 3). The lower unit overlies an erosion surface cutting into Mio-Pliocene and Villafranchian deposits. It consists of fine-grained bioclastic quartz-rich sands (fig. 5 C), locally overlain by thin marl layers containing benthic foraminifera and ostracods. The very fine facies (silts and clays) represent relatively protected areas while the coarser facies developed in the more exposed zones. These deposits locally display a well-developed aeolian facies that terminates the sedimentary sequence. This unit, well developed in Jerba Island and Jorf peninsula, strongly resembles the stratigraphic unit of “Khnis” as defined by Mahmoudi [1988] on the coast of Central Tunisia. The upper unit is the better developed in the studied area. It consists of carbonate deposits composed mainly by ooids and peloids (fig. 5 D) and contains also a warm Senegalese fauna, especially Strombus. Locally, in the exposed areas, it shows a coarse facies which resulted mainly from the erosion of the calcareous Villafranchian deposits. This unit displays a remarkable shallowing-upward sequence from shoreface to aeolian dunes (fig. 5 E and F). It constitutes the lateral equivalent of the stratigraphic unit of “Réjiche” as defined by Mahmoudi [1988] in Central Tunisia. These two units, called in this study “quartz-rich unit” (the lower sequence) and “carbonate unit” (the upper one), developed during two distinctive sedimentation phases associated with two sea-level highstands separated by a marine regression. During the first highstand sea-level was about 3 m higher than today whereas it was at about +5 m during the second highstand [Jedoui, 2000]. Along the Mediterranean coasts the Strombus paleobeaches, which are contemporary with the carbonate unit, are well developed and traditionally called Tyrrhenian deposits. Their radiochemical dating, using corals, gives ages of about 125 ka [Hearty et al., 1986 ; Miller et al., 1986 ; Dumas et al., 1991 ; Vai et Pasini, 1996]. We obtained the most reliable uranium/thorium dates in southeastern Tunisia on oyster shells. Results show that the two units developed during the marine isotopic substage 5e [last interglacial ; Jedoui, 2000]. This evidence suggests that substage 5e was characterised by at least two eustatic maxima separated by a lowering of sea level during a marine regression. Our results are therefore in agreement with recent palaeoclimatic reconstructions and in particular with sea level reconstructions and marine oxygen isotope records that indicate the distinct possibility of two positive eustatic pulsations during the last interglacial [Hillaire-Marcel et al., 1996 ; Kindler et al., 1997 ; Plaziat et al., 1998]. Variations in the petrographic content of the two outlined units reflect drastic palaeoclimatic fluctuations in southeastern Tunisia during the last interglacial. The establishment of wetter climatic conditions at the beginning of marine isotopic substage 5e than today was responsible for an enhanced terrigenous materiel supply from the continent as showed by siliciclastic sedimentation along the coast (lower unit). Our data are in agreement with the strong sea surface salinity lowering observed in Mediterranean basins at the beginning of the last interglacial period [Kallel et al., 2000]. The regression of these conditions during the second half of the last interglacial favoured a carbonate sedimentation (upper unit) in southeastern Tunisia

CFD-driven symbolic identification of algebraic Reynolds-stress models

Reynolds-stress models (EARSM) from high-fidelity data is developed building on the frozen-training SpaRTA algorithm of [1]. Corrections for the Reynolds stress tensor and the production of transported turbulent quantities of a baseline linear eddy viscosity model (LEVM) are expressed as functions of tensor polynomials selected from a library of candidate functions. The CFD-driven training consists in solving a blackbox optimization problem in which the fitness of candidate EARSM models is evaluated by running RANS simulations. The procedure enables training models against any target quantity of interest, computable as an output of the CFD model. Unlike the frozen-training approach, the proposed methodology is not restricted to data sets for which full fields of high-fidelity data, including second flow order statistics, are available. However, the solution of a high-dimensional expensive blackbox function optimization problem is required. Several steps are then undertaken to reduce the associated computational burden. First, a sensitivity analysis is used to identify the most influential terms and to reduce the dimensionality of the search space. Afterwards, the Constrained Optimization using Response Surface (CORS) algorithm, which approximates the black-box cost function using a response surface constructed from a limited number of CFD solves, is used to find the optimal model parameters. Model discovery and cross-validation is performed for three configurations of 2D turbulent separated flows in channels of variable section using different sets of training data to show the flexibility of the method. The discovered models are then applied to the prediction of an unseen 2D separated flow with higher Reynolds number and different geometry. The predictions of the discovered models for the new case are shown to be not only more accurate than the baseline LEVM, but also of a multi-purpose EARSM model derived from purely physical arguments. The proposed deterministic symbolic identification approach constitutes a promising candidate for building accurate and robust RANS models customized for a given class of flows at moderate computational cost. ©2022 Elsevier Inc. All rights reserved

Evolution of olivine lattice preferred orientation during simple shear in the mantle

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 272 (2008): 501-512, doi:10.1016/j.epsl.2008.03.063.Understanding the variation of olivine lattice preferred orientation (LPO) as a function of shear strain is important for models that relate seismic anisotropy to the kinematics of deformation. We present results on the evolution of olivine orientation as a function of shear strain in samples from a shear zone in the Josephine Peridotite (southwest Oregon). We find that the LPO in harzburgites re-orients from a pre-existing LPO outside the shear zone to a new LPO with the olivine [100] maximum aligned sub-parallel to the shear direction between 168% and 258% shear strain. The strain at which [100] aligns with the shear plane is slightly higher than that observed in experimental samples, which do not have an initial LPO. While our observations broadly agree with the experimental observations, our results suggest that a pre-existing LPO influences the strain necessary for LPO alignment with the shear direction. In addition, olivine re-alignment appears to be dominated by slip on both (010)[100] and (001)[100], due to the orientation of the pre-existing LPO. Fabric strengths, quantified using both the J- and M- indices, do not increase with increasing shear strain. Unlike experimental observations, our natural samples do not have a secondary LPO peak. The lack of a secondary peak suggests that subgrain rotation recrystallization dominates over grain boundary migration during fabric re-alignment. Harzburgites exhibit girdle patterns among [010] and [001] axes, while a dunite has point maxima. Combined with the observation that harzburgites are finer grained than dunites, we speculate that additional phases (i.e., pyroxenes) limit olivine grain growth and promote grain boundary sliding. Grain boundary sliding may relax the requirement for slip on the hardest olivine system, enhancing activation of the two easiest olivine slip systems, resulting in the [010] and [001] girdle patterns. Overall, our results provide an improved framework for calibration of LPO evolution models.This work was partly supported by NSF grants EAR-0230267 and EAR-0409609. Funding for fieldwork was provided by the WHOI Academic Programs Office as part of a 2003 field class run by P.B.K. and G.H

Shear wave splitting across the Iceland hot spot: Results from the ICEMELT experiment

We report on observations of upper mantle anisotropy from the splitting of teleseismic shear waves (SKS, SKKS, and PKS) recorded by the ICEMELT broadband seismometer network in Iceland. In a ridge-centered hot spot locale, mantle anisotropy may be generated by flow-induced lattice-preferred orientation of olivine grains or the anisotropic distribution of magma. Splitting measurements of teleseismic shear waves may thus provide diagnostic information on upper mantle flow and/or the distribution of retained melt associated with the Iceland mantle plume. In eastern Iceland, fast polarization directions lie between N10°W and N45°W and average N24°W; delay times between the fast and slow shear waves are generally 0.7–1.35 s. In western Iceland, in contrast, the fast polarization directions, while less well constrained, yield an average value of N23°E and delay times are smaller (0.2–0.95 s). We propose that splitting in eastern Iceland is caused by a 100- to 200-km-thick anisotropic layer in the upper mantle. The observed fast directions in eastern Iceland, however, do not correspond either to the plate spreading direction or to a pattern of radial mantle flow from the center of the Iceland hot spot. We suggest that the relatively uniform direction and magnitude of splitting in eastern Iceland, situated on the Eurasian plate, may therefore reflect the large-scale flow field of the North Atlantic upper mantle. We hypothesize that the different pattern of anisotropy beneath western Iceland, part of the North American plate, is due to the different absolute motions of the two plates. By this view, splitting in eastern and western Iceland is the consequence of shear by North American and Eurasian plate motion relative to the background mantle flow. From absolute plate motion models, in which the Eurasian plate is approximately stationary and the North American plate is moving approximately westward, the splitting observations in both eastern and western Iceland can be satisfied by a background upper mantle flow in the direction N34°W and a velocity of 3 cm/yr in a hot spot reference frame. This inference can be used to test mantle flow models. In particular, it is inconsistent with kinematic flow models, which predict southward flow, or models where flow is dominated by subduction-related sources of mantle buoyancy, which predict westward flow. Our observations are more compatible with the flow field predicted from global seismic tomography models, which in particular include the influence of the large-scale lower mantle upwelling beneath southern Africa. While the hypothesized association between our observations and this upwelling is presently speculative, it makes a very specific and testable prediction about the flow field and hence anisotropy beneath the rest of the Atlantic basin.This work was supported by the National Science Foundation under grants EAR-9316137, OCE-9402991, and EAR-9707193.Peer Reviewe

Pooled analysis of iron-related genes in Parkinson's disease: Association with transferrin

Pathologic features of Parkinson's disease (PD) include death of dopaminergic neurons in the substantia nigra, presence of α-synuclein containing Lewy bodies, and iron accumulation in PD-related brain regions. The observed iron accumulation may be contributing to PD etiology but it also may be a byproduct of cell death or cellular dysfunction. To elucidate the possible role of iron accumulation in PD, we investigated genetic variation in 16 genes related to iron homeostasis in three case-control studies from the United States, Australia, and France. After screening 90 haplotype tagging single nucleotide polymorphisms (SNPs) within the genes of interest in the US study population, we investigated the five most promising gene regions in two additional independent case-control studies. For the pooled data set (1289 cases, 1391 controls) we observed a protective association (OR. = 0.83, 95% CI: 0.71-0.96) between PD and a haplotype composed of the A allele at rs1880669 and the T allele at rs1049296 in transferrin (TF; GeneID: 7018). Additionally, we observed a suggestive protective association (OR. = 0.87, 95% CI: 0.74-1.02) between PD and a haplotype composed of the G allele at rs10247962 and the A allele at rs4434553 in transferrin receptor 2 (TFR2; GeneID: 7036). We observed no associations in our pooled sample for haplotypes in SLC40A1, CYB561, or HFE. Taken together with previous findings in model systems, our results suggest that TF or a TF- TFR2 complex may have a role in the etiology of PD, possibly through iron misregulation or mitochondrial dysfunction within dopaminergic neurons