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Environmental uranium pollution due to industries producing naturally occurring radioactive material or nuclear accidents and releases is a global concern. Uranium is hazardous for ecosystems as well as for humans when accumulated through the food chain, through contaminated groundwater and potable water sources, or through inhalation. In particular, uranium pollution pressures microbial communities, which are essential for healthy ecosystems. In turn, microorganisms can influence the mobility and toxicity of uranium through processes like biosorption, bioreduction, biomineralization, and bioaccumulation. These processes were characterized by studying the interaction of different bacteria with uranium. However, most studies unraveling the underlying molecular mechanisms originate from the last decade. Molecular mechanisms help to understand how bacteria interact with radionuclides in the environment. Furthermore, knowledge on these underlying mechanisms could be exploited to improve bioremediation technologies. Here, we review the current knowledge on bacterial uranium resistance and how this could be used for bioremediation applications.

12 Páginas, 7 Figuras. Contiene información suplementaria en: http://dx.doi.org/10.1038/s41467-018-02949-y, Bacteria use two-component systems (TCSs) to sense and respond to environmental changes. The core genome of the major human pathogen Staphylococcus aureus encodes 16 TCSs, one of which (WalRK) is essential. Here we show that S. aureus can be deprived of its complete sensorial TCS network and still survive under growth arrest conditions similarly to wild-type bacteria. Under replicating conditions, however, the WalRK system is necessary and sufficient to maintain bacterial growth, indicating that sensing through TCSs is mostly dispensable for living under constant environmental conditions. Characterization of S. aureus derivatives containing individual TCSs reveals that each TCS appears to be autonomous and self-sufficient to sense and respond to specific environmental cues, although some level of cross-regulation between non-cognate sensor-response regulator pairs occurs in vivo. This organization, if confirmed in other bacterial species, may provide a general evolutionarily mechanism for flexible bacterial adaptation to life in new niches., This work was supported by the Spanish Ministry of Economy and Competitiveness grants BIO2011-30503-C02-02, BIO2014-53530-R, SAF2014-56716-REDT , and RTC-2015-3184-1. J.V. was supported by Ramon y Cajal (RYC-2009-03948) contract from the Spanish Ministry of Economy and Competitiveness.

Understanding the mechanism of cell migration and interaction with the microenvironment is not only of critical significance to the function and biology of cells, but also has extreme relevance and impact on physiological processes and diseases such as morphogenesis, wound healing, neuron guidance, and cancer metastasis. External guidance factors such as topography and physical cues of the microenvironment promote directional migration and can target specific changes in cell motility and signalling mechanisms. Recent studies have shown that cells can directionally respond to applied electric fields (EFs), in both in vitro and in vivo settings, a phenomenon called electrotaxis. However, the exact cellular mechanisms for sensing electrical signals are still not fully well understood, and it is thus far unknown how cells recognize and respond to electric fields, although some studies have suggested that electro-migration of some cell surface receptors and ion channels in cells could be involved. Applied electric fields may have a potential clinical role in guiding cell migration and present a more precise manageability to change the magnitude and direction of the electric field than most other guidance cues such as chemical cues. Here we present a review of recent studies used for studying electrotaxis to point out similarities, identify points of disagreement, and stimulate new directions for investigation. Insights into the mechanisms by which applied EFs direct cell migration, morphological change and development will enable current and future therapeutic applications to be optimized.

International audience; o understand how atmospheric dust deposition and ultraviolet radiation (UVR) can affect remote, freshwater ecosystems through changes in their microbial metabolism, it is important to have tools that allow us detecting alterations and anticipating potential shifts in the functioning of microbial communities. Ecoenzyme activities (EA) are easy to measure and their ratios can be used to assess system microbial metabolism of freshwater bodies, thus evaluating the effects of global change stressors. We carried out an in situ full factorial experiment to determine how the interaction between the addition of C and P, and UVR affect the microbial metabolism of a Mediterranean high-mountain lake. Overall, activities of five ecoenzymes involved in the degradation of C-compounds and in the acquisition of N and P revealed that, under natural conditions, the growth of heterotrophic prokaryotes was dependent on organic compounds released by algae, which is consistent with a higher constraint of bacterial carbon production by C than by P or N, as suggested by EA ratios. Accordingly, the addition of a labile C source did not lead to any significant response of microbial communities, but the addition of P provoked a clear change in the microbial metabolism of the lake, promoting the growth of phytoplankton and leading heterotrophic prokaryotes to be more constrained by P, and to a lesser extent by N, in relation to C. UVR played a secondary role, probably because microbial communities inhabiting high-mountain lakes possess several evolutionary adaptations to high UVR levels. Changes in the microbial metabolism of our model lake under different scenarios of nutrient inputs and UVR can therefore be evaluated by EA ratios.

International audience; In Escherichia coli, only one essential oligoribonuclease (Orn) can degrade oligoribonucleotides of five residues and shorter in length (nanoRNA). In Bacillus subtilis, NrnA and NrnB, which do not show any sequence similarity to Orn, have been identified as functional analogues of Orn. Sequence comparisons did not identify orn, nrnA or nrnB homologues in the genomes of the Chlamydia/Cyanobacteria and Alphaproteobacteria family members. Screening a genomic library from Bartonella birtlesii, a member of the Alphaproteobacteria, for genes that can complement a conditional orn mutant in E. coli, we identified BA0969 (NrnC) as a functional analogue of Orn. NrnC is highly conserved (more than 80 % identity) in the Bartonella genomes sequenced to date. Biochemical characterization showed that this protein exhibits oligo RNA degradation activity (nanoRNase activity). Like Orn from E. coli, NrnC is inhibited by micromolar amounts of 3'-phosphoadenosine 5'-phosphate in vitro. NrnC homologues are widely present in genomes of Alphaproteobacteria. Knock down of nrnC decreases the growth ability of Bartonella henselae, demonstrating the importance of nanoRNase activity in this bacterium.

Depolarization of nerve terminals stimulates rapid dephosphorylation of two isoforms of dynamin I (dynI), mediated by the calcium-dependent phosphatase calcineurin (CaN). Dephosphorylation at the major phosphorylation sites Ser-774/778 promotes a dynI-syndapin I interaction for a specific mode of synaptic vesicle endocytosis called activity-dependent bulk endocytosis (ADBE). DynI has two main splice variants at its extreme C terminus, long or short (dynIxa and dynIxb) varying only by 20 (xa) or 7 (xb) residues. Recombinant GST fusion proteins of dynIxa and dynIxb proline-rich domains (PRDs) were used to pull down interacting proteins from rat brain nerve terminals. Both bound equally to syndapin, but dynIxb PRD exclusively bound to the catalytic subunit of CaNA, which recruited CaNB. Binding of CaN was increased in the presence of calcium and was accompanied by further recruitment of calmodulin. Point mutations showed that the entire C terminus of dynIxb is a CaN docking site related to a conserved CaN docking motif (PXIXI(T/S)). This sequence is unique to dynIxb among all other dynamin variants or genes. Peptide mimetics of the dynIxb tail blocked CaN binding in vitro and selectively inhibited depolarization-evoked dynI dephosphorylation in nerve terminals but not of other dephosphins. Therefore, docking to dynIxb is required for the regulation of both dynI splice variants, yet it does not regulate the phosphorylation cycle of other dephosphins. The peptide blocked ADBE, but not clathrin-mediated endocytosis of synaptic vesicles. Our results indicate that Ca(2+) influx regulates assembly of a fully active CaN-calmodulin complex selectively on the tail of dynIxb and that the complex is recruited to sites of ADBE in nerve terminals.

The protein phosphatase calcineurin has been gradually revealing itself as the central controller of our immune response, although it is involved in a wide array of signaling pathways related to cellular development and cell cycle progression. As such, calcineurin is an attractive, yet delicate, therapeutic target for the prevention of allograft rejection and treatment of several inflammatory skin conditions. However, calcineurin activity is not only sensitive to immunosuppressants such as cyclosporin A and tacrolimus, but also subject to modulation by reactive oxygen species. We have recently shown, both in vivo and in vitro, that UVA1 radiation suppresses calcineurin activity. In this paper, we present evidence that this activity loss is due to singlet oxygen and superoxide generated by photosensitization and show that a closely related phosphatase, PP2A, is not affected. Furthermore, a survey of this damage reveals oxidation of several Met and Cys residues as well as an overall conformational change. These findings provide a mechanistic basis for the hypothesis that UVA1 and calcineurin inhibitors both affect the same signal transduction pathway in skin. (C) 2011 Elsevier Inc. All rights reserved.

Major factors that constrain tropical soil fertility and sustainable agriculture are low nutrient capital, moisture stress, erosion, high P fixation, high acidity with aluminium toxicity, and low soil biodiversity. The fragility of many tropical soils limits food production in annual cropping systems. Because some tropical soils under natural conditions have high biological activity, an increased use of the biological potential of these soils to counter the challenges of food production problems is proposed. Most plant species (including the major crops in the tropics) form beneficial associations with arbuscular mycorrhizal (AM) fungi. These fungi could be the most important and poorly understood resource for nutrient acquisition and plant growth in agriculture. This review treats the role of AM fungi in enhancing physical, chemical, and biological soil quality. It focuses on the roles of AM in maintenance and improvement of soil structure, the uptake of relatively immobile elements, both macronutrients (phosphorus) and micronutrients (zinc), the alleviation of aluminium and manganese toxicity, the interactions with other beneficial soil organisms (nitrogen-fixing rhizobia), and improved protection against pathogens. Mycorrhizal associations enable a better use of sparingly soluble phosphorus pools, thereby increasing the efficiency of added phosphorus fertilizer and of the large relatively immobile phosphorus pools. Mycorrhizal management through agroforestry, reduced soil disturbance or crop rotation, is often a better option than mycorrhizal inoculation, considering the problems and costs of large-scale inoculum production. Research directions that are needed to increase understanding of mycorrhizal associations in tropical cropping systems and to increase mycorrhizal benefit are indicated.

We studied glomerular ATPase activity, as detectable at the light microscopic (LM) level in cryostat sections of the rat kidney, after unilateral local X-irradiation. The biochemically detectable reduction in glomerular ATPase activity after X-irradiation could be demonstrated at the LM level by application of a modified cerium-based technique. Results show a clear reduction of reaction product in glomeruli in X-irradiated kidneys as compared with the contralateral control kidney. Technical parameters (i.e., tissue fixation, second thickness, cerium concentration of the incubation mixture, and percentage H2O2 added for the amplification step) were established for optimal reproducibility of the staining results. We show that this modified staining protocol allows detection of differences of ATPase activity in contrast to conventional histochemical methods. Inhibition studies with various phosphatase inhibitors and competitive substrate inhibition experiments revealed that the enzyme is specific for nucleoside di- and triphosphatases. Since reduced glomerular adenine nucleotidase activity has recently been recognized as an early event in (experimental) glomerulonephritis, we feel that the new staining protocol presented here may be highly relevant for routine tissue section screening in nephropathological research.

The protein farnesyltransferase (FTase) is a Zn(2+)-metalloenzyme that catalyzes the farnesylation reaction, i.e., the transfer of the 15-carbon atom farnesyl group from farnesyl diphosphate (FPP) to a specific cysteine of protein substrates. Oncogenic Ras proteins, which are among the FTase substrates, are observed in about 20-30% of human cancer cells. Thus, FTase represents a target for anticancer drug design. Herein, we present a classical force-field-based and quantum mechanics/molecular mechanics (QM/MM) computational study of the FTase reaction mechanism. Our findings offer a detailed picture of the FTase catalytic pathway, describing structural features and the energetics of its saddle points. A moderate dissociation of the diphosphate group from the FPP is observed during the nucleophilic attack of the zinc-bound thiolate. At the transition state, a resonance structure is observed, which indicates the formation of a metastable carbocation. However, no stable intermediate is found along the reaction pathway. Thus, the reaction occurs via an associative mechanism with dissociative character, in agreement with the mechanism proposed by Fierke et al. ( Biochemistry 2000, 39, 2593-2602 and Biochemistry 2003, 42, 9741-9748 ). Moreover, a fluorine-substituted FPP analogue (CF3-FPP) is used to investigate the inhibitory effect of fluorine, which in turn provides additional agreement with experimental data.

During cell life, membranes are subjected to a variable and inhomogeneous environment. These local variations can be strongly related to biological processes. For instance, in the inner membrane of mitochondria, ATP synthesis is tightly coupled to the local pH. It is therefore interesting to study the response of a lipid membrane to a local modification of its environment.In our previous works (Khalifat et al., Biophys. J., 2008; Fournier et al., PRL, 2009; Bitbol et al., J. Phys.: Condens. Matter, 2011), we designed an experiment where the local pH at an artificial membrane (lipid giant unilamellar vesicle) is modified using microinjection. We showed that modifying the local pH induced a dynamic membrane deformation. We also developed a theoretical description of the dynamics of a membrane subjected to a local modification affecting its physical properties. It involved elaborating a local version of the area-difference elasticity model and accounting for the friction between the two monolayers of the bilayer membrane.We have now extended our theoretical model to account for the diffusion of the membrane-modifying reagent in the surrounding solution. We solved numerically the equations describing the dynamics of the membrane in this case. We showed that the effect of diffusion from the local reagent source is generally important, but that there are experimentally accessible cases where the dynamics is dominated by processes intrinsic to the membrane, such as the relative sliding of its two monolayers. We compared the predictions of our extended theoretical model to experimental results regarding the dynamics of lipid (PC/PS-) membrane deformation during and just after the local delivery of a basic solution. Moreover, we used a pH-sensitive fluorescent membrane marker to have a direct experimental visualization of the membrane pH profile together with the deformation.