Journals
2012 EN
J. Timothy Wootton · Catherine A. Pfister
We explored changes in ocean pH in coastal Washington state, USA, by extending a decadal-scale pH data series, by reporting independent measures of dissolved inorganic carbon (DIC), spectrophotometric pH, and total alkalinity (TA), by exploring pH patterns over larger spatial scales, and by probing for long-term trends in environmental variables reflecting potentially important drivers of pH. We found that pH continued to decline in this area at a rapid rate, that pH exhibited high natural variability within years, that our measurements of pH corresponded well to spectrophotometric pH measures and expected pH calculated from DIC/TA, and that TA estimates based on salinity predicted well actual alkalinity. Multiple datasets reflecting upwelling, including water temperature, nutrient levels, phytoplankton abundance, the NOAA upwelling index, and data on local wind patterns showed no consistent trends over the period of our study. Multiple datasets reflecting precipitation change and freshwater runoff, including precipitation records, local and regional river discharge, salinity, nitrate and sulfate in rainwater, and dissolved organic carbon (DOC) in rivers also showed no consistent trends over time. Dissolved oxygen did not decline over time, indicating that long-term changes did not result from shifts in contributions of respiration to pH levels. These tests of multiple potential drivers of the observed rapid rate of pH decline indicate a primary role for inorganic carbon and suggest that geochemical models of coastal ocean carbon fluxes need increased investigation.
Public Library of Science
Journals
2012 EN
Fabien BaldacciCresp · Christine Chang · Mickaël Maucourt
+11 more
Root-knot nematodes (RKN) are obligatory plant parasitic worms that establish and maintain an intimate relationship with their host plants. During a compatible interaction, RKN induce the redifferentiation of root cells into multinucleate and hypertrophied giant cells essential for nematode growth and reproduction. These metabolically active feeding cells constitute the exclusive source of nutrients for the nematode. Detailed analysis of glutathione (GSH) and homoglutathione (hGSH) metabolism demonstrated the importance of these compounds for the success of nematode infection in Medicago truncatula . We reported quantification of GSH and hGSH and gene expression analysis showing that (h)GSH metabolism in neoformed gall organs differs from that in uninfected roots. Depletion of (h)GSH content impaired nematode egg mass formation and modified the sex ratio. In addition, gene expression and metabolomic analyses showed a substantial modification of starch and γ-aminobutyrate metabolism and of malate and glucose content in (h)GSH-depleted galls. Interestingly, these modifications did not occur in (h)GSH-depleted roots. These various results suggest that (h)GSH have a key role in the regulation of giant cell metabolism. The discovery of these specific plant regulatory elements could lead to the development of new pest management strategies against nematodes.
Public Library of Science
Journals
2012 EN
MarCia T. Ekworomadu · Catherine B. Poor · Cedric P. Owens
+9 more
To replicate in mammalian hosts, bacterial pathogens must acquire iron. The majority of iron is coordinated to the protoporphyrin ring of heme, which is further bound to hemoglobin. Pathogenic bacteria utilize secreted hemophores to acquire heme from heme sources such as hemoglobin. Bacillus anthracis , the causative agent of anthrax disease, secretes two hemophores, IsdX1 and IsdX2, to acquire heme from host hemoglobin and enhance bacterial replication in iron-starved environments. Both proteins contain NEAr-iron Transporter (NEAT) domains, a conserved protein module that functions in heme acquisition in Gram-positive pathogens. Here, we report the structure of IsdX1, the first of a Gram-positive hemophore, with and without bound heme. Overall, IsdX1 forms an immunoglobin-like fold that contains, similar to other NEAT proteins, a 3 10 -helix near the heme-binding site. Because the mechanistic function of this helix in NEAT proteins is not yet defined, we focused on the contribution of this region to hemophore and NEAT protein activity, both biochemically and biologically in cultured cells. Site-directed mutagenesis of amino acids in and adjacent to the helix identified residues important for heme and hemoglobin association, with some mutations affecting both properties and other mutations affecting only heme stabilization. IsdX1 with mutations that reduced the ability to associate with hemoglobin and bind heme failed to restore the growth of a hemophore-deficient strain of B. anthracis on hemoglobin as the sole iron source. These data indicate that not only is the 3 10 -helix important for NEAT protein biology, but also that the processes of hemoglobin and heme binding can be both separate as well as coupled, the latter function being necessary for maximal heme-scavenging activity. These studies enhance our understanding of NEAT domain and hemophore function and set the stage for structure-based inhibitor design to block NEAT domain interaction with upstream ligands.
Public Library of Science
Journals
2012 EN
Radovan Fišer · Jiří Mašín · Ladislav Bumba
+11 more
Bordetella adenylate cyclase toxin-hemolysin (CyaA) penetrates the cytoplasmic membrane of phagocytes and employs two distinct conformers to exert its multiple activities. One conformer forms cation-selective pores that permeabilize phagocyte membrane for efflux of cytosolic potassium. The other conformer conducts extracellular calcium ions across cytoplasmic membrane of cells, relocates into lipid rafts, translocates the adenylate cyclase enzyme (AC) domain into cells and converts cytosolic ATP to cAMP. We show that the calcium-conducting activity of CyaA controls the path and kinetics of endocytic removal of toxin pores from phagocyte membrane. The enzymatically inactive but calcium-conducting CyaA-AC − toxoid was endocytosed via a clathrin-dependent pathway. In contrast, a doubly mutated (E570K+E581P) toxoid, unable to conduct Ca 2+ into cells, was rapidly internalized by membrane macropinocytosis, unless rescued by Ca 2+ influx promoted in trans by ionomycin or intact toxoid. Moreover, a fully pore-forming CyaA-ΔAC hemolysin failed to permeabilize phagocytes, unless endocytic removal of its pores from cell membrane was decelerated through Ca 2+ influx promoted by molecules locked in a Ca 2+ -conducting conformation by the 3D1 antibody. Inhibition of endocytosis also enabled the native B. pertussis -produced CyaA to induce lysis of J774A.1 macrophages at concentrations starting from 100 ng/ml. Hence, by mediating calcium influx into cells, the translocating conformer of CyaA controls the removal of bystander toxin pores from phagocyte membrane. This triggers a positive feedback loop of exacerbated cell permeabilization, where the efflux of cellular potassium yields further decreased toxin pore removal from cell membrane and this further enhances cell permeabilization and potassium efflux.
Public Library of Science
Journals
2012 EN
Rushika Perera · Catherine Riley · Giorgis Isaac
+7 more
Dengue virus causes ∼50–100 million infections per year and thus is considered one of the most aggressive arthropod-borne human pathogen worldwide. During its replication, dengue virus induces dramatic alterations in the intracellular membranes of infected cells. This phenomenon is observed both in human and vector-derived cells. Using high-resolution mass spectrometry of mosquito cells, we show that this membrane remodeling is directly linked to a unique lipid repertoire induced by dengue virus infection. Specifically, 15% of the metabolites detected were significantly different between DENV infected and uninfected cells while 85% of the metabolites detected were significantly different in isolated replication complex membranes. Furthermore, we demonstrate that intracellular lipid redistribution induced by the inhibition of fatty acid synthase, the rate-limiting enzyme in lipid biosynthesis, is sufficient for cell survival but is inhibitory to dengue virus replication. Lipids that have the capacity to destabilize and change the curvature of membranes as well as lipids that change the permeability of membranes are enriched in dengue virus infected cells. Several sphingolipids and other bioactive signaling molecules that are involved in controlling membrane fusion, fission, and trafficking as well as molecules that influence cytoskeletal reorganization are also up regulated during dengue infection. These observations shed light on the emerging role of lipids in shaping the membrane and protein environments during viral infections and suggest membrane-organizing principles that may influence virus-induced intracellular membrane architecture.
Public Library of Science
Journals
2012 EN
Paul V. Licciardi · Zheng Quan Toh · Eileen M. Dunne
+5 more
Streptococcus pneumoniae (the pneumococcus) is a predominant cause of pneumonia, meningitis, and bacteremia. It is a leading killer of children under 5 years of age, responsible for the deaths of up to 2 million children annually [1]. Most deaths occur in African and Asian developing countries; however, pneumococcal disease is also a significant problem in particular populations of developed countries, such as the North American Indians, and indigenous Alaskans and Australians [1]–[3]. Although vaccination is the most cost-effective method of protection against pneumococcal disease, cost remains a barrier, as does vaccine delivery and efficacy. In this opinion piece, we discuss the potential complementary role of probiotics to vaccines in preventing pneumococcal disease through targeting the microbiome of the upper respiratory tract.
Public Library of Science
Journals
2012 EN
Didier Hocquet · Catherine Llanes · Michelle Thouverez
+5 more
Bacterial resistance to β-lactams may rely on acquired β-lactamases encoded by class 1 integron-borne genes. Rearrangement of integron cassette arrays is mediated by the integrase IntI1. It has been previously established that integrase expression can be activated by the SOS response in vitro , leading to speculation that this is an important clinical mechanism of acquiring resistance. Here we report the first in vivo evidence of the impact of SOS response activated by the antibiotic treatment given to a patient and its output in terms of resistance development. We identified a new mechanism of modulation of antibiotic resistance in integrons, based on the insertion of a genetic element, the gcuF1 cassette, upstream of the integron-borne cassette bla OXA-28 encoding an extended spectrum β-lactamase. This insertion creates the fused protein GCUF1-OXA-28 and modulates the transcription, the translation, and the secretion of the β-lactamase in a Pseudomonas aeruginosa isolate (S- Pae ) susceptible to the third generation cephalosporin ceftazidime. We found that the metronidazole, not an anti-pseudomonal antibiotic given to the first patient infected with S- Pae , triggered the SOS response that subsequently activated the integrase IntI1 expression. This resulted in the rearrangement of the integron gene cassette array, through excision of the gcuF1 cassette, and the full expression the β-lactamase in an isolate (R- Pae ) highly resistant to ceftazidime, which further spread to other patients within our hospital. Our results demonstrate that in human hosts, the antibiotic-induced SOS response in pathogens could play a pivotal role in adaptation process of the bacteria.
Public Library of Science
Journals
2012 EN
Gabriele Neumann · Catherine A. Macken · Alexander I. Karasin
+2 more
Highly pathogenic avian H5N1 influenza viruses are now enzootic in parts of Southeast Asia and the Middle East. Occasionally, these viruses transmit to humans and cause severe respiratory disease and fatalities. Currently, these viruses are not efficiently transmitted from person to person, although limited human-to-human transmission may have occurred [1]–[4]. A major determinant of influenza virus host range is the viral hemagglutinin (HA) protein: avian virus HA binds preferentially to sialic acid linked to the penultimate galactose residue by an α2,3-linkage (Siaα2,3Gal) [5]–[7], as found for sialic acid–containing receptors of the epithelial cells in duck intestine [8], the site of avian influenza virus replication. By contrast, human virus HA has higher affinity for Siaα2,6Gal [5]–[7], the main sialyloligosaccharide on the epithelial cells of the human upper respiratory tract [9], [10].
Public Library of Science
Journals
2012 EN
Armand PerretLiaudet · Mathieu Pelpel · Yannick Tholance
+15 more
International audienc
American Association for Clinical Chemistry
Journals
2012 EN
Mathew P. Estey · Eleftherios P. Diamandis · Catherine Van Der Straeten
+3 more
Approximately 1 million metal-on-metal (MoM)6 hip prostheses have been implanted worldwide to alleviate pain, restore hip function, and improve overall quality of life. These implants contain femoral and acetabular bearing surfaces that are typically composed predominantly of cobalt (Co) and chromium (Cr). Although the majority of MoM hip replacements have been successful, multiple recent reports have documented markedly increased Co and Cr concentrations in the joint synovial fluid, periprosthetic tissue, blood, and even peripheral tissues of some patients with MoM hip prostheses. Consequently, concerns have been raised about the physiological consequences of metal release from MoM hip prostheses into the periprosthetic tissue and systemic circulation.Co and Cr concentrations in the serum and hip joint fluid correlate with the degree of MoM implant wear and are increased in individuals with an accumulation of metal debris in the periprosthetic tissue. Therefore, some scientists have suggested that Co and Cr concentrations be routinely measured during the management of patients with MoM hip prostheses. In this Q&A article, 4 experts provide their opinions on the use of MoM hip prostheses, the adverse biological consequences of metal release, and the clinical utility of Co and Cr measurements. They also discuss the methodology used to assess the concentration of these metal ions and provide insight into the many challenges associated with Co and Cr measurement.What are the advantages of MoM hip prostheses over other types of implants? Catherine Van Der Straeten: MoM was reintroduced as a bearing surface for hip arthroplasty to solve the problem of particle-induced osteolysis secondary to polyethylene wear. In vitro hip-simulator studies demonstrated much less volumetric wear and much smaller particles with MoM compared to metal-on-polyethylene (MoP). This finding was confirmed in vivo with high-carbon alloy MoM 28-mm and 32-mm total hip arthroplasty (THA). The use of larger-diameter femoral …
American Association for Clinical Chemistry