Quorum Sensing Protects Pseudomonas aeruginosa against Cheating by Other Species in a Laboratory Coculture Model

This is the published version. Copyright © 2015, American Society for Microbiology. All Rights Reserved.Many species of bacteria use a cell-cell communication system called quorum sensing (QS) to coordinate group activities. QS systems frequently regulate the production of exoproducts. Some of these products, such as proteases, are “public goods” that are shared among the population and vulnerable to cheating by nonproducing members of the population. Because the QS system of the opportunistic pathogen Pseudomonas aeruginosa regulates several public goods, it can serve as a model for studying cooperation. Bacteria also commonly regulate antimicrobial production through QS. In this study, we focused on the hypothesis that QS-regulated antimicrobials may be important for P. aeruginosa to protect against cheating by another bacterial species, Burkholderia multivorans. We assessed laboratory cocultures of P. aeruginosa and B. multivorans and investigated the importance of three P. aeruginosa QS-regulated antimicrobials, hydrogen cyanide, rhamnolipids, and phenazines, for competition. We found that P. aeruginosa dominates cocultures with B. multivorans and that the three antimicrobials together promote P. aeruginosa competitiveness, with hydrogen cyanide contributing the greatest effect. We show that these QS-regulated antimicrobials are also critical for P. aeruginosa to prevent B. multivorans from cheating under nutrient conditions where both species require a P. aeruginosa quorum-regulated protease for growth. Together our results highlight the importance of antimicrobials in protecting cooperating populations from exploitation by other species that can act as cheaters

The Pathogenic Properties of a Novel and Conserved Gene Product, KerV, in Proteobacteria

Identification of novel virulence factors is essential for understanding bacterial pathogenesis and designing antibacterial strategies. In this study, we uncover such a factor, termed KerV, in Proteobacteria. Experiments carried out in a variety of eukaryotic host infection models revealed that the virulence of a Pseudomonas aeruginosa kerV null mutant was compromised when it interacted with amoebae, plants, flies, and mice. Bioinformatics analyses indicated that KerV is a hypothetical methyltransferase and is well-conserved across numerous Proteobacteria, including both well-known and emerging pathogens (e.g., virulent Burkholderia, Escherichia, Shigella, Vibrio, Salmonella, Yersinia and Brucella species). Furthermore, among the 197 kerV orthologs analyzed in this study, about 89% reside in a defined genomic neighborhood, which also possesses essential DNA replication and repair genes and detoxification gene. Finally, infection of Drosophila melanogaster with null mutants demonstrated that KerV orthologs are also crucial in Vibrio cholerae and Yersinia pseudotuberculosis pathogenesis. Our findings suggested that KerV has a novel and broad significance as a virulence factor in pathogenic Proteobacteria and it might serve as a new target for antibiotic drug design

Intersection of phosphate transport, oxidative stress and TOR signalling in Candida albicans virulence

Phosphate is an essential macronutrient required for cell growth and division. Pho84 is the major high-affinity cell-surface phosphate importer of Saccharomyces cerevisiae and a crucial element in the phosphate homeostatic system of this model yeast. We found that loss of Candida albicans Pho84 attenuated virulence in Drosophila and murine oropharyngeal and disseminated models of invasive infection, and conferred hypersensitivity to neutrophil killing. Susceptibility of cells lacking Pho84 to neutrophil attack depended on reactive oxygen species (ROS): pho84-/- cells were no more susceptible than wild type C. albicans to neutrophils from a patient with chronic granulomatous disease, or to those whose oxidative burst was pharmacologically inhibited or neutralized. pho84-/- mutants hyperactivated oxidative stress signalling. They accumulated intracellular ROS in the absence of extrinsic oxidative stress, in high as well as low ambient phosphate conditions. ROS accumulation correlated with diminished levels of the unique superoxide dismutase Sod3 in pho84-/- cells, while SOD3 overexpression from a conditional promoter substantially restored these cells’ oxidative stress resistance in vitro. Repression of SOD3 expression sharply increased their oxidative stress hypersensitivity. Neither of these oxidative stress management effects of manipulating SOD3 transcription was observed in PHO84 wild type cells. Sod3 levels were not the only factor driving oxidative stress effects on pho84-/- cells, though, because overexpressing SOD3 did not ameliorate these cells’ hypersensitivity to neutrophil killing ex vivo, indicating Pho84 has further roles in oxidative stress resistance and virulence. Measurement of cellular metal concentrations demonstrated that diminished Sod3 expression was not due to decreased import of its metal cofactor manganese, as predicted from the function of S. cerevisiae Pho84 as a low-affinity manganese transporter. Instead of a role of Pho84 in metal transport, we found its role in TORC1 activation to impact oxidative stress management: overexpression of the TORC1-activating GTPase Gtr1 relieved the Sod3 deficit and ROS excess in pho84-/- null mutant cells, though it did not suppress their hypersensitivity to neutrophil killing or hyphal growth defect. Pharmacologic inhibition of Pho84 by small molecules including the FDA-approved drug foscarnet also induced ROS accumulation. Inhibiting Pho84 could hence support host defenses by sensitizing C. albicans to oxidative stress

Stitching Repair for Delaminated Carbon Fiber/Bismaleimide Composite Laminates

Due to the excellent mechanical properties and heat resistance, bismaleimide matrix composite materials have been widely used in aircraft. However, they are susceptible to low-energy impacts, such as bird hits, gravel, tools falling, etc., which can easily result in delamination. The delamination can significantly reduce the compression performance of composites and become a potential hazard for aircraft in service. In this paper, a stitching method developed from the Z-pin manufacturing process was proposed to repair delaminated laminates. Firstly, the delaminated area was stitched by fiber bundles that were pre-impregnated with glue. Then, the fiber bundles threading through the laminate become the pins after the curing process, thus producing the bridging effect between delaminated layers. As a result, the in-plane compressive properties of the laminate are enhanced. The parameters, including the size, number, and position of the stitching hole, for the stitching repair were optimized, and the factors affecting the repair effect were discussed through both finite element analysis and experiments. The results showed that for a carbon fiber/bismaleimide composite plate with a circular delamination roughly 30 mm in diameter, the in-plane compressive strength can be recovered from 54.45% to 84.23% of the pristine plate, and the modulus was fully recovered

Multifunctional and Recollectable Carbon Nanotube Ponytails for Water Purification

Carbon nanotubes (CNTs) are promising nanomaterials that have the potential to revolutionize water treatment practices in the future. The direct use of unbounded CNTs, however, poses health risks to humans and ecosystems because they are difficult to separate from treated water. Here, we report the design and synthesis of carbon nanotube ponytails (CNPs) by integrating CNTs into micrometer-sized colloidal particles, which greatly improves the effectiveness of post-treatment separation using gravitational sedimentation, magnetic attraction, and membrane filtration. We further demonstrate that CNPs can effectively perform major treatment tasks including adsorption, disinfection, and catalysis. Using model pollutants such as methylene blue, <i>Escherichia coli</i>, and <i>p</i>-nitrophenol, we show that all the surfaces of individual CNTs in CNPs are accessible during water treatment. Our results suggest that the rational design of hierarchical structures represents a feasible approach to develop nanomaterials for engineering applications such as water and wastewater treatment

Sphingolipids from a symbiotic microbe regulate homeostasis of host intestinal natural killer T cells

SummaryCoevolution of beneficial microorganisms with the mammalian intestine fundamentally shapes mammalian physiology. Here, we report that the intestinal microbe Bacteroides fragilis modifies the homeostasis of host invariant natural killer T (iNKT) cells by supplementing the host’s endogenous lipid antigen milieu with unique inhibitory sphingolipids. The process occurs early in life and effectively impedes iNKT cell proliferation during neonatal development. Consequently, total colonic iNKT cell numbers are restricted into adulthood, and hosts are protected against experimental iNKT cell-mediated, oxazolone-induced colitis. In studies with neonatal mice lacking access to bacterial sphingolipids, we found that treatment with B. fragilis glycosphingolipids—exemplified by an isolated peak (MW = 717.6) called GSL-Bf717—reduces colonic iNKT cell numbers and confers protection against oxazolone-induced colitis in adulthood. Our results suggest that the distinctive inhibitory capacity of GSL-Bf717 and similar molecules may prove useful in the treatment of autoimmune and allergic disorders in which iNKT cell activation is destructive.PaperCli