Predation Success By A Plant-Ant Indirectly Favours The Growth And Fitness Of Its Host Myrmecophyte

Mutualisms, or interactions between species that lead to net fitness benefits for each species involved, are stable and ubiquitous in nature mostly due to “byproduct benefits” stemming from the intrinsic traits of one partner that generate an indirect and positive outcome for the other. Here we verify if myrmecotrophy (where plants obtain nutrients from the refuse of their associated ants) can explain the stability of the tripartite association between the myrmecophyte Hirtella physophora, the ant Allomerus decemarticulatus and an Ascomycota fungus. The plant shelters and provides the ants with extrafloral nectar. The ants protect the plant from herbivores and integrate the fungus into the construction of a trap that they use to capture prey; they also provide the fungus and their host plant with nutrients. During a 9-month field study, we over-provisioned experimental ant colonies with insects, enhancing colony fitness (i.e., more winged females were produced). The rate of partial castration of the host plant, previously demonstrated, was not influenced by the experiment. Experimental plants showed higher δ¹⁵N values (confirming myrmecotrophy), plus enhanced vegetative growth (e.g., more leaves produced increased the possibility of lodging ants in leaf pouches) and fitness (i.e., more fruits produced and more flowers that matured into fruit). This study highlights the importance of myrmecotrophy on host plant fitness and the stability of ant-myrmecophyte mutualisms.     

From single‐strand breaks to double‐strand breaks during S‐phase: a new mode of action of the Escherichia coli Cytolethal Distending Toxin

The Cytolethal Distending Toxin (CDT) is a genotoxin produced by several pathogenic bacteria. It is generally admitted that CDT induces double‐strand breaks (DSB) and cell cycle arrest in G2/M‐phase, in an ATM‐dependent manner. Most of these results were obtained at high dose (over 1 μg ml^?1) of CDT and late after treatment (8–24 h). We provide here evidence that the Escherichia coli CDT (EcCDT) – at low dose (50 pg ml^?1 or LD50) and early after treatment (3–6 h) – progressively induces DNA DSB, mostly in S‐phase. DSB formation is related to the single‐strand breaks induction by CDT, converted into DSB during the S‐phase. We also show that homologous recombination is mobilized to these S‐phase‐associated DSB. This model unveils a new mechanism for CDT genotoxicity that may play a role in cells partly deficient in homologous recombination.     

On the physical properties and mechanism of action of arylsulfate sulfohydrolase II from Aspergillus oryzae.

Sedimentation equilibrium studies on arylsulfate sulfohydrolase II (EC 3.1.6.1) from Aspergillus oryzae under nondissociating conditions have resulted in a revised molecular weight of 94,900 ± 7100. Sedimentation equilibrium and gel electrophoresis data collected in the presence of the dissociating agents, urea and sodium dodecylsulfate demonstrate that the native enzyme is composed of two identical subunits as suggested by previous studies employing an irreversible inhibitor.The pH dependencies of the kinetic parameters V and $\text{V}\text{K}{}_{\mathrm{m}}$ for the enzymic hydrolysis of 4-nitrophenyl sulfate indicate that two groups of pK_a 4.7 and 6.0 control the activity of the enzyme. The product inorganic sulfate was shown to be a linear competitive inhibitor of the enzyme at pH 4.0, implying that it is a last released product along the reaction pathway. Inhibition by the phenol product was not observed. Enzymic hydrolysis of 4-nitrophenyl sulfate in ¹⁸O enriched water revealed that one atom of solvent oxygen is incorporated per molecule of inorganic sulfate, which is consistent with a mechanism featuring sulfur-oxygen bond cleavage. Evidence is presented based on stopped-flow kinetics, partitioning experiments in the presence of amine nucleophiles, and ¹⁸O exchange studies that collectively suggest that the breakdown of a covalent sulfuryl enzyme intermediate probably is not the rate-limiting step along the reaction pathway.The substrate specificity of the enzyme was examined by testing a variety of sulfate and phosphate esters as inhibitors of the hydrolysis of 4-nitrophenyl sulfate. The Cbz-l-Phe-l-Tyrosine-O-sulfate methyl ester serves as a substrate for the enzyme. Apparently substrate activity requires an aromatic sulfate ester whose binding is enhanced by incorporating the aromatic moiety in a hydrophobic matrix.     

NMR assignment of actin depolymerizing and dynamics regulatory protein from Leishmania donovani

Leishmania donovani cofilin displays low sequence similarity to other mammalian cofilins and also possesses characteristic activity of its own. Determination of its solution structure would facilitate understanding of the molecular mechanism of actin dynamics regulation in this disease causing pathogen.     

Knowledge,perception and practices of colorectal cancer screening in an ethnically diverse population

Background: Colorectal cancer (CRC) screening improves survival and its success depends on the participation of the at-risk population. Few studies have adequately assessed screening knowledge, perception and participation according to birthplace. This study assesses the knowledge and perception of CRC in an ethnically diverse population, and evaluates the association with screening participation and intention. Identification of specific predictors of screening may aid the development of interventions to improve overall CRC screening. Methods: An interview-based survey, conducted on subjects aged 30–70 years, assessed knowledge and perception towards CRC and screening tests. Primary endpoints were screening participation and intent. Statistical methods used were Chi-square, Mann–Whitney U and logistic regression. Results: A total of 543 subjects (43% males, 53% Australian-born (AB), 63% aged 50 years and above) were recruited. Compared with AB, non-Australian-born (NAB) respondents had poorer knowledge, and NAB background predicted for poorer knowledge independent of sex, education, media and familiarity with CRC patient. Compared with AB respondents aged 50 years and above, NAB respondents had lower screening participation (17.4% vs. 31.8%; P = 0.01), lesser intention (75.8% vs. 90.5%; P < 0.001), and had received fewer doctors’ screening recommendations (16.5% vs. 27.1%; P = 0.04). In multivariate analysis, doctors’ recommendation, media and improved perception independently predicted screening participation; knowledge and media exposure predicted intent. Conclusions: The knowledge of CRC and screening is significantly poorer in the immigrant population. Knowledge predicts for greater screening intent. Therefore, implementing language- and culture-specific educational programs involving medical practitioners and media are necessary to improve CRC screening participation rates.     

Prevention of cardiolipin oxidation and fatty acid cycling as two antioxidant mechanisms of cationic derivatives of plastoquinone (SkQs)

The present state of the art in studies on the mechanisms of antioxidant activities of mitochondria-targeted cationic plastoquinone derivatives (SkQs) is reviewed. Our experiments showed that these compounds can operate as antioxidants in two quite different ways, i.e. (i) by preventing peroxidation of cardiolipin [Antonenko et al., Biochemistry (Moscow) 73 (2008) 1273–1287] and (ii) by fatty acid cycling resulting in mild uncoupling that inhibits the formation of reactive oxygen species (ROS) in mitochondrial State 4 [Severin et al. Proc. Natl. Acad. Sci. USA 107 (2009), 663–668]. The quinol and cationic moieties of SkQ are involved in cases (i) and (ii), respectively. In case (i) SkQH₂ interrupts propagation of chain reactions involved in peroxidation of unsaturated fatty acid residues in cardiolipin, the formed SkQ^? being reduced back to SkQH₂ by heme b_H of complex III in an antimycin-sensitive way. Molecular dynamics simulation showed that there are two stable conformations of SkQ1 with the quinol residue localized near peroxyl radicals at C₉ or C₁₃ of the linoleate residue in cardiolipin. In mechanism (ii), fatty acid cycling mediated by the cationic SkQ moiety is involved. It consists of (a) transmembrane movement of the fatty acid anion/SkQ cation pair and (b) back flows of free SkQ cation and protonated fatty acid. The cycling results in a protonophorous effect that was demonstrated in planar phospholipid membranes and liposomes. In mitochondria, the cycling gives rise to mild uncoupling, thereby decreasing membrane potential and ROS generation coupled to reverse electron transport in the respiratory chain. In yeast cells, dodecyltriphenylphosphonium (С₁₂TPP), the cationic part of SkQ1, induces uncoupling that is mitochondria-targeted since С₁₂TPP is specifically accumulated in mitochondria and increases the H⁺ conductance of their inner membrane. The conductance of the outer cell membrane is not affected by С₁₂TPP.