Heteroresistance to the model antimicrobial peptide polymyxin B in the emerging Neisseria meningitidis lineage 11.2 urethritis clade: mutations in the pilMNOPQ operon

Clusters of Neisseria meningitidis (Nm) urethritis among primarily heterosexual males in multiple US cities have been attributed to a unique non‐encapsulated meningococcal clade (the US Nm urethritis clade, US_NmUC) within the hypervirulent clonal complex 11. Resistance to antimicrobial peptides (AMPs) is a key feature of urogenital pathogenesis of the closely related species, Neisseria gonorrhoeae. The US_NmUC isolates were found to be highly resistant to the model AMP, polymyxin B (PmB, MICs 64–256 µg ml^–1). The isolates also demonstrated stable subpopulations of heteroresistant colonies that showed near total resistant to PmB (MICs 384–1024 µg ml^–1) and colistin (MIC 256 µg ml^–1) as well as enhanced LL‐37 resistance. This is the first observation of heteroresistance in N. meningitidis. Consistent with previous findings, overall PmB resistance in US_NmUC isolates was due to active Mtr efflux and LptA‐mediated lipid A modification. However, whole genome sequencing, variant analyses and directed mutagenesis revealed that the heteroresistance phenotypes and very high‐level AMP resistance were the result of point mutations and IS1655 element movement in the pilMNOPQ operon, encoding the type IV pilin biogenesis apparatus. Cross‐resistance to other classes of antibiotics was also observed in the heteroresistant colonies. High‐level resistance to AMPs may contribute to the pathogenesis of US_NmUC.     

The limits to population density in birds and mammals

We address two fundamental ecological questions: what are the limits to animal population density and what determines those limits? We develop simple alternative models to predict population limits in relation to body mass. A model assuming that within‐species area use increases with the square of daily travel distance broadly predicts the scaling of empirical extremes of minimum density across birds and mammals. Consistent with model predictions, the estimated density range for a given mass, ‘population scope’, is greater for birds than for mammals. However, unlike mammals and carnivorous birds, expected broad relationships between body mass and density extremes are not supported by data on herbivorous and omnivorous birds. Our results suggest that simple constraints on mobility and energy use/supply are major determinants of the scaling of density limits, but further understanding of interactions between dietary constraints and density limits are needed to predict future wildlife population responses to anthropogenic threats.     

Expansion of Bacteriophages Is Linked to Aggravated Intestinal Inflammation and Colitis

1. Download high-res image (192KB)
2. Download full-size image

     

Structure elucidation of arabinoxylan isomers by normal phase HPLC-MALDI-TOF/TOF-MS/MS

Normal phase-high performance liquid chromatography (NP-HPLC) coupled to matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight (MALDI-TOF/TOF) tandem mass spectrometry is evaluated for the detailed structural characterization of various isomers of arabinoxylan (AX) oligosaccharides produced from endo-beta-(1-->4)-xylanase (endoxylanase) digestion of wheat AX. The fragmentation characteristics of these oligosaccharides upon MALDI-TOF/TOF high-energy collision induced dissociation (CID) were investigated using purified AX oligosaccharide standards labeled at the reducing end with 2-aminobenzoic acid (2-AA). A variety of cross-ring cleavages and 'elimination' ions in the fragment ion spectra provided extensive structural information, including Araf substitution patterns along the xylan backbone and comprehensive linkage assignment. The off-line coupling of this MALDI-CID technique to capillary normal phase HPLC enabled the separation and identification of isomeric oligosaccharides (DP 4-8) produced by endoxylanase digestion of AX. Furthermore, this technique was used to characterize structurally different isomeric AX oligosaccharides produced by endoxylanase enzymes with different substrate specificities.     

Fast and accurate estimation of the population-scaled mutation rate, theta, from microsatellite genotype data

We present a new approach for estimation of the population-scaled mutation rate, , from microsatellite genotype data, using the recently introduced "product of approximate conditionals" framework. Comparisons with other methods on simulated data demonstrate that this new approach is attractive in terms of both accuracy and speed of computation. Our simulation experiments also demonstrate that, despite the theoretical advantages of full-likelihood-based methods, methods based on certain summary statistics (specifically, the sample homozygosity) can perform very competitively in practice.     

Whole community estimates of macroalgal pigment concentration within two southern New Zealand kelp forests1

Light availability is a fundamental factor that controls the productivity and distribution of macroalgae and is highly variable, both spatially and temporally, in subtidal coastal systems. Our comprehension of how macroalgae respond to such variability is a significant knowledge gap that limits our understanding of how light influences the structure and productivity of these environments. Here, we examined the pigment characteristics of individual species, and for the first time the whole community, within one low‐light, and one high‐light kelp‐forest system in southern New Zealand. The aim was to quantify the range of pigmentation seen within the two kelp‐forests which differed in irradiance regime. Light availability was 33% and 64% greater at the high‐light compared to the low‐light site at 2 and 10 m depth, respectively. Results suggested Phaeophyceae species at deeper depths in the low‐light site may be living at the edge of their photosynthetic ability and pigment synthesis appeared significantly restricted. Even with greater investment in the pigment fucoxanthin, biomass of Phaeophyceae species was significantly lower in the low‐light site. Highly pigmented Rhodophyceae species made a greater proportional contribution to community biomass within the low‐light site where they likely possessed a photosynthetic advantage. This work helps explain discrepancies in community structure between the two study sites and explores the complex relationship between irradiance and photoacclimation. The comparison of community pigment concentration holds potential as a tool for assessing the relative degree of photoacclimation occurring between sites and provides a proxy of photosynthetic cost under a specific light regime.     

Src family kinases mediate receptor-stimulated, phosphoinositide 3-kinase-dependent, tyrosine phosphorylation of dual adaptor for phosphotyrosine and 3-phosphoinositides-1 in endothelial and B cell lines

DAPP-1 (dual-adaptor for phosphotyrosine and 3-phosphoinositides-1) is a broadly distributed pleckstrin homology (PH) and Src homology 2 domain containing protein that can bind phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) and can be phosphorylated on tyrosine 139 and internalised in response to activation of type I phosphoinositide 3-kinases (PI3K). Tyrosine phosphorylation of DAPP-1 appears important for appropriate intracellular targeting and creates a potential binding site for Src homology 2 domain-containing proteins. In endothelial cells overexpressing wild-type platelet-derived growth factor beta (PDGFbeta) receptors, which express Bmx and Src as their major Btk (Bruton's tyrosine kinase) family and Src family tyrosine kinases, respectively, PDGF can stimulate PI3K-dependent tyrosine phosphorylation of DAPP-1. Transient overexpression of Src most effectively, compared with Bmx and Syk, augments basal and PDGF-stimulated tyrosine phosphorylation of DAPP-1, whereas overexpression of dominant-negative Src, but not dominant-negative Bmx, inhibits PDGF-stimulated phosphorylation of DAPP-1. Cells expressing mutant PDGFbeta (Y579F/Y581F) receptors (which fail to bind and activate Src-type kinases) fail to tyrosine phosphorylate DAPP-1 in response to PDGF. We show that in DT40 chicken B cell lines, antibody stimulation leads to PI3K-dependent tyrosine phosphorylation of DAPP-1 that is lost in Lyn- or Syk-deficient cell lines but not Btk-deficient cell lines. PI3K-dependent activation of PKB is only lost in Syk-deficient lines. Finally, in vitro we find lipid-modified Src to be the most effective DAPP-1 tyrosine kinase (versus Syk, Lyn, Btk, and Bmx); phosphorylation of DAPP-1 but not Src autophosphorylation is stimulated approximately 10-fold by PtdIns(3,4,5)P(3) (IC(50) = 150 nm) and phosphatidylinositol 3,4-bisphosphate but not by their nonbiological diastereoisomers and depends on PH domain mediated binding of DAPP-1 to PtdIns(3,4,5)P(3)-containing membranes. We conclude that Src family kinases are responsible for tyrosine phosphorylation of DAPP-1 in vivo and that PI3K regulation is at the level of PH domain-mediated translocation of DAPP-1 to PI3K products in the membrane.     

Haliotrema abaddon n. sp. (Monogenoidea: Dactylogyridae) from the gills of wild and maricultured West Australian dhufish Glaucosoma hebraicum (teleostei: Glaucosomatidae), in Australia

Haliotrema abaddon n. sp. (Dactylogyridae) is described from the gills of West Australian dhufish Glaucosoma hebraicum (Teleostei: Glaucosomatidae), from the Indian Ocean near Fremantle, Western Australia. The parasite is recorded from cultured dhufish and from a major portion of the known geographic distribution of its host. In cultured dhufish, H. abaddon causes branchitis and hyperplasia and metaplasia of the lamellar epithelial cells and may be a limiting factor in the development of an economically feasible mariculture industry. Comparable prevalences and densities of the parasite on wild and cultured dhufish were observed. In heavily infested captive fish, clusters of eggs (egg strands) appear to restrict blood flow to localized regions of the gills as a result of entanglement of egg filaments with secondary gill lamellae. Hatching of oncomiracidia occurs in 7-10 days at 20-25 C.