Acquisition of ionic copper by the bacterial outer membrane protein OprC through a novel binding site

Copper, while toxic in excess, is an essential micronutrient in all kingdoms of life due to its essential role in the structure and function of many proteins. Proteins mediating ionic copper import have been characterised in detail for eukaryotes, but much less so for prokaryotes. In particular, it is still unclear whether and how gram-negative bacteria acquire ionic copper. Here, we show that Pseudomonas aeruginosa OprC is an outer membrane, TonB-dependent transporter that is conserved in many Proteobacteria and which mediates acquisition of both reduced and oxidised ionic copper via an unprecedented CxxxM-HxM metal binding site. Crystal structures of wild-type and mutant OprC variants with silver and copper suggest that acquisition of Cu(I) occurs via a surface-exposed “methionine track” leading towards the principal metal binding site. Together with whole-cell copper quantitation and quantitative proteomics in a murine lung infection model, our data identify OprC as an abundant component of bacterial copper biology that may enable copper acquisition under a wide range of conditions.

How do Gram-negative bacteria acquire copper? This study shows that the outer membrane protein OprC from Pseudomonas aeruginosa is abundant during infection and mediates highly selective acquisition of both copper redox states via an extracellular "methionine track" and an unprecedented near-irreversible binding site.     

Social and reproductive conditions modulate urinary cortisol excretion in black tufted-ear marmosets (Callithrix kuhli)

The links between psychosocial stress, social status, reproductive function, and urinary cortisol were assessed in social groups of black tufted-ear marmosets (Callithrix kuhli). Urinary cortisol excretion was monitored in cases of intrafamily conflict (“sibling fights”) and in daughters in four distinct social contexts: in the family group, while housed singly or in same-sex pairs, and while paired with a male pairmate. Cortisol excretion was elevated in participants in intra-family conflict on the day of and the day following the conflict, relative to concentrations a week prior to or following the conflict. Daughters in natal family groups had concentrations of cortisol that did not differ from reproductively active adult females. This finding held for daughters who were either anovulatory or undergoing ovulatory cycles while in the natal family group. Natal family members and male pairmates exerted buffering effects on levels of activity in the hypothalamic pituitary adrenal axis (HPA) in female C. kuhli. Placing females in solitary housing led to significantly increased cortisol excretion. In the 2 months subsequent to pairing with a male partner, excreted cortisol concentrations in females declined significantly. Daughters removed from their natal family group and housed with a sister did not exhibit increased cortisol levels. These data reveal that activity in the (HPA) axis in marmosets is sensitive to psychosocial stressors, and that urinary cortisol can provide a useful quantitative measure of HPA reactivity. As in other callitrichids, delayed breeding in daughters and reproductive anomalies in C. kuhli appear to be mediated by mechanisms other than elevated HPA activity. Am. J. Primatol. 42:253–267, 1997. © 1997 Wiley-Liss, Inc.     

Interspecific hybridization causes long‐term phylogenetic discordance between nuclear and mitochondrial genomes in freshwater fishes

Classification, phylogeography and the testing of evolutionary hypotheses rely on correct estimation of species phylogeny. Early molecular phylogenies often relied on mtDNA alone, which acts as a single linkage group with one history. Over the last decade, the use of multiple nuclear sequences has often revealed conflict among gene trees. This observation can be attributed to hybridization, lineage sorting, paralogy or selection. Here, we use 54 groups of fishes from 48 studies to estimate the degree of concordance between mitochondrial and nuclear gene trees in two ecological grades of fishes: marine and freshwater. We test the hypothesis that freshwater fish phylogenies should, on average, show more discordance because of their higher propensity for hybridization in the past. In keeping with this idea, concordance between mitochondrial and nuclear gene trees (as measured by proportion of components shared) is on average 50% higher in marine fishes. We discuss why this difference almost certainly results from introgression caused by greater historical hybridization among lineages in freshwater groups, and further emphasize the need to use multiple nuclear genes, and identify conflict among them, in estimation of species phylogeny.     

Coral reef mesopredators switch prey,shortening food chains,in response to habitat degradation

Diet specificity is likely to be the key predictor of a predator's vulnerability to changing habitat and prey conditions. Understanding the degree to which predatory coral reef fishes adjust or maintain prey choice, in response to declines in coral cover and changes in prey availability, is critical for predicting how they may respond to reef habitat degradation. Here, we use stable isotope analyses to characterize the trophic structure of predator–prey interactions on coral reefs of the Keppel Island Group on the southern Great Barrier Reef, Australia. These reefs, previously typified by exceptionally high coral cover, have recently lost much of their coral cover due to coral bleaching and frequent inundation by sediment‐laden, freshwater flood plumes associated with increased rainfall patterns. Long‐term monitoring of these reefs demonstrates that, as coral cover declined, there has been a decrease in prey biomass, and a shift in dominant prey species from pelagic plankton‐feeding damselfishes to territorial benthic algal‐feeding damselfishes, resulting in differences in the principal carbon pathways in the food web. Using isotopes, we tested whether this changing prey availability could be detected in the diet of a mesopredator (coral grouper, Plectropomus maculatus). The δ¹³C signature in grouper tissue in the Keppel Islands shifted from a more pelagic to a more benthic signal, demonstrating a change in carbon sources aligning with the change in prey availability due to habitat degradation. Grouper with a more benthic carbon signature were also feeding at a lower trophic level, indicating a shortening in food chains. Further, we found a decline in the coral grouper population accompanying a decrease in total available prey biomass. Thus, while the ability to adapt diets could ameliorate the short‐term impacts of habitat degradation on mesopredators, long‐term effects may negatively impact mesopredator populations and alter the trophic structure of coral reef food webs.     

Social correlates of testosterone and ornamentation in male mandrills

We investigated relationships between fecal androgen concentrations, facial coloration and behaviour in semi-free-ranging male mandrills. We found that fecal androgen levels were significantly positively related to dominance rank, independent of rank stability and the mating period, suggesting that male mandrills live in a permanently aggressive context in which they must actively maintain their dominance status. Facial red coloration was also significantly related to both fecal androgen levels and rank, with high ranking males having both higher androgen levels and redder faces, although dominant males did not always have the highest androgen levels or the reddest faces. Predictive relationships between androgen levels, coloration and rank were short-term. Androgen concentrations and facial redness both increased in the presence of receptive females, as did the former during periods of rank instability. We conclude that male facial redness is likely to represent an honest signal (to other males) of current androgen status, competitive ability and willingness to engage in fights and that females may also use this to assess male condition. Further, our findings provide support for the “challenge hypothesis” as originally proposed for birds by Wingfield.     

<Emphasis Type="Italic">Myzostoma fuscomaculatum</Emphasis> (Myzostomida), a new myzostome species from False Bay,South Africa

A new myzostome species, described here as Myzostoma fuscomaculatum n. sp. was collected on Tropiometra carinata in False Bay (South Africa), during a survey of symbionts associated with comatulid crinoid species. M. fuscomaculatum n. sp. occurred only on T. carinata and not on the more common crinoid, Comanthus wahlbergi. It infested 61.7% of the 120 host specimens collected, of which 64.9% (48 specimens) hosted more than one individual (maximum of 32). M. fuscomaculatum n. sp. was always located on the host’s arms and pinnules and was cryptically coloured, closely matching the colour pattern of the host. This is the first record of myzostomes from the cool temperate waters of South Africa’s Atlantic coast. The new species is morphologically close to M. gopalai Subramaniam, 1938, collected on T. encrinus in Madras Harbour. M. fuscomaculatum n. sp. differs from M. gopalai in lacking marginal cirri at the adult stage, the presence of three pairs of digestive diverticula, by the position of its lateral organs and by the shape of the manubrium. Molecular phylogenetic analyses based on 18S and 16S rDNA placed M. fuscomaculatum n. sp. into a clade including Hypomyzostoma, Myzostoma and Mesomyzostoma species. Handling editor: K. Martens Déborah Lanterbecq and Tessa Hempson contributed equally to this work.     

Fatal Chytridiomycosis in the Tyrrhenian Painted Frog

Batrachochytrium dendrobatidis (Bd), the causative agent of the amphibian disease chytridiomycosis, is an important factor in the global decline of amphibians. Within Europe, animals that exhibit clinical signs of the disease have only been reported in Spain despite the pathogen’s wide, but patchy, distribution on the continent. Recently, another occurrence of chytridiomycosis was reported in Euproctus platycephalus, the Sardinian brook newt, on the Mediterranean island of Sardinia, but without any evidence of fatal disease. We report further evidence of the emergence of Bd on Sardinia and the first evidence of lethal chytridiomycosis outside of Spain. Unusual mortalities of the Tyrrhenian painted frog (Discoglossus sardus) were found at three sites in the Limbara mountains of northern Sardinia. Molecular and histological screens of corpses, frogs, and tadpoles from these sites revealed infection with Bd. Infection and mortality occurred at locations that are unusual in terms of the published habitat requirements of the pathogen. Given the endemicity, the IUCN Red List status of the amphibian species on Sardinia, and the occurrence of infection and mortality caused by chytridiomycosis, there is serious reason for concern for the impact that disease emergence may have on the conservation of the amphibians of the island.     

Insights in to the pathogenesis of axial spondyloarthropathy based on gene expression profiles

Introduction  

Axial spondyloarthropathy (SpA) is a group of inflammatory diseases, with ankylosing spondylitis as the prototype. SpA affects the axial skeleton, entheses, joints and, at times, the eyes. This study tested the hypothesis that SpA is characterized by a distinct pattern of gene expression in peripheral blood of affected individuals compared with healthy controls.     

A new chemical tool for exploring the role of the PDE4D isozyme in leukocyte function

Nicotinamide (2) is a potent and selective inhibitor of the PDE4D isozyme and as a chemical tool selectively blocks eosinophil mediator release and chemotaxis thus linking the role of PDE4D to eosinophil function.