Molecular characterization of the clumping factor (fibrinogen receptor) of Staphylococcus aureus

Four mutants of Staphylococcus aureus strain Newman that were defective in the fibrinogen receptor (clumping factor) were isolated by transposon Tn917 mutagenesis. Southern hybridization analysis of the mutants identified transposon-host DNA junction fragments, one of which was cloned and used to generate a probe to identify and clone the wild-type clumping factor locus (clfA). The mutants failed to form clumps in soluble fibrinogen and adhered poorly to polymethylmethacrylate (PMMA) coverslips coated with fibrinogen. A single copy of the clfA gene, when introduced into the chromosome of the mutant strains, fuily compiemented the ciumping deficiency of these strains and restored the ability of these mutants to adhere to fibrinogen-coated PMMA. in addition, the cloned clfA gene on a shuttle plasmid aiiowed the weakiy ciumping strain 8325-4 to form clumps with the same avidity as the wild-type strain Newman and also significantly enhanced the adherence of 8325-4 strains. Thus the formation of clumps in soluble fibrinogen correlated with adherence of bacteria to solid-phase fibrinogen. The clfA gene encodes a fibrinogen-binding protein with an apparent molecular mass of c. 130 kDa. The amino acid sequence of the protein was deduced from the DNA sequence; it was predicted that a 896 residue protein (molecular mass 92 kDa) would be expressed. The putative ClfA protein has features that suggest that it is associated with the ceil surface. Furthermore it contains a novel 308 residue region comprising dipeptide repeats predominantly of Asp and Ser ending 28 residues upstream from the LPXTG motif common to wall-associated proteins. Significant homology was found between the ClfA protein and the fibronectin-binding proteins of S. S. aureus, particularly in the N-and C-termini.     

Impact of disease frequency and host density on pollination and transmission of an African anther-smut fungus

The vast majority of flowering plants rely solely on insects for pollination. A number of pathogens have evolved mechanisms to exploit these close associations and use pollinators as vectors of infective propagules. Factors that affect pollinator movements and successful pollination may in turn also influence successful transmission of fungal spores. Here we investigate the effect of host density and the frequency of diseased Oxalis lanata individuals infected by the anther-smut fungus, Thecaphora capensis, on the likelihood of receiving pollen and fungal spores. Specifically, we determined the numbers of spores and pollen grains deposited on stigmatic surfaces of selected flowers under natural and standardized conditions where host density and disease frequency varied. The effect of host flower density and diseased flower frequency on pollen and spore transfer was variable under natural conditions and these factors interacted significantly. However, an increase in host density and disease frequency significantly influenced pollen and spore deposits under standardized conditions. The effect of host density was, however, not linear and an optimal flower density for pollen and fungal spore transmission was found. Similar to other systems of vector-borne disease, the transmission of anther-smut of Oxalis lanata is more frequency-dependent than density-dependent. This study represents a first step towards understanding the disease transmission process of T. capensis on Oxalis and lays the foundation for future comparative studies between this and other systems to develop and test general hypotheses of disease dynamics in vector-borne disease transmission systems.     

Individual tree context and contrast dictate tree physiological features and arthropod biodiversity patterns across multiple trophic levels

1. The present study tested the hypothesis that tree context (natural, semi-natural or planted) and contrast (height of surrounding vegetation) affect tree physiological characters (leaf size, nutrient content, and stress-related factors), and also alter the arthropod biodiversity patterns either directly or indirectly. 2. Arthropods were collected from tree canopies using chemical fogging from the ecologically important South African native tree Podocarpus elongatus. 3. Low contrast trees had significantly larger leaves than those in high contrast environments and harboured an overall higher richness, abundance, and biomass of arthropods, although this was guild-dependent. 4. Trees in natural contexts had less foliar δ¹³C, suffered less from artificial nitrogen enrichment, and harboured significantly higher herbivore and predator arthropod richness and unique assemblages, compared with planted trees. 5. Semi-natural trees supported natural levels of arthropod richness, although these were mostly generalist species. 6. Tree context and contrast can therefore dictate associated biota at multiple trophic levels and native trees may fail to maintain natural biodiversity in transformed landscapes.     

Multiple Bacteriocin Production by Leuconostoc mesenteroidesTA33a and Other Leuconostoc/Weissella Strains

Leuconostoc (Lc.) mesenteroides TA33a produced three bacteriocins with different inhibitory activity spectra. Bacteriocins were purified by adsorption/desorption from producer cells and reverse phase high-performance liquid chromatography. Leucocin C-TA33a, a novel bacteriocin with a predicted molecular mass of 4598 Da, inhibited Listeria and other lactic acid bacteria (LAB). Leucocin B-TA33a has a predicted molecular mass of 3466 Da, with activity against Leuconostoc/Weissella (W.) strains, and appears similar to mesenterocin 52B and dextranicin 24, while leucocin A-TA33a, which also inhibited Listeria and other LAB strains, is identical to leucocin A-UAL 187. A survey of other known bacteriocin-producing Leuconostoc/Weissella strains for the presence of the three different bacteriocins revealed that production of leucocin A-, B- and C-type bacteriocins was widespread. Lc. carnosum LA54a, W. paramesenteroides LA7a, and Lc. gelidum UAL 187-22 produced all three bacteriocins, whereas W. paramesenteroides OX and Lc. carnosum TA11a produced only leucocin A- and B-type bacteriocins. Received: 11 April 1997 / Accepted: 10 June 1997     

Hypomelanosis of Ito in a girl with plexus papilloma and translocation (X;17)

We describe a de novo constitutional (X;17) (q13;p13) translocation in a girl with the clinical features of hypomelanosis of Ito and plexus papilloma.     

Lesions of the Basal Forebrain Cholinergic System in Mice Disrupt Idiothetic Navigation

Loss of integrity of the basal forebrain cholinergic neurons is a consistent feature of Alzheimer’s disease, and measurement of basal forebrain degeneration by magnetic resonance imaging is emerging as a sensitive diagnostic marker for prodromal disease. It is also known that Alzheimer’s disease patients perform poorly on both real space and computerized cued (allothetic) or uncued (idiothetic) recall navigation tasks. Although the hippocampus is required for allothetic navigation, lesions of this region only mildly affect idiothetic navigation. Here we tested the hypothesis that the cholinergic medial septo-hippocampal circuit is important for idiothetic navigation. Basal forebrain cholinergic neurons were selectively lesioned in mice using the toxin saporin conjugated to a basal forebrain cholinergic neuronal marker, the p75 neurotrophin receptor. Control animals were able to learn and remember spatial information when tested on a modified version of the passive place avoidance test where all extramaze cues were removed, and animals had to rely on idiothetic signals. However, the exploratory behaviour of mice with cholinergic basal forebrain lesions was highly disorganized during this test. By contrast, the lesioned animals performed no differently from controls in tasks involving contextual fear conditioning and spatial working memory (Y maze), and displayed no deficits in potentially confounding behaviours such as motor performance, anxiety, or disturbed sleep/wake cycles. These data suggest that the basal forebrain cholinergic system plays a specific role in idiothetic navigation, a modality that is impaired early in Alzheimer’s disease.