Effects of experimental harvesting on recruitment of an alien mussel Mytilus galloprovincialis

Successful fisheries management is underpinned by an understanding of the processes that underlie the population dynamics of exploited stocks. This study considered the effects of experimental harvesting on recruitment of Mytilus galloprovincialis along the west coast of South Africa, where harvesting of this alien species is being contemplated. In particular, the role of settlement habitat availability in the form of adult mussels was analysed. To track the effects of a spectrum of harvesting intensities, five treatments were implemented: F = 0 (i.e. a control), F = 0.3, F = 0.6, F = 0.9 and F = 1. At these harvesting intensities 0%, 30%, 60%, 90% or 100% of mussel biomass was removed respectively at the outset of the experiment. A significant negative exponential relationship (p < 0.01) was found between M. galloprovincialis recruit density and harvesting intensity, with intensities greater than F = 0.3 dramatically reducing recruitment. This pattern was recorded throughout the intertidal zone and remained temporally constant over 2 years. Significant positive linear relationships (p < 0.01) between recruit density and adult mussel biomass or density indicate a strong correlation between availability of settlement habitat and recruitment. It is likely that the high recruit density recorded at low harvesting intensities (2000-20 000 per 0.01 m²) exceeds the level required for population maintenance. However, if settlement habitat is eliminated or significantly reduced, as was achieved by F = 0.3 or above, recruitment may become limiting. Thus, to protect stock replenishment, harvesting of M. galloprovincialis in this region should take place at intensities less than F = 0.3.     

Novel wine-mediated FLO11 flocculation phenotype of commercial Saccharomyces cerevisiae wine yeast strains with modified FLO gene expression

Depending on the genetic background of Saccharomyces strains, a wide range of phenotypic adhesion identities can be directly attributed to the FLO11-encoded glycoprotein, which includes asexual flocculation, invasive growth and pseudohyphal formation, flor formation and adhesion to biotic and abiotic surfaces. In a previous study, we reported that HSP30-mediated stationary-phase expression of the native chromosomal FLO11 ORF in two nonflocculent commercial Saccharomyces cerevisiae wine yeast strains, BM45 or VIN13 did not generate a flocculent phenotype under either standard laboratory media or synthetic MS300 must fermentation conditions. In the present study, the BM45- and VIN13-derived HSP30p-FLO11 wine yeast transformants were observed to be exclusively and strongly flocculent under authentic red wine-making conditions, thus suggesting that this specific fermentation environment specifically contributes to the development of a flocculent phenotype, which is insensitive to either glucose or mannose. Furthermore, irrespective of the strain involved this phenotype displayed both Ca(2+)-dependent and Ca(2+)-independent flocculation characteristics. A distinct advantage of this unique FLO11-based phenotype was highlighted in its ability to dramatically promote faster lees settling rates. Moreover, wines produced by BM45-F11H and VIN13-F11H transformants were significantly less turbid than those produced by their wild-type parental strains.     

Dehalogenase gene detection and microbial diversity of a chlorinated hydrocarbon contaminated site

In recent years large quantities of mixtures of chlorinated hydrocarbons have accumulated in the environment due to the widespread use and production of these compounds. Microbes have been found to demonstrate a widespread and diverse potential to adapt to the dechlorination of such compounds. Therefore the aim of this study was to investigate the presence and diversity of reductive and hydrolytic dehalogenase genes in a site contaminated with a mixture of chlorinated hydrocarbons. Primers targeting reductive and hydrolytic bacterial dehalogenase genes were designed. In addition, DGGE analysis was performed in order to determine the presence of any known dehalogenase-producing organisms. Total DNA isolated from borehole water samples was used as the template for the amplification reactions. All PCR products obtained with the reductive and hydrolytic gene primers, as well as the dominant bands present on the DGGE gel were cloned and sequenced. Sequencing of the individual amplicons revealed significant identities to the tceA gene of Dehalococcoides ethenogenes 195, the vcrA gene of Dehalococcoides sp. VS as well as the dhlA and dhlB genes of Xanthobacter autotrophicus GJ10. DGGE analysis indicated a high level of commonality with the different sampling times and depths. However, sequence analysis revealed that 66% of the cloned fragments showed significant (95–99%) identity with uncultured microorganisms. Phylogenetic analysis of the sequences revealed that the DGGE clones clustered into two groups when compared to known bacteria having hydrocarbon degradative capabilities. This indicated that the sequences of the clones were diverse when compared to known microorganisms. This diversity represents a largely untapped genetic pool that can be exploited for the discovery of novel biocatalysts that can be employed in bioremediation. In addition, the presence of both hydrolytic and reductive dehalogenases provided strong evidence that bacteria capable of dehalogenation of chlorinated hydrocarbons may be present in sites contaminated with these compounds.     

A molecular assay for sensitive detection of pathogen-specific T-cells

Here we describe the development and validation of a highly sensitive assay of antigen-specific IFN-γ production using real time quantitative PCR (qPCR) for two reporters--monokine-induced by IFN-γ (MIG) and the IFN-γ inducible protein-10 (IP10). We developed and validated the assay and applied it to the detection of CMV, HIV and Mycobacterium tuberculosis (MTB) specific responses, in a cohort of HIV co-infected patients. We compared the sensitivity of this assay to that of the ex vivo RD1 (ESAT-6 and CFP-10)-specific IFN-γ Elispot assay. We observed a clear quantitative correlation between the two assays (P<0.001). Our assay proved to be a sensitive assay for the detection of MTB-specific T cells, could be performed on whole blood samples of fingerprick (50 uL) volumes, and was not affected by HIV-mediated immunosuppression. This assay platform is potentially of utility in diagnosis of infection in this and other clinical settings.     

Evidence that the human pathogenic fungus Cryptococcus neoformans var. grubii may have evolved in Africa

Most of the species of fungi that cause disease in mammals, including Cryptococcus neoformans var. grubii (serotype A), are exogenous and non-contagious. Cryptococcus neoformans var. grubii is associated worldwide with avian and arboreal habitats. This airborne, opportunistic pathogen is profoundly neurotropic and the leading cause of fungal meningitis. Patients with HIV/AIDS have been ravaged by cryptococcosis--an estimated one million new cases occur each year, and mortality approaches 50%. Using phylogenetic and population genetic analyses, we present evidence that C. neoformans var. grubii may have evolved from a diverse population in southern Africa. Our ecological studies support the hypothesis that a few of these strains acquired a new environmental reservoir, the excreta of feral pigeons (Columba livia), and were globally dispersed by the migration of birds and humans. This investigation also discovered a novel arboreal reservoir for highly diverse strains of C. neoformans var. grubii that are restricted to southern Africa, the mopane tree (Colophospermum mopane). This finding may have significant public health implications because these primal strains have optimal potential for evolution and because mopane trees contribute to the local economy as a source of timber, folkloric remedies and the edible mopane worm.     

Two different hydrogenase enzymes from sulphate-reducing bacteria are responsible for the bioreductive mechanism of platinum into nanoparticles

A mixed consortium of sulphate-reducing bacteria was used to investigate the enzymatic mechanism for the total bioreduction of platinum (IV) into platinum (0) nanoparticles. It was established that two different hydrogenase enzymes were involved. First the platinum (IV) was reduced to platinum (II) by a two-electron bioreduction using an oxygen-sensitive novel cytoplasmic hydrogenase. Second the platinum (II) ion was reduced to platinum (0) nanoparticle by another two-electron bioreduction involving an oxygen-tolerant/protected periplasmic hydrogenase. The enzyme was identified from its reaction with Cu(II), an active inhibitor of periplasmic hydrogenases. No exogenous electron donors were necessary as endogenous production of hydrogen/electrons, via the oxidation of metabolites, was generated in situ by the cytoplasmic hydrogenase. The hydrogen then dispersed through the cell to the periplasm where it became available for use by the periplasmic hydrogenase. The endogenous electrons were used, in the absence of sulphate, for the reduction of platinum (II) by the periplasmic hydrogenase. It was found that the Pt(IV) ion must be fully reduced before reduction of the Pt(II) ion would begin. Transmission electron microscopy and energy dispersive X-ray analysis confirmed the deposit of platinum particles into the periplasmic space.     

Pentacycloundecane derived hydroxy acid peptides: a new class of irreversible non-scissile ether bridged type isoster as potential HIV-1 wild type C-SA protease inhibitors

Novel peptides incorporating the PCU derived hydroxy acid (5-hydroxy-4-oxahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecane) were synthesized and their activity against the resistance-prone wild type C-South African (C-SA) HIV-protease is reported. The attachment of peptides and peptoids to the PCU derived hydroxy acid resulted in a series of structurally diverse promising HIV-1 protease inhibitors. Amongst the nine novel compounds, 16, 17, 20 and 23 gave IC(50) values ranging from 0.6 to 5.0 μM against the wild type C-SA HIV-1 protease enzyme. Docking studies and molecular dynamic (MD) simulations have been carried out in order to understand the binding mode of the PCU moiety at the active site of the HIV protease enzyme. A conserved hydrogen bonding pattern between the PCU derived hydroxy ether and the active site residues, ASP25/ASP25', was observed in all active compounds.