Search PubMed⌕ Search

Biomedical subjects

W F Vincent

Publications and source records attributed to W F Vincent.

At least 19 recordsLinked to original sources
PubMed2000

Effect of climate change relative to ozone depletion on UV exposure in subarctic lakes.

The effect of stratospheric ozone depletion on increases in ambient levels of solar ultraviolet (UV) radiation in high-latitude regions' has raised concerns about the response of northern ecosystems to environmental change. The concentration of coloured dissolved organic material, which is derived from terrestrial vegetation and acts as a screen for ultraviolet radiation, is low in high-latitude lakes. The underwater light environment in these lakes is therefore likely to be sensitive to small variations in the supply of this material, in addition to the effects of ozone depletion. Here we use fossil diatom assemblages in combination with bio-optical models to estimate the magnitude of past variations in the underwater light regime of a lake at the boreal tree line. We find large shifts in underwater UV-B, UV-A and photosynthetically available radiation associated with changes in the input of coloured dissolved organic material into subarctic lakes during the Holocene. The inferred changes in biological exposure to UV radiation were at least two orders of magnitude greater than those associated with moderate (30%) ozone depletion. Our findings indicate that freshwater ecosystems at present located across vegetation gradients will experience significant shifts in underwater spectral irradiance through the effects of climate change on catchment vegetation and the export of coloured dissolved organic material.

Arctic Regions↗
PubMed2000

Ice shelf microbial ecosystems in the high arctic and implications for life on snowball earth.

The Ward Hunt Ice Shelf (83 degrees N, 74 degrees W) is the largest remaining section of thick (> 10 m) land-fast sea ice along the northern coastline of Ellesmere Island, Canada. Extensive meltwater lakes and streams occur on the surface of the ice and are colonized by photosynthetic microbial mat communities. This High Arctic cryo-ecosystem is similar in several of its physical, biological and geochemical features to the McMurdo Ice Shelf in Antarctica. The ice-mats in both polar regions are dominated by filamentous cyanobacteria but also contain diatoms, chlorophytes, flagellates, ciliates, nematodes, tardigrades and rotifers. The luxuriant Ward Hunt consortia also contain high concentrations (10(7)-10(8) cm-2) of viruses and heterotrophic bacteria. During periods of extensive ice cover, such as glaciations during the Proterozoic, cryotolerant mats of the type now found in these polar ice shelf ecosystems would have provided refugia for the survival, growth and evolution of a variety of organisms, including multicellular eukaryotes.

Animals↗
PubMed1981

Nitrate accumulation in aerobic hypolimnia: relative importance of benthic and planktonic nitrifiers in an oligotrophic lake.

Both nitrate and nitrous oxide accumulate in the hypolimnion of the oligotrophic Lake Taupo, New Zealand, throughout stratification. The two forms of oxidized nitrogen increase in concentration with increasing depth toward the sediments, where the dissolved concentrations of reduced nitrogen are two orders of magnitude higher than concentrations in the overlying water. Nitrification rates were measured by dark [C]CO(2) assays with and without the inhibitor nitrapyrin. The fastest rates were recorded for planktonic nitrifiers in the epilimnion and benthic species in the surficial 2.5 mm of the sediments. Nitrifying bacteria were least active in the deep hypolimnion. Deepwater accumulation of NO(3) in Lake Taupo must therefore be a product of benthic rather than planktonic nitrification.

Journal Article↗
PubMed1979

Uptake of [14C]methylammonium by plankton communities: a comparative assay for ammonium transport systems in natural waters.

A diverse range of freshwater plankton communities were tested for their ability to take up [14C]methylammonium. Uptake occurred at low substrate levels by high-affinity, energy-requiring, transport systems which were competitively inhibited by ammonium but not by L-amino acids or nicotinamide. A simple competitive inhibition model was used to examine the effects of increasing ammonium levels on uptake in a eutrophic lake. Apparent K1 values for the labelled substrate markedly increased with increasing ammonium. The transport systems had an approximately five-fold greater affinity for ammonium than for methylammonium. The Vmax for methylammonium uptake was relatively insensitive to large changes in ambient ammonium levels. This kinetic parameter may be a useful comparative measure of ammonium transport capacity in natural waters, particularly where low ambient ammonium concentrations preclude the use of 15N.

Amino Acids↗
PubMed1970

Immunofluorescent identification of Type 12 group A streptococci.

The fluorescent antibody (FA) conjugate prepared by labeling streptococcal M type 12 antibody with fluorescein isothiocyanate was found to exhibit considerable nonspecific FA staining with other group A M-serotypes. The cross-reactions could be reduced sufficiently or eliminated by the addition of adsorbed homologous blocking serum (AHB) but not by preimmune serum. The AHB was prepared by adsorbing type 12 antiserum with untreated homologous cells. Comparative staining with unblocked and AHB-blocked FA conjugates enabled type 12 streptococci from clinical specimens to be rapidly and accurately identified.

Adsorption↗
PubMed1967

Thiobarbiturate-reacting materials in microorganisms.

The amount of thiobarbiturate-reacting material in 51 strains of bacteria and three yeasts was determined. Reactive material was found to be present in all of the gram-negative bacteria examined. It was assumed that the reactive material in this case was primarily 2-keto-3-deoxyoctonate (KDO), an eight-carbon sugar acid which is usually associated with the cell wall lipolysaccharide of members of the Salmonella-Escherichia group. Very little reactive material could be detected in the gram-positive species and yeasts that were examined. When expressed as per cent dry weight, the gram-negative bacteria exhibited about eight times more reactive material than the gram-positive species. It is suggested that the small amount of reactive material detected in gram-positive cells and yeasts is due to compounds other than KDO.

Bacteria↗