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Biomedical subjects

K A Hughes

Publications and source records attributed to K A Hughes.

At least 19 recordsLinked to original sources
PubMed2005

Low temperature bioremediation of oil-contaminated soil using biostimulation and bioaugmentation with a Pseudomonas sp. from maritime Antarctica.

AIMS: To identify native Antarctic bacteria capable of oil degradation at low temperatures. METHODS AND RESULTS: Oil contaminated and pristine soils from Signy Island (South Orkney Islands, Antarctica) were examined for bacteria capable of oil degradation at low temperatures. Of the 300 isolates cultured, Pseudomonas strain ST41 grew on the widest range of hydrocarbons at 4 degrees C. ST41 was used in microcosm studies of low temperature bioremediation of oil-contaminated soils. Microcosm experiments showed that at 4 degrees C the levels of oil degradation increased, relative to the controls, with (i) the addition of ST41 to the existing soil microbial population (bioaugmentation), (ii) the addition of nutrients (biostimulation) and to the greatest extent with (iii) a combination of both treatments (bioaugmentation and biostimulation). Addition of water to oil contaminated soil (hydration) also enhanced oil degradation, although less than the other treatments. Analysis of the dominant species in the microcosms after 12 weeks, using temporal temperature gradient gel electrophoresis, showed Pseudomonas species to be the dominant soil bacteria in both bioaugmented and biostimulated microcosms. CONCLUSIONS: Addition of water and nutrients may enhance oil degradation through the biostimulation of indigenous oil-degrading microbial populations within the soil. However, bioaugmentation with Antarctic bacteria capable of efficient low temperature hydrocarbon degradation may enhance the rate of bioremediation if applied soon after the spill. SIGNIFICANCE AND IMPACT OF THE STUDY: In the future, native soil bacteria could be of use in bioremediation technologies in Antarctica.

Alkanes↗
PubMed2005

Genetic and environmental effects on secondary sex traits in guppies (Poecilia reticulata).

Male guppies (Poecilia reticulata) exhibit extreme phenotypic and genetic variability for several traits that are important to male fitness, and several lines of evidence suggest that resource level affects phenotypic expression of these traits in nature. We tested the hypothesis that genetic variation for male secondary sex traits could be maintained by genotype-specific effects of variable resource levels (genotype-environment interaction). To do this, we measured genetic variation and covariation under two environmental conditions--relatively low and relatively high food availability. We found high levels of genetic variation for most traits, but we only found a significant G x E interaction across food levels for one trait (body size) for one population. The across-environment correlations for size were large and positive, indicating that the reaction norms for size did not cross. We also found that male colour pattern elements had nearly an order of magnitude more genetic variation than did male size. Heritability estimates indicated that Y-linked genes are responsible for some of the genetic variation in male size and colour traits. We discuss implications of these results for theories of the maintenance of genetic variation in male secondary sexual traits in guppies.

Animals↗
PubMed2004

A preliminary study of airborne microbial biodiversity over Peninsular Antarctica.

This study used PCR-based molecular biological identification techniques to examine the biodiversity of air sampled over Rothera Point (Antarctic Peninsula). 16S rDNA fragments of 132 clones were sequenced and identified to reveal a range of microorganisms, including cyanobacteria, actinomycetes, diatom plastids and other uncultivated bacterial groups. Matches for microorganisms that would be considered evidence of human contamination were not found. The closest matches for many of the sequences were from Antarctic clones already in the databases or from other cold environments. Whilst the majority of the sequences are likely to be of local origin, back trajectory calculations showed that the sampled air may have travelled over the Antarctic Peninsula immediately prior to reaching the sample site. As a result, a proportion of the detected biota may be of non-local origin. Conventional identification methods based on propagule morphology or culture are often inadequate due to poor preservation of characteristic features or loss of viability during airbome transfer. The application of molecular biological techniques in describing airbome microbial biodiversity represents a major step forward in the study of airborne biota over Antarctica and in the distribution of microorganisms and propagules in the natural environment.

Air Microbiology↗
PubMed2001

Male genotype affects female longevity in Drosophila melanogaster.

Several recent studies suggest that interactions with conspecific males can reduce the longevity of female Drosophila melanogaster or support the idea that male and female fitness components are involved in antagonistic interactions. Here we report that males from third-chromosome isogenic lines demonstrated significant genetic variation in male reproductive performance and in the longevity of their mates. Increased male performance was marginally significantly associated with one measure of increased female survival rate. However, there was no indication of tradeoffs or negative correlations between male reproductive success and female survival. We discuss alternative hypotheses for the cause of the induced variation in female longevity.

Animals↗
PubMed2000

Small molecule-based chemical affinity system for the purification of proteins.

A new chemical affinity system is described for the purification of proteins. The Linx Affinity Purification System enables researchers to quickly and easily bind a protein ligand to a chromatographic matrix and use the resulting affinity resin to purify a second protein from crude mixtures. The entire process takes approximately 2 h.

Animals↗
PubMed1999

Toward reconciling inferences concerning genetic variation in senescence in Drosophila melanogaster.

Standard models for senescence predict an increase in the additive genetic variance for log mortality rate late in the life cycle. Variance component analysis of age-specific mortality rates of related cohorts is problematic. The actual mortality rates are not observable and can be estimated only crudely at early ages when few individuals are dying and at late ages when most are dead. Therefore, standard quantitative genetic analysis techniques cannot be applied with confidence. We present a novel and rigorous analysis that treats the mortality rates as missing data following two different parametric senescence models. Two recent studies of Drosophila melanogaster, the original analyses of which reached different conclusions, are reanalyzed here. The two-parameter Gompertz model assumes that mortality rates increase exponentially with age. A related but more complex three-parameter logistic model allows for subsequent leveling off in mortality rates at late ages. We find that while additive variance for mortality rates increases for late ages under the Gompertz model, it declines under the logistic model. The results from the two studies are similar, with differences attributable to differences between the experiments.

Aging↗
PubMed1998

Bacteriophage and associated polysaccharide depolymerases--novel tools for study of bacterial biofilms.

Bacteriophage for three representative strains of Gram-negative biofilm bacteria have proved to be of widespread occurrence. Lytic bacteriophage have been isolated from local sewage for the bacterium 1.15, an exopolysaccharide (EPS)-producing pseudomonad found originally as a component of biofilms in a local river, and for two Enterobacter agglomerans strains from industrial biofilms. Representative examples of all three bacteriophage possess a relatively low burst size and on solid media, exhibit very large plaques surrounded by a wide halo (5-20 mm) indicative of polysaccharide depolymerase action. The bacteriophage are thus similar to other viruses for EPS-producing bacteria in inducing the synthesis of enzymes degrading the polymers which occlude the bacterial cell surface. In each preparation, the polysaccharase activity was associated both with sedimented phage particles and with the supernate of bacterial lysates. The enzymes have been partially purified and used to prepare polysaccharide digests in which the major products from each polysaccharide are the presumed repeat units of the polymers or oligomers of these. The soluble phage enzymes each degrade their substrate by acting as endo-glycanohydrolases. The phage and their associated enzymes thus provide very useful highly specific tools for studies of biofilms incorporating the bacterial host strains. Their potential applications in studies on bacterial biofilms are discussed.

Bacteriophages↗
PubMed1997

The effects of spontaneous mutation on quantitative traits. II. Dominance of mutations with effects on life-history traits.

We studied the dominance of the effects of chromosomes carrying unselected mutations on five life-history traits in Drosophila melanogaster. Mutations were accumulated on the second chromosome for 44 generations in the absence of natural selection. Traits studied were female fecundity early and late in adult life, male mating ability, and male and female longevity. Homozygous effects were estimated for 50 mutant lines, and heterozygous effects were estimated by crossing these lines in a partial diallel scheme. Direct estimates of dominance showed that the effects of mutants are at least partially recessive. Heterozygotes had higher trait means than homozygotes in all five cases, and these differences were significant for late fecundity and female longevity. For all traits, genetic variance was larger among homozygous crosses than among heterozygous crosses. These results are consistent with those of many other studies that suggest that both unselected mutations and those found segregating in natural populations are partially recessive.

Animals↗
PubMed1997

Quantitative genetics of sperm precedence in Drosophila melanogaster.

To assess the genetic basis of sperm competition under conditions in which it occurs, I estimated additive, dominance, homozygous and environmental variance components, the effects of inbreeding, and the weighted average dominance of segregating alleles for two measures of sperm precedence in a large, outbred laboratory population. Both first and second male precedence show significant decline on inbreeding. Second male precedence demonstrates significant dominance variance and homozygous genetic variance, but the additive variance is low and not significantly different from zero. For first male precedence, the variance among homozygous lines is again significant, and dominance variance is larger than the additive variance, but is not statistically significant. In contrast, male mating success and other fitness components in Drosophila generally exhibit significant additive variance and little or no dominance variance. Other recent experiments have shown significant genotypic variation for sperm precedence and have associated it with allelic variants of accessory-gland proteins. The contrast between sperm precedence and other male fitness traits in the structure of quantitative genetic variation suggests that different mechanisms may be responsible for the maintenance of variation in these traits. The pattern of genetic variation and inbreeding decline shown in this experiment suggests that one or a few genes with major effects on sperm precedence may be segregating in this population.

Animals↗
PubMed1996

Radiolytic protein surface mapping.

We report that high energy beta particles may function as a means for mapping the surface of a protein. Comparable to Fe-EDTA in the presence of ascorbate and peroxide, 90Y-EDTA alone can break polypeptide backbone bonds on the surface of E. coli RNA polymerase. The two methods give very similar fragmentation patterns, although some unique fragments are produced by each. Radiolytic footprinting may prove useful for mapping proteins inside living cells, since beta-radiolysis produces reactive species up to approximately 1 cm away from the emitting 90Y.

Beta Particles↗
PubMed1996

Age-specific inbreeding depression and components of genetic variance in relation to the evolution of senescence.

Two major theories of the evolution of senescence (mutation accumulation and antagonistic pleiotropy) make different predictions about the relationships between age, inbreeding effects, and the magnitude of genetic variance components of life-history components. We show that, under mutation accumulation, inbreeding decline and three major components of genetic variance are expected to increase with age in randomly mating populations. Under the simplest version of the antagonistic pleiotropy model, no changes in the severity of inbreeding decline, dominance variance, or the genetic variance of chromosomal homozygotes are expected, but additive genetic variance may increase with age. Age-specific survival rates and mating success were measured on virgin males, using lines extracted from a population of Drosophila melanogaster. For both traits, inbreeding decline and several components of genetic variance increase with age. The results are consistent with the mutation accumulation model, but can only be explained by antagonistic pleiotropy if there is a general tendency for an increase with age in the size of allelic effects on these life-history traits.

Aging↗
PubMed1996

Binding of the sigma 70 protein to the core subunits of Escherichia coli RNA polymerase, studied by iron-EDTA protein footprinting.

We have used a nonspecific protein cleaving reagent to map the interactions between subunits of the multisubunit enzyme RNA polymerase (Escherichia coli). We developed suitable conditions for using an untethered Fe-EDTA reagent, which does not bind significantly to proteins. Comparison of the cleaved fragments of the subunits from the core enzyme (alpha 2 beta beta') and the holoenzyme (core+sigma 70) shows that absence of the sigma 70 subunit is associated with the appearance of several cleavage sites on the subunits beta (within 10 residues of sequence positions 745, 764, 795, and 812) and beta' (within 10 residues of sequence positions 581, 613, and 728). A cleavage site near beta residue 604 is present in the holoenzyme but absent in the core, demonstrating that a conformational change occurs when sigma 70 binds. No differences are observed for the alpha subunit.

Amino Acid Sequence↗
PubMed1995

The inbreeding decline and average dominance of genes affecting male life-history characters in Drosophila melanogaster.

This paper describes the results of assays of male life-history characters in a large outbred laboratory population of D. melanogaster. Lines of flies homozygous for the entire third chromosome and lines of flies carrying two different third chromosomes were assayed for age-specific male mating ability (MMA), age-specific survivorship, male fertility, and body mass. The results of these assays were used to calculate the inbreeding decline associated with each of these traits, the average dominance of deleterious alleles that affect the traits, the genotypic and environmental components of variance for the homozygous lines, and phenotypic and genotypic correlations among the characters. Significant inbreeding decline was found for all characters except the Gompertz intercept and fertility. Early and late MMA show larger effects of inbreeding than any other trait. The inbreeding load for MMA is about the same magnitude as that for egg-to-adult viability, but is substantially less than that associated with total fitness. The estimated inbreeding decline and average dominance of male life-history characters are comparable to estimates for other Drosophila fitness components.

Alleles↗
PubMed1994

An experimental study of inbreeding depression in a natural habitat.

Inbreeding is known to lead to decreased survival and reproduction in captive populations of animals. It is also important to know whether inbreeding has deleterious effects in natural habitats. An estimate was made of the effects of inbreeding in white-footed mice, Peromyscus leucopus noveboracensis, derived from a wild population. This study demonstrates that inbreeding had a significant detrimental effect on the survivorship of mice reintroduced into a natural habitat. This effect was more severe than the effect observed in laboratory studies of the population.

Analysis of Variance↗
PubMed1994

A genetic analysis of senescence in Drosophila.

Two attractive theories for the evolution of senescence are based on the principle that the force of natural selection decreases with age. The theories differ in the type of age-specific gene action that they assume. Antagonistic pleiotropy postulates that pleiotropic genes with positive effects early in life and negative effects of comparable magnitude late in life are favoured by selection, whereas genes with the reverse pattern of action are selected against. Mutation accumulation assumes that deleterious mutant alleles with age-specific effects will equilibrate at a lower frequency if their effects are expressed early rather than late in life. Explicit models demonstrate that both mechanisms can lead to the evolution of senescent life histories under reasonable conditions. Antagonistic pleiotropy has gained considerable empirical support, but the evidence in support of mutation accumulation is more sparse. Here we report that the genetic variability of mortality in male Drosophila melanogaster increases greatly at very late ages, as predicted by the mutation accumulation hypothesis. The rate of increase in mortality with age exhibits substantial genetic and environmental variability. This result provides a possible explanation for recent observations of non-increasing mortality rates in very old flies.

Aging↗
PubMed1994

Visual assessment of hemiplegic gait following stroke: pilot study.

A form that will guide clinicians through a reliable and valid visual assessment of hemiplegic gait was designed. Six hemiplegic patients were filmed walking along an instrumented walkway. These films were shown to three physiotherapists who used the form to rate the patients' gait. Each physiotherapist rated the six patients at both stages of recovery, repeating this a further two times. This resulted in 108 completed forms. Within-rater reliability is statistically significant for some raters and some individual form sections. Between-rater reliability is significant for some sections. Detailed analysis has shown that parts of the form have caused reduced reliability. These are mainly sections that ask for severity judgments or are duplicated. Some indication of normal gait should be included on the form. To test validity fully the form should be tested on a group of patients who all have significant changes in each objective gait measurement.

Cerebrovascular Disorders↗
PubMed1994

Effects of autosomal inversions on meiotic exchange in distal and proximal regions of the X chromosome in a natural population of Drosophila melanogaster.

We have investigated the interchromosomal effect of the naturally-occurring paracentric inversions In(2L)t and In(3R)P on meiotic recombination in two regions of the X chromosome in Drosophila melanogaster. Previous authors have suggested that the rate of recombination at the tip of the X chromosome may be substantially higher in some natural populations than values measured in the laboratory, due to the interchromosomal effect of heterozygous autosomal inversions. This suggestion was motivated by observations that transposable elements are not as common at the tip of the X chromosome as predicted by recent research relating reduced meiotic exchange to increased element abundance in D. melanogaster. We examined the effects of heterozygous In(2L)t and In(3R)P on recombination at both the tip and base of the X chromosome on a background of isogenic major chromosomes from a natural population. Both inversions substantially increased the rate of recombination at the base; neither one affected recombination at the tip. The results suggest that the presence of inversions in the study population does not elevate rates of crossing over at the tip of the X chromosome. The relevance of these results to ideas relating transposable element abundance to recombination rates is discussed.

Animals↗