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PubMed2006

Identification of a polymeric Ig receptor binding phage-displayed peptide that exploits epithelial transcytosis without dimeric IgA competition.

The polymeric Ig receptor (pIgR), also called membrane secretory component (SC), mediates epithelial transcytosis of polymeric immunoglobulins (pIgs). J Chain-containing polymeric IgA (pIgA) and pentameric IgM bind pIgR at the basolateral epithelial surface. After transcytosis, the extracellular portion of the pIgR is cleaved at the apical side, either complexed with pIgs as bound SC or unoccupied as free SC. This transport pathway may be exploited to target bioactive molecules to the mucosal surface. To identify small peptide motifs with specific affinity to human pIgR, we used purified free SC and selection from randomized, cysteine-flanked 6- and 9-mer phage-display libraries. One of the selected phages, called C9A, displaying the peptide CVVWMGFQQVC, showed binding both to human free SC and SC complexed with pIgs. However, the pneumococcal surface protein SpsA (Streptococcus pneumoniae secretory IgA-binding protein), which binds human SC at a site distinct from the pIg binding site, competed with the C9A phage for binding to SC. The C9A phage showed greatly increased transport through polarized Madin-Darby canine kidney cells transfected with human pIgR. This transport was not affected by pIgA nor did it inhibit pIgR-mediated pIgA transcytosis. A free peptide of identical amino acid sequence as that displayed by the C9A phage inhibited phage interaction with SC. This implied that the C9A peptide sequence may be exploited for pIgR-mediated epithelial transport without interfering with secretory immunity.

Animals↗
PubMed1985

The population dynamics of competition between parasites.

A number of published studies of competition between parasite species are examined and compared. It is suggested that two general levels of interaction are discernible: these correspond to the two levels of competition recognized by workers studying free-living animals and plants: 'exploitation' and 'interference' competition. The former may be defined as the joint utilization of a host species by two or more parasite species, while the latter occurs when antagonistic mechanisms are utilized by one species either to reduce the survival or fecundity of a second species or to displace it from a preferred site of attachment. Data illustrating both levels of interaction are collated from a survey of the published literature and these suggest that interference competition invariably operates asymmetrically. The data are also used to estimate a number of population parameters which are important in determining the impact of competition at the population level. Theoretical models of host-parasite associations for both classes of competition are used to examine the expected patterns of population dynamics that will be exhibited by simple two-species communities of parasites that utilize the same host population. The analysis suggests that the most important factor allowing competing species of parasites to coexist is the statistical distribution of the parasites within the host population. A joint stable equilibrium should be possible if both species are aggregated in their distribution. The size of the parasite burdens at equilibrium is then determined by other life-history parameters such as pathogenicity, rates of resource utilization and antagonistic ability. Comparison of these theoretical expectations with a variety of sets of empirical data forms the basis for a discussion about the importance of competition in natural parasite populations. The models are used to assess quantitatively the potential for using competing parasite species as biological control agents for pathogens of economic or medical importance. The most important criterion for identifying a successful control agent is an ability to infect a high proportion of the host population. If such a parasite species also exhibits an intermediate level of pathology or an efficient ability to utilize shared common resources, antagonistic interactions between the parasite species contribute only secondarily to the success of the control. Competition in parasites is compared with competition in free-living animals and plants. The comparison suggests further experimental tests which may help to assess the importance of competition in determining the structure of more complex parasite-host communities.

Animals↗
PubMed2002

Competitive displacement among insects and arachnids.

Competitive displacement is the most severe outcome of interspecific competition. For the purposes of this review, we define this type of displacement as the removal of a formerly established species from a habitat as a result of direct or indirect competitive interactions with another species. We reviewed the literature for recent putative cases of competitive displacement among insects and arachnids and assessed the evidence for the role of interspecific competition in these displacements. We found evidence for mechanisms of both exploitation and interference competition operating in these cases of competitive displacement. Many of the cases that we identified involve the operation of more than one competitive mechanism, and many cases were mediated by other noncompetitive factors. Most, but not all, of these displacements occurred between closely related species. In the majority of cases, exotic species displaced native species or previously established exotic species, often in anthropogenically-altered habitats. The cases that we identified have occurred across a broad range of taxa and environments. Therefore we suggest that competitive displacement has the potential to be a widespread phenomenon, and the frequency of these displacement events may increase, given the ever-increasing degree of anthropogenic changes to the environment. A greater awareness of competitive displacement events should lead to more studies documenting the relative importance of key factors and developing hypotheses that explain observed patterns.

Animals↗
PubMed2000

The Population Dynamics and Community Ecology of Root Hemiparasitic Plants.

Root hemiparasitic plants and their host plants interact directly, through parasitism, as well as indirectly, through scramble competition for resources. To understand the population dynamics and community ecology of root hemiparasitic plants and their hosts, models of resource-based competition have been extended to include resource parasitism. Parasitism provides a mechanism for parasitic plants to overcome deficits in their ability to compete for soil resources. The interaction ranges from competitive to exploiter-victim, depending on whether the benefits of parasitism overshadow the costs of competition. These models predict that as productivity in the system increases, parasitic plants should become more abundant. In diverse host communities, differences in the impact that parasites have on their hosts and the benefits that they receive from parasitizing different hosts may lead to nontransitive competitive relationships and a sort of apparent competition. The possible dynamics include paper-rock-scissors oscillations and indirect mutualisms between parasitic plants and their hosts that allow them to form coalitions that can exclude competitive dominants.

degree of parasitism↗
PubMed2003

Homogeneous assay for biotin based on Aequorea victoria bioluminescence resonance energy transfer system.

Here we describe a homogeneous assay for biotin based on bioluminescence resonance energy transfer (BRET) between aequorin and enhanced green fluorescent protein (EGFP). The fusions of aequorin with streptavidin (SAV) and EGFP with biotin carboxyl carrier protein (BCCP) were purified after expression of the corresponding genes in Escherichia coli cells. Association of SAV-aequorin and BCCP-EGFP fusions was followed by BRET between aequorin (donor) and EGFP (acceptor), resulting in significantly increasing 510 nm and decreasing 470 nm bioluminescence intensity. It was shown that free biotin inhibited BRET due to its competition with BCCP-EGFP for binding to SAV-aequorin. These properties were exploited to demonstrate competitive homogeneous BRET assay for biotin.

Aequorin↗
PubMed1998

High population density in bank voles stimulates food hoarding after breeding.

The effects of conspecific density (i.e. risk of intraspecific competition) on hoarding behaviour were studied in breeding pairs of bank voles, Clethrionomys glareolus. I simulated high population density by using odours of conspecifics, to exclude the direct effects of exploitation or interference competition for food. The pairs of bank voles hoarded only at the end of their breeding season. Hoarding was not correlated with whether the voles had a litter during the experiment or their litter size, but was more likely at the high population density and for pairs with small females. This may indicate that smaller females especially make caches in the autumn, possibly to ensure better winter survival under high population density. I discuss the hoarding behaviour of bank voles in relation to their territorial behaviour and food resources during the breeding season and predictable population changes during winter. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Prospects for 'competitive exclusion' treatment to control salmonellas and other foodborne pathogens in poultry.

In newly hatched chicks, the rapid establishment of an adult-type intestinal microflora, via the oral route, produces almost immediate resistance to colonization by any food poisoning salmonellas that gain access to the rearing environment. Exploitation of the 'competitive exclusion' (CE) effect is now an accepted part of the overall strategy by which poultry-associated salmonellas are being controlled in some countries. This review covers practical aspects of CE treatment and factors affecting efficacy in both laboratory-scale trials and field studies. It also considers possible applications in preventing colonization of poultry with Escherichia coli O157 and Campylobacter jejuni. For the latter, evidence suggests that the 'protective' organisms are different from those involved in salmonella control.

Animal Husbandry↗
PubMed1992

Alternative starting materials for industrial processes.

In the manufacture of chemical feedstocks and subsequent processing into derivatives and materials, the U.S. chemical industry sets the current standard of excellence for technological competitiveness. This world-class leadership is attributed to the innovation and advancement of chemical engineering process technology. Whether this status is sustained over the next decade depends strongly on meeting increasingly demanding challenges stimulated by growing concerns about the safe production and use of chemicals without harmful impacts on the environment. To comply with stringent environmental regulations while remaining economically competitive, industry must exploit alternative benign starting materials and develop environmentally neutral industrial processes. Opportunities are described for development of environmentally compatible alternatives and substitutes for some of the most abundantly produced, potentially hazardous industrial chemicals now labeled as "high-priority toxic chemicals." For several other uniquely important commodity chemicals where no economically competitive, environmentally satisfactory, nontoxic alternative starting material exists, we advocate the development of new dynamic processes for the on-demand generation of toxic chemicals. In this general concept, which obviates mass storage and transportation of chemicals, toxic raw materials are produced in real time, where possible, from less-hazardous starting materials and then chemically transformed immediately into the final product. As a selected example for semiconductor technology, recent progress is reviewed for the on-demand production of arsine in turnkey electrochemical generators. Innovation of on-demand chemical generators and alternative processes provide rich areas for environmentally responsive chemical engineering processing research and development for next-generation technology.

Journal Article↗
PubMed1999

Growth and survivorship of dipterocarp seedlings: differences in shade persistence create a special case of dispersal limitation.

A series of growth experiments and observations on natural populations have been carried out on dipterocarp species of contrasting ecology growing in artificial gaps and the forest understorey. These studies have demonstrated that although differences exist between species in photosynthetic and growth responses to the high-light environment, competition for light in canopy gaps is highly asymmetrical and tends to reinforce any pre-existing dominance hierarchy. We propose that differences in seedling persistence in forest canopy shade are highly influenced by species-specific biotic and abiotic interactions. Our experiments suggest that as seedlings, dipterocarp species trade off traits which enhance persistence and growth in shade against those that enhance their ability to exploit gaps. Less competitive species survive for progressively longer periods of time after a gregarious fruiting event. This leads to significant shifts with time in the number of species present in the seedling bank and hence in the importance of interspecific competition in determining which species dominates regrowth in gaps. We propose that this special case of dispersal limitation is more likely to account for coexistence of dipterocarp species than differences in growth responses to gaps of different size, with stochastic and environmental variables interacting to determine species distribution and abundance.

Ecosystem↗
PubMed2006

Coexistence in the chemostat as a result of metabolic by-products.

Classical chemostat models assume that competition is purely exploitative and mediated via a common, limiting and single resource. However, in laboratory experiments with pathogens related to the genetic disease Cystic Fibrosis, species specific properties of production, inhibition and consumption of a metabolic by-product, acetate, were found. These assumptions were implemented into a mathematical chemostat model which consists of four nonlinear ordinary differential equations describing two species competing for one limiting nutrient in an open system. We derive classical chemostat results and find that our basic model supports the competitive exclusion principle, the bistability of the system as well as stable coexistence. The analytical results are illustrated by numerical simulations performed with experimentally measured parameter values. As a variant of our basic model, mimicking testing of antibiotics for therapeutic treatments in mixed cultures instead of pure ones, we consider the introduction of a lethal inhibitor, which cannot be eliminated by one of the species and is selective for the stronger competitor. We discuss our theoretical results in relation to our experimental model system and find that simulations coincide with the qualitative behavior of the experimental result in the case where the metabolic by-product serves as a second carbon source for one of the species, but not the producer.

Acetic Acid↗
PubMed1993

Exploiting mechanistic differences between drug classes to define functional drug interaction domains on topoisomerase II. Evidence that several diverse DNA cleavage-enhancing agents share a common site of action on the enzyme.

To fully understand the mechanism of action of topoisomerase II-targeted agents, the effects of these drugs on the catalytic cycle of the enzyme must be well characterized. The present study utilized a nonturnover DNA catenation assay to determine the effects of several drugs (etoposide, genistein, CP-115,953, amsacrine, and novobiocin) on the DNA strand passage event mediated by topoisomerase II. With the exception of etoposide, all of the drugs inhibited the DNA strand passage step of the topoisomerase II catalytic cycle. A series of drug competition experiments that exploited this mechanistic difference was used to determine relationships between drug interaction domains on the enzyme. While the inclusion of etoposide in nonturnover DNA catenation assays reversed the inhibition of strand passage induced by genistein, CP-115,953, and amsacrine, it had no effect on the inhibition induced by novobiocin. These results strongly suggest that etoposide can displace other DNA cleavage-enhancing agents from the enzyme.DNA complex. Therefore, it is concluded that the interaction domain of etoposide overlaps those of several DNA cleavage-enhancing drugs but, consistent with previous observations (Robinson, M. J., Corbett, A. H., and Osheroff, N. (1993) Biochemistry 32, 3638-3643), is distinct from that of novobiocin.

Amsacrine↗
PubMed2006

Space invaders? A search for patterns underlying the coexistence of alien black rats and Galápagos rice rats.

The introduction and spread of the black rat Rattus rattus is believed to have caused the worst decline of any vertebrate taxon in Galápagos. However, the "extinct" Santiago rice rat Nesoryzomys swarthi has recently been rediscovered in sympatry with R. rattus providing the first exception to this general pattern of displacement. We carried out an exploratory investigation of this novel system with the aim of identifying patterns that may facilitate the apparent coexistence of the two species. We carried out an extensive survey of Santiago Island to map the current distribution of the endemic rice rat and to explore broad scale distribution-habitat associations. We then used live-trapping, radio-tracking, and spool-and-line tracking to quantify abundance-habitat correlations and to test for evidence of interspecific spatial segregation, alteration of N. swarthi activity patterns (spatial and temporal), and microhabitat partitioning. We found that N. swarthi has disappeared from part of its historical range and appears to be restricted to a 14 km stretch of the north-central coast, characterised by high density of the cactus Opuntia galapageia. In contrast, the generalist R. rattus was found at all survey sites. We found no evidence of spatial segregation, and home range size, temporal activity and density of N. swarthi did not vary with local density of R. rattus. However, pre-dawn and post-dusk N. swarthi activity levels increased with R. rattus density perhaps reflecting an increase in foraging effort necessary to compensate for the costs of interspecific exploitation or interference competition. The distribution, microhabitat selection, and abundance-habitat relations of N. swarthi suggest that the endemic cactus O. galapageia may facilitate interspecific coexistence. Further research should include a comparison of inter-seasonal resource preference and foraging activity of the two species coupled with replicated field experiments to confirm and quantify competition and to elucidate the mechanism of competitive coexistence.

Animals↗
PubMed2006

Globalization and fruitfly invasion and expansion: the medfly paradigm.

The phytophagous insects of the Tephritidae family commonly referred to as "true fruit flies" offer different case histories of successful invasions. Mankind has played an important role in altering the distributions of some of the more polyphagous and oligophagous species. However, the question arises why only a few species have become major invaders. The understanding of traits underlying adaptation in different environments is a major topic in invasion biology. Being generalists or specialists, along the K-r gradient of the growth curve, make a difference in term of food resources exploitation and interspecies competition and displacement. The species of the genus Ceratitis are good examples of r-strategists. The genetic and biological data of the most notorious Ceratitis species, the Mediterranean fruit fly Ceratitis capitata (medfly), are reviewed to investigate the traits and behaviours that make the medfly an important invader. It can be learnt from medfly, that invasions in a modern global trade network tend to be due to multiple introductions. This fact allows a maintenance or enhancement of genetic variability in the adventive populations, which in turn increases their potential invasiveness. Our current knowledge of the medfly genome opens the way for future studies on functional genomics.

Animals↗
PubMed1992

Contingent and non-contingent biofeedback training for Type A and B healthy adults: can Type As relax by competing?

This paper investigates an alternative approach to the modification of cardiovascular reactivity in healthy Type A adults using contingent (true) and non-contingent (false) heart rate biofeedback. Sixteen Type A and sixteen Type B subjects were either given instructions to compete for heart rate reduction or were given no competitive instructions. There were four relaxation sessions. In one, subjects were given contingent heart rate biofeedback and in another they were given no feedback. In two sessions 'feedback' was non-contingent: in one condition feedback suggested that heart rate decreased across the session; in the other the suggestion was of increase. Results showed that overall, biofeedback was an effective method for heart rate reduction but non-contingent feedback (decreased heart rate) was found to be as effective as contingent feedback. Overall, Type A subjects reduced heart rate significantly more than Type Bs. More importantly, Type As reduced heart rate significantly more when competing than when competition was not mentioned. These results suggest that core elements of Type A behaviour, in particular competition, could be exploited in the modification of physiological hyperactivity in healthy Type A individuals.

Adaptation, Psychological↗
PubMed2002

The ecology of fish parasites with particular reference to helminth parasites and their salmonid fish hosts in Welsh rivers: a review of some of the central questions.

Ecological studies carried out in Welsh rivers on the feeding behaviour of salmonid fish, their helminth parasites and intermediate hosts in the early 1950s and in 1998 have been used as a basis to review the literature dealing with the following questions. First, how are the helminth populations dispersed in space-time? Second, to what extent are the distributional patterns and the life history strategies of the parasites influenced by physicochemical factors? Third, to what extent are populations of helmith parasites in salmonid fish influenced by host characteristics including the genome, sex, age, size, social position and Feeding behaviour? Fourth, are the populations of parasites regulated in a density-dependent manner? Fifth, do the parasites influence the survival and wellbeing of their salmonid hosts and the evolution of sex? Sixth, to what extent is the parasite community influenced by environmental changes including those of an anthropogenic nature and can the parasites be used as bioindicators of pollution? As with most parasites the helminth species found were highly overdispersed thus making it necessary to undertake a log10 (1 + x) conversion for statistical analyses. Statistical analyses confirm that the genome, age and sex of salmonid fish hosts, the station and seasonal change in radiation levels were significant factors in predicting the number of parasites. The evidence given supports the hypothesis that the feeding behaviour and habitat selection by the host fish, their position in the social hierarchy and the overdispersed nature of the transmission sites are the key factors in causing differences in the parasitic fauna related to host species, age, size and sex. Differences in the helminth parasite community related to station can be explained on the basis of differences in water types, sediments and chemistry. Although the evidence presented is in accord with the consensus view that temperature is correlated with seasonal changes in the abundance of many species of helminth parasites, it is argued that it may not be the direct causative mechanism. It is postulated that the life history strategy that results in a decline in abundance of the more vulnerable adult parasites in the gut of the salmonid hosts during the summer has arisen as a result of evolutionary pressures. At this time, the gut environment is particularly inhospitable because of the temperature-related enhancement of the host's immune mechanism and the increased gut turnover rate. In contrast, the larval stages in the immunologically and metabolically more benign intermediate host would be under less intensive selective pressures. It is postulated therefore that evolutionary pressures have caused the parasites to leave the definitive host and concentrate their reproductive efforts in the intermediate hosts during the warmer months. Evidence is given in support of the hypothesis that the parasite populations are regulated in a density-dependent manner and that the regulatory mechanisms may involve the host's immune mechanisms and intraspecies competition and interspecies competition of an exploitative or interference nature. Quantitative studies using 'K' factor analysis and biochemical research to elucidate the nature of the interference mechanisms are required to test this hypothesis. The absence of age-related resistance indicates an old and stable relationship in which the immunosuppressive and immunoavoidance mechanisms of the parasites and hosts, respectively, are in balance. This indicates that the introduction of novel parasites or new genetic strains of host fish could result in harmful epidemics. Despite causing tissue damage, there was no evidence of parasite-induced mortality among the salmonids in the Teifi. This finding is in accord with the generally accepted view that most freshwaters are not troubled by parasite problems. although parasites are present in abundance. In fact, parasite abundance in the salmonid fish in the Teifi was positively correlated with the condition factor and the adipose index. Two testable hypotheses were advanced to explain these observations. First, the more dominant well-conditioned fish in the hierarchy are more likely to acquire parasites because they ingest more food items and spend more time in sheltered habitats with depositing sediments where transmission mainly occurs. Second, the parasites may release factors that stimulate the host's immune and endocrinological systems to produce factors that enhance somatic growth and inhibit reproduction of the host. This benign relationship is considered to be indicative of long-term coevolution. The sex of the fish had a significant influence on the abundance of the parasites in total and also on particular species with the bias in all cases being in favour of the female fish. This review shows that sex bias in parasitism is generally not strong and that male bias in parasitism is not a general rule. Taken as a whole, the results fail to support most of the predictions based on the Hamilton-Zuk and the immunocompetence hypotheses. Possible hypotheses to explain why parasitism tends to be higher in female than in male trout include testosterone immunosuppression, corticosteroid-based immune suppression and differences between the size and behaviour of the sexes. However, the latter two hypotheses have more credence, although testosterone levels are higher in female than male trout. Between the early 1950s and 1998 there has been a marked decline in the prevalence, abundance and diversity of the helminth parasite communities in salmonid fish as well as their intermediate hosts. Possible reasons for these declines include heavy metal pollution, increased acidity and habitat degradation linked to changes in land use. It is concluded that although helminth parasites can provide supplementary information on pollution. the use of biotic indices based on the Biological monitoring working party (BMWP) or River invertebrate prediction and classification system (RIVPACS) methods are preferable. However, as these methods were designed to measure the impact of organic pollution they lack the sensitivity for measuring metal pollution. It is advocated therefore that new biomonitoring methods should be developed to measure the impact of heavy metal pollution using biotic indices based on the sampling of the susceptible invertebrate communities inhabiting depositing sediments in the transmission sites of helminth parasites.

Animals↗
PubMed2000

Human cytomegalovirus detection by a quartz crystal microbalance immunosensor.

A piezoelectric affinity sensor has been developed to detect distinctive antigens of the human cytomegalovirus. Either the specific antibodies or the antigen were immobilized on the gold electrode. To develop a rapid immunoassay, various assay formats were tested in relation with the different antigen composition. First, a direct assay was carried out immobilizing the specific antibody on the crystal surface by passive adsorption. Next, Protein A, thiol/poly L-lysine mixed self-assembled monolayers were tested as methods of gold modification. A competitive format was exploited by immobilization of the antigen onto the crystal activated by SAM and poly L-lysine. This procedure yielded a preliminary calibration curve. A linear range between 2.5 and 5 µg/ml of gB epitope in solution and a detection limit of 1 µg/ml were measured.

Journal Article↗
PubMed2003

Optimization, conflict, and nonoverlapping foraging ranges in ants.

An organism's foraging range depends on the behavior of neighbors, the dynamics of resources, and the availability of information. We use a well-studied population of the red harvester ant Pogonomyrmex barbatus to develop and independently parameterize models that include these three factors. The models solve for an allocation of foraging ants in the area around the nest in response to other colonies. We compare formulations that optimize at the colony or individual level and those that do or do not include costs of conflict. Model predictions were compared with data collected on ant time budgets and ant density. The strategy that optimizes at the colony level but neglects costs of conflict predicts unrealistic levels of overlap. In contrast, the strategy that optimizes at the individual level predicts realistic foraging ranges with or without inclusion of conflict costs. Both the individual model and the colony model that includes conflict costs show good quantitative agreement with data. Thus, an optimal foraging response to a combination of exploitation and interference competition can largely explain how individual foraging behavior creates the foraging range of a colony. Deviations between model predictions and data indicate that colonies might allocate a larger than optimal number of foragers to areas near boundaries between foraging ranges.

Animals↗
PubMed1989

Source of methyl groups in brain and nerve tissue in the rat.

Previous studies that demonstrated that mouse brain accumulated significantly more radioactivity from subcutaneously administered 5-methyltetrahydrofolate labelled in the methyl group compared to the label in the folate moiety are open to two interpretations. The methyl group could have been transferred to another compound (probably methionine) prior to its transport into the brain. Alternatively, if plasma 5-methyltetrahydrofolate per se is significantly involved in the provision of methyl groups to brain and nerve tissue it would be expected that the folate moiety would be returned to the plasma to complete the cycle and thus would appear not to have been taken up. In this article, using competition experiments that exploit the differences in the mechanism of transport of methionine and 5-methyltetrahydrofolate into brain and nerve, evidence is presented that in the rat the methyl group of 5-methyltetrahydrofolate is transported after its conversion to methionine.

Animals↗