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PubMed1991

Procedure for Obtaining Efficient Root Nodulation of a Pea Cultivar by a Desired Rhizobium Strain and Preempting Nodulation by Other Strains.

The specificity between the sym-2 gene bred into certain cultivars of pea (Pisum sativum L.) and the nodX gene, present only rarely in isolates of Rhizobium leguminosarum, can be exploited to preempt competition or nodulation blocking by a Rhizobium strain indigenous to a soil environment. The principle is to isolate an R. leguminosarum strain prevalent in a locale, convert it into a strain that will nodulate a desirable pea cultivar carrying sym-2 by establishing nodX in it, and then use the resulting Rhizobium strain with the pea cultivar carrying sym-2. To accomplish this, we first constructed a transposon Tn5 derivative called Tn5nodX and an efficient delivery vehicle that is suicidal in R. leguminosarum. We tested the potential utility of the system in greenhouse experiments. The results are encouraging enough to warrant extensive experiments under field conditions.

Journal Article↗

PubMed1997

[Implications of spatial aggregation of parasites for the population dynamics in host-parasite interaction].

Some aspects of the widely observed over-dispersed pattern of the distribution of parasites within the host population are examined. It has been established in the parasitological literature that most hosts usually harbour few parasites, while only few hosts harbour a large proportion of the parasite population. Factors that may influence the pattern of distribution of parasites, the relation between the level of parasite aggregation and the prevalence of infection, and changes in this level of aggregation as a function of host age are analysed. Factors which determine the diversity of species in parasite communities are presented, and aspects of exploitative and interference competition among parasites and their relations with biological control procedures are also considered. Attention is also focused on the regulatory and destabilizing processes influencing the dynamic behaviour of host-parasite population interactions.

Age Factors↗

PubMedDate not supplied

[Effects of nitrogen nutritional deficiency on the distribution of particular lipids in a eutrophic lake milieu].

The seasonal distribution of particulate lipids coupled with N-nutrient availability was studied in eutrophic Lake Aydat (Massif Central, France). The concentrations of lipids ranged between 196.9 and 2971.5 micrograms.l-1 (mean +/- s.d. = 1090.1 +/- 705.5 micrograms.l-1. Lipids were abundant in summer and fall when nitrates were insufficient reflecting thus an orientation of cell metabolism towards an accumulation of storage products. In such conditions, the heterocystous Cyanobacteria were found to develop due to their competitive advantage of exploiting atmospheric nitrogen. Their lipid metabolism did not seem to be affected at least partially by NO3- exhaustion.

Cyanobacteria↗

PubMed1984

A competitive binding assay for measurement of heparan sulfate in tissue digests.

Glycosaminoglycans complex with constituents of normal human serum, a finding that was exploited to develop a competitive binding assay for these substances. Heparan sulfate was isolated from renal cortex and radiolabeled with tritiated borohydride. The elution pattern of the radiolabeled material on Sephadex G-25, Bio-Gel P-30, and AG- 1X8 resin was identical to that of unlabeled heparan sulfate. The tritiated heparan sulfate formed radiolabeled precipitates when incubated with serum and zinc acetate. Binding was dose dependent and saturable. Heparin, heparan sulfate, and the chondroitin sulfates, but not hyaluronate or keratan sulfate, competed with the radiolabeled heparan sulfate for binding in a dose-dependent manner. The assay is specific for heparin polysaccharides in chondroitinase ABC-treated samples and is sensitive to microgram quantities.

Binding, Competitive↗

PubMed1974

Interference competition and niche theory.

A linear model of interspecific competition with separate parameters for exploitation and interference is deduced. Interference is assumed to have a cost and an effect. The interfering species realizes a "profit" if some resources, which the species interfered against would have utilized, are made available as a result of the interference. Interference is favored when its cost is small, its effect is high, and the resource overlap with the species interfered against is high. Interference is likely to be an alternative strategy to high exploitation efficiency. The incorporation of interference into niche theory clarifies the competitive phenomenon of unstable equilibrium points, excess density compensation on islands, competitive avoidance by escape in time and space, the persistence of the "prudent predator," and the magnitude of the difference between the size of a species' fundamental niche and its realized niche.

Adaptation, Biological↗

PubMed1993

Structure-activity relations of amiloride derivatives, acting as antagonists of cation binding on Na+/K(+)-ATPase.

In a search for an organic analogue of K+ or Na+ ions that binds to the cation binding sites of Na+/K(+)-ATPase with high affinity, the potency of the diuretic amiloride and its derivatives in blocking Rb+ occlusion has been tested. Although amiloride itself has a low affinity (> 200 microM), insertion of short alkyl chains in position 5 of the pyrazine ring of the molecule dramatically increased the affinity of the compound. For example, 5-(N-ethyl-N-isopropyl)amiloride (EIPA) competes with a Ki approximately 10 microM. In derivatives lacking a halogen in position 6 of the ring, a 6-fold decrease in affinity was found. Substitutions in the guanidinium moiety did not produce high affinity inhibitors of Rb+ occlusion. Several derivatives at positions 5 and 6 of the pyrazine ring were found to be strictly competitive inhibitors with respect to Rb+ ions. The highest affinity was observed around pH 8.0-8.2, and low temperature. EIPA and 5-(N-methyl-N-isobutyl)amiloride (MIBA) stabilized the E1 form of FITC1-labelled Na+/K(+)-ATPase, behaving as Na+ analogues. The present findings are similar to our previous results, showing that alkyl- and arylguanidinium derivatives are competitive Na(+)-like antagonists in cation sites. Conclusions concerning the structural features of amiloride derivatives which are necessary to produce the highest binding affinity, are being exploited in synthesis of competitive cation analogues. Derivatives with sufficiently high affinity (0.1-1 microM) will be converted to affinity and photoaffinity reagents.

Amiloride↗

PubMed2003

Stability of forest biodiversity.

Two hypotheses to explain potentially high forest biodiversity have different implications for the number and kinds of species that can coexist and the potential loss of biodiversity in the absence of speciation. The first hypothesis involves stabilizing mechanisms, which include tradeoffs between species in terms of their capacities to disperse to sites where competition is weak, to exploit abundant resources effectively and to compete for scarce resources. Stabilization results because competitors thrive at different times and places. An alternative, 'neutral model' suggests that stabilizing mechanisms may be superfluous. This explanation emphasizes 'equalizing' mechanisms, because competitive exclusion of similar species is slow. Lack of ecologically relevant differences means that abundances experience random 'neutral drift', with slow extinction. The relative importance of these two mechanisms is unknown, because assumptions and predictions involve broad temporal and spatial scales. Here we demonstrate that predictions of neutral drift are testable using palaeodata. The results demonstrate strong stabilizing forces. By contrast with the neutral prediction of increasing variance among sites over time, we show that variances in post-Glacial tree abundances among sites stabilize rapidly, and abundances remain coherent over broad geographical scales.

Computer Simulation↗

PubMed1998

Microbial transglutaminase-mediated synthesis of hapten-protein conjugates for immunoassays.

Hapten-protein conjugates are essential in many immunochemical assays, in particular, in assays employing titration or competitive assay formats. By exploitation of the catalytic properties of the microbial transglutaminase from Streptoverticillium mobarense sp. (MTGase), i.e., acyl transfer between gamma-carboxamide groups and various primary amines, new techniques for the synthesis of hapten-protein conjugates were developed. This is demonstrated by two examples. The feasibility of MTGase for hapten-protein conjugate synthesis was studied by coupling the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) to casein. Different procedures for the synthesis and the immobilization of these 2,4-D-casein conjugates were evaluated, comprising (i) a batch procedure, (ii) coupling of 2,4-D to an already immobilized layer of casein, and (iii) a method for simultaneous immobilization and conjugation. Kinetic studies revealed that conjugate formation in the batch procedure was almost complete after approx 2 h. By employing the conjugates in a competitive ELISA, detection limits as low as 0.05 microgram/L 2,4-D were reached. Using the approach with simultaneous immobilization and conjugation, the time for the whole assay could be reduced to only 2 h. Finally, to demonstrate the versatility of the enzymatic synthesis of hapten-protein conjugates, an ELISA for 2,4,6-trinitrotoluene (TNT) determination based on transglutaminase-synthesized conjugates was developed. In this assay, a detection limit as low as 0.04 microgram/l TNT was obtained.

2,4,5-Trichlorophenoxyacetic Acid↗

PubMed2004

Synthesis of hapten-protein conjugates using microbial transglutaminase.

Hapten-protein conjugates are essential in many immunochemical assays and in particular in assays using titration or competitive assay formats. By exploitation of the catalytic properties of the microbial transglutaminase from Streptoverticillium mobarense species (MTGase), that is, acyl transfer between gamma-carboxamide groups and various primary amines, new techniques for the enzymatic modification of proteins were developed. One example of bioconjugation is the biotinylation of antibodies for immunochemical applications using two species of activated biotin. In this case, the activated biotin acts as the acyl acceptor and is coupled to the glutamine residues of a monoclonal antibody. Because of the substrate specificity of the MTGase with regard to the limited number of glutamine residues and the surrounding microenvironment, only a limited number of binding sites on the target protein are available; the proposed method is thus particularly suitable when only a few biotin molecules need to be attached. Another example for the modification of proteins is the synthesis of hapten-protein conjugates used in competitive-type immunoassays. Methods for the synthesis of 2,4-D-casein conjugates (2,4-diclorophenoxyacetic acid, a herbicide) are presented. Various approaches, including a batch procedure and two in situ procedures, are described.

Bacterial Proteins↗

PubMed1984

Isolation of the nuclear yeast genes for citrate synthase and fifteen other mitochondrial proteins by a new screening method.

To isolate nuclear genes specifying imported mitochondrial proteins, a yeast genomic clone bank was screened by an RNA hybridization-competition assay. This assay exploited the fact that mRNAs for imported mitochondrial proteins are enriched in polysomes which are bound to the mitochondrial surface in cycloheximide-inhibited yeast cells. Clones selectively hybridizing to these enriched mRNAs were further screened by hybrid-selected translation and immunoprecipitation with monospecific antisera against individual mitochondrial proteins. Thirty-six clones were isolated which contained complete or partial copies of 16 different genes for imported mitochondrial proteins. Several of these clones caused expression of the corresponding precursor polypeptide in Escherichia coli or over-expression of the corresponding mature protein in yeast. The gene for the matrix enzyme citrate synthase was sequenced; the derived amino acid sequence of the precursor polypeptide revealed an amino-terminal extension containing basic but no acidic residues.

Amino Acid Sequence↗

PubMed2000

Canadian biotechnology start-ups, 1991-1997: the role of incumbents' patents and strategic alliances in controlling competition.

Fligstein (1996) contends that organizations act to exploit the institutional context in which they are embedded so as to stabilize the competition they face. Drawing on Fligstein's theoretical analysis, we conceptualize incumbent biotechnology firms' patent-ing and alliance-building activities as attempts to stabilize and control potential competition and analyze how these activities shape rates of founding in the Canadian biotechnology industry. We find that increases in the level and concentration of incumbents' patenting discourage founding, particularly in human application sectors of the industry where development and approval processes are more costly and time consuming. Incumbents' horizontal alliances depress start-ups; vertical alliances stimulate start-ups. Our findings highlight how technology appropriation and strategic alliances structure the competitive dynamics and evolution of high-technology, knowledge-intensive industries.

Biotechnology↗

PubMed2006

Incipient speciation through niche expansion: an example from the Arctic charr in a subarctic lake.

Two reproductive isolated morphs of Arctic charr (Salvelinus alpinus), termed profundal and littoral charr according to their different spawning habitats, co-occur in the postglacial lake Fjellfrøsvatn in North Norway. All profundal charr live in deep water their entire life and have a maximum size of 14cm, while the littoral charr grow to 40cm. Some small and young littoral charr move to the profundal zone in an ontogenetic habitat shift in the ice-free season and the rest of the population remains in epilimnic waters. The two morphs had different diet niches in the profundal zone: the profundal charr ate typical soft-bottom prey (chironomid larvae, pea mussels and benthic copepods), while the young littoral charr mainly consumed crustacean zooplankton. In four other lakes without a profundal morph (i.e. monomorphic populations), young charr also performed ontogenetic habitat shifts to the profundal zone and fed on zooplankton. The profundal morph of Fjellfrøsvatn therefore utilize a food resource niche that neither the littoral morph nor comparable monomorphic populations exploit. This suggests that intraspecific resource competition has driven incipient ecological speciation of the profundal charr of Fjellfrøsvatn. The exploitation of the soft-bottom resources by the profundal charr supports earlier experimental findings that the profundal morph is genetically different in trophic behaviour and morphology. The sympatric ecological divergence within the profundal habitat is possible because unexploited food resources (soft-bottom profundal prey) are available. Apparently, this represents a case of incipient segregation by expansion to new resource types (niche invasion), and not by subdivision of one broad ancestral niche.

Aging↗

PubMed2003

Social rank, feeding and winter weight loss in red deer: any evidence of interference competition?

During winter at northern latitudes, large herbivores often exploit patches of concentrated, relatively high quality forage, which may lead to interference competition. The factors affecting success in contests and subsequent dominance rank, such as age and body weight, remain key issues in ungulate behavioural ecology. Maternal effects on offspring body weight are well known, but few studies have investigated if mother's social rank influence offspring rank. Moreover, no study has related dominance rank in ungulates to weight loss during winter. Outcomes of social interactions (n=7,609), feeding time and spatial position in red deer (Cervus elaphus) hinds and calves, and weight loss of calves, were registered from 1981 to 1996 at six winter-feeding sites within the county of Sør-Trøndelag in Norway. The level of aggressiveness was higher among calves than among adult hinds, and the factors determining the outcome of contests also differed. The initiator won the majority of interactions (more than 90% in both hinds and calves). Social rank was related to both age and body weight in adult hinds, and related to body weight and mother rank in calves. The relationship between feeding time and rank was non-linear. Feeding time was correlated with rank only among high ranked hinds, while there was no such relationship among low ranked hinds or calves. There was no correlation between winter weight loss and social rank in calves. Our study therefore underlines that, although frequent aggression is observed at artificial feeding sites of northern herbivores, this is not necessarily sufficient to give rise to interference competition.

Age Factors↗

PubMedDate not supplied

Differential competitive inhibition: the theory of a concept.

The concept of differential competitive inhibition of cell surface isoenzymes is discussed. If the isoenzymes have different structures and functions it is likely that they will handle active site directed molecules at different rates. This could be tested by employing two competitive inhibitors in sequence and exploited if the second inhibitor is fluorescent. Two practical examples of this technique will be presented in the following manuscripts.

Binding, Competitive↗

PubMed1983

Inhibition by aphidicolin and dideoxythymidine triphosphate of a multienzyme complex of DNA synthesis from human cells.

A multienzyme complex consisting of DNA polymerase and several DNA precursor-synthesizing enzymes was solubilized by gentle lysis of cultured human cells. This complex channelled the distal precursor [3H]dTMP into DNA. The patterns of inhibition of the complex by aphidicolin and dideoxythymidine triphosphate (ddTTP) suggested that the complex contained the replicative DNA polymerase, polymerase alpha. Inhibition by ddTTP was competitive with dTTP. This was exploited to estimate the effective concentration of [3H]dTTP at the site of DNA synthesis during channelling of [3H]dTMP into DNA. The estimated concentration (about 50 microM) was so high as to suggest that the solubilized complex was able to functionally compartmentalize DNA precursors.

Aphidicolin↗

PubMed2003

Potent inhibition of ribonuclease A by oligo(vinylsulfonic acid).

Ribonuclease A (RNase A) can make multiple contacts with an RNA substrate. In particular, the enzymatic active site and adjacent subsites bind sequential phosphoryl groups in the RNA backbone through Coulombic interactions. Here, oligomers of vinylsulfonic acid (OVS) are shown to be potent inhibitors of RNase A that exploit these interactions. Inhibition is competitive with substrate and has Ki = 11 pm in assays at low salt concentration. The effect of salt concentration on inhibition indicates that nearly eight favorable Coulombic interactions occur in the RNase A.OVS complex. The phosphonic acid and sulfuric acid analogs of OVS are also potent inhibitors although slightly less effective. OVS is also shown to be a contaminant of MES and other buffers that contain sulfonylethyl groups. Oligomers greater than nine units in length can be isolated from commercial MES buffer. Inhibition by contaminating OVS is responsible for the apparent decrease in catalytic activity that has been observed in assays of RNase A at low salt concentration. Thus, OVS is both a useful inhibitor of RNase A and a potential bane to chemists and biochemists who use ethanesulfonic acid buffers.

Buffers↗

PubMed1998

Seeing difference: market health reform in Europe.

The comparative literature on health care reform has identified a convergence upon market models as nations respond to similar economic, technological, social, and demographic pressures. In this article I first challenge the conventional view by comparing "market" reforms of the late 1980s and early 1990s in the United Kingdom, the Netherlands, and Sweden. Though these nations did indeed converge upon the instrument of the market incentive, there was considerable divergence in the content and aims of their reform strategies. These nations designed their respective markets to make different tradeoffs among competing values. While all three exploited the principle of provider competition, they appointed different actors to judge the contest: the cost-conscious public authority in the United Kingdom, the quality-conscious patient in Sweden, and the optimizing consumer in the Netherlands. I argue that these countries were thus using common market tools to promote different health policy goals. Distinguishing these reforms further is the fact that--particularly in the Netherlands--there was a gap between market plans and the reality of implemented change. I then ask why nations responded so differently to such similar objective pressures. My contention is that this divergence reflects, in part, the different ideological orientations of the ruling party or coalition in each nation. Yet divergence is also the result of differences in both the design of political institutions and the structure of the pre-reform health system in each country.

Economic Competition↗

PubMed1996

The role of the human resources department in hospital reengineering.

The ¿people part¿ of reengineering is the most difficult to implement or even predict. In this context, active involvement by the Human Resources (HR) Department is a necessity, not an option, for the success of reengineering initiatives. Reengineering requires a changed environment and methods that HR must facilitate; creates extraordinary demands for leadership and communication, which HR is uniquely qualified to support; and represents an extraordinary opportunity for HR to reinvent its own processes and create a sustained competitive advantage for the organization. Exploiting these opportunities will require HR to proactively engage the organization.

Communication↗