Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “microbial competition”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed2004

[Research advance in polyphosphate-accumulating microorganisms in enhanced biological phosphorus removal process].

This paper discussed the function of enhanced biological phosphorus removal (EBPR) in P pollution control, P containing wastewater treatment and P resources recovery, and summarized the metabolic characteristics, research progress and methodologies of polyphosphate-accumulating organisms (PAOs). Although polyphosphate has been found in many organisms, only few of PAOs were isolated, cultured and identified. Culture medium formulation is the key to isolate PAOs and to study the microbial accumulation of polyphosphate, and the competition of glycogen-accumulating organisms (GAOs) with PAOs for carbon resources is one of the reasons of low EBPR efficiency. Modern scientific methods such as fluorescent in situ hybridization, confocal laser scanning microscope, microautoradiography, and in vivo NMR spectroscopy, provided powerful tools to analyze PAO species composition, spatial structure and functional properties under field conditions. The knowledge of PAO is valuable to enhance the P removal efficiency in water treatment plant, and to improve our understanding on P transformation and transferring in environment.

Bacteria↗
PubMedDate not supplied

The use of concanavalin A to competitively inhibit Pseudomonas aeruginosa adherence to rabbit corneal epithelium.

Microbial adherence to corneal epithelial cells is the initial step in the development of infectious keratitis. In an attempt to inhibit this process, we evaluated the effects of concanavalin A (Con A) upon the adherence of Pseudomonas aeruginosa to injured rabbit corneal epithelial cells. A sterile 21-gauge needle was used to create linear epithelial injuries. Identical samples from suspensions of a pure strain of P. aeruginosa were placed on two groups of injured corneas. Prior to bacterial application, one group of corneas received topical application of Con A, a lectin that is capable of binding to alpha-D-mannose or alpha-D-glucose. The animals were sacrificed 1 hour after application of the bacteria. Scanning electron microscopy of the excised corneas revealed that, compared to the corneas that had not been exposed to Con A, those exposed to the lectin had significant fewer adherent P. aeruginosa bacilli. Additionally, only rare bacteria were noted adhering to the uninjured superficial epithelial cells. These results suggest that, by competitively binding to the exposed mannose and/or glucose groups on the surfaces of these cells, Con A is capable of inhibiting the adherence of P. aeruginosa to injured epithelial cells.

Animals↗
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↗
PubMed1996

Two-step degradation of pyrene by white-rot fungi and soil microorganisms.

The effect of soil microorganisms on mineralization of 14C-labelled pyrene by white-rot fungi in solid-state fermentation was investigated. Two strains of white-rot fungi, Dichomitus squalens and a Pleurotus sp., were tested. The fungi were incubated on milled wheat straw contaminated with [14C]pyrene for 15 weeks. CO2 and 14CO2 liberated from the cultures were determined weekly. To study the effect of soil microorganisms on respiration and [14C]pyrene mineralization in different periods of fungal development, the fungal substrate was covered with soil at different times of incubation (after 0, 1, 3, 5, 7, 9 or 11 weeks). The two fungi showed contrasting ecological behaviour in competition with the soil microflora. Pleurotus sp. was highly resistant to microbial attack and had the ability to penetrate the soil. D. squalens was less competitive and did not colonize the soil. The resistance of the fungus was dependent on the duration of fungal preincubation. Mineralization of [14C]pyrene by mixed cultures of D. squalens and soil microorganisms was higher than by the fungus or the soil microflora alone when soil was added after 3 weeks of incubation or later. With Pleurotus sp., the mineralization of [14C]pyrene was enhanced by the soil microflora irrespective of the time of soil application. With D. squalens, which in pure culture mineralized less [14C]pyrene than did Pleurotus sp., the increase of [14C]pyrene mineralization caused by soil application was higher than with Pleurotus sp.

Antibiosis↗
PubMed2000

Are microorganisms more effective than plants at competing for nitrogen?

Plant scientists have long debated whether plants or microorganisms are the superior competitor for nitrogen in terrestrial ecosystems. Microorganisms have traditionally been viewed as the victors but recent evidence that plants can take up organic nitrogen compounds intact and can successfully acquire N from organic patches in soil raises the question anew. We argue that the key determinants of 'success' in nitrogen competition are spatial differences in nitrogen availability and in root and microbial distributions, together with temporal differences in microbial and root turnover. Consequently, it is not possible to discuss plant-microorganism competition without taking into account this spatiotemporal context.

Fungi↗
PubMed1999

Microbial antagonism: a neglected avenue of natural products research.

Competition amongst microbes for space and nutrients in the marine environment is a powerful selective force which has led to the evolution of a variety of effective strategies for colonising and growing on surfaces. We are particularly interested in the chemical ecology of marine epibiotic bacteria which live on the surfaces of marine algae or invertebrates. Over 400 strains of surface-associated bacteria from various species of seaweed and invertebrate from Scottish coastal waters were isolated and 35% of them shown to produce antimicrobial compounds. This is a much higher proportion than free living marine isolates or soil bacteria. In addition, many strains which did not normally produce antibiotics could be induced to do so by exposing them to small amounts of live cells, supernatants from other bacterial cultures or other chemicals. Thus the number of strains able to produce antibiotics appears to be much higher than previously thought. Induction of antibiotic production was elicited by other marine epibionts and also by terrestrial human pathogens such as Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa. An understanding of this type of chemical induction and the factors regulating non-constitutive secretion of antimicrobial compounds will allow more effective strategies for searching for new chemotherapeutic antibiotics to be designed.

Acinetobacter↗
PubMed1984

Adherence of cervical, vaginal and distal urethral normal microbial flora to human uroepithelial cells and the inhibition of adherence of gram-negative uropathogens by competitive exclusion.

The adherence of the normal flora to human uroepithelial cells was examined using scanning and transmission electron microscopy and an in vitro adhesion assay. The normal flora were isolated from human cervical, vaginal and distal urethral surfaces. Human uroepithelial cells were obtained from healthy females (controls) and from female patients with recurrent urinary tract infection. The results indicate that: 1) there was no significant difference between the mean adherence of the normal flora to the uroepithelial cells from controls or patients, but there were quantitative differences between different bacterial species of the normal flora attaching to uroepithelial cells; 2) bacterial species isolated from the distal urethral and vaginal surfaces attached in larger numbers to uroepithelial cells from controls than from patients at day 10 of the menstrual cycle (peak value of adherence); 3) the adherence patterns of the cervical and vaginal microbial flora were bicyclic and appeared to be related to the human menstrual cycle; 4) complete or partial inhibition of adherence of several Gram-negative uropathogens was achieved by preincubating the uroepithelial cells with several bacterial species of the normal flora. Results from this study suggest that the normal flora of the urinary tract may play an important protective role against attachment of uropathogens to the surfaces of uroepithelial cells, and that the blocking capacity of these organisms may vary over the menstrual cycle.

Cervix Uteri↗
PubMed1992

Genetics of competition for nodulation of legumes.

An economically important problem in microbial ecology concerns the efficacy of rhizobial inoculants for the formation of nitrogen-fixing root nodules on legume crop plants such as soybean, alfalfa, and clover. Some strains of rhizobia can increase symbiotic nitrogen fixation under controlled conditions. However, attempts to improve nitrogen fixation under agricultural conditions with such strains often fail, usually as a result of the presence of indigenous rhizobia limiting nodulation by the inoculum strains. This problem is referred to as the Rhizobium competition problem, and molecular genetics is being used to address the problem from two perspectives. First, the host specificity of rhizobia is being characterized with the long term goal of developing strains that can nodulate a very strain-specific host-legume genotype. Second, the genetic basis of competitiveness in several strains is being examined. Genetic determinants of nodulation competitiveness have been isolated and mechanisms for their stable integration into the genome of superior nitrogen-fixing strains have been developed. Several phenotypes have been identified as playing an important role in nodulation competitiveness including antibiosis, motility, speed of nodulation, cell-surface characteristics, and nodulation efficiency. Several solutions to this problem are likely to result from these strategies and will be useful for certain legumes in specific locations.

Fabaceae↗
PubMed1975

Competitive ability of amylolytic bacteria in activated sludge.

Shifts were induced into the microbial community of activated sludge by the pulse addition of soluble starch. The subsequent changes of amylolytic and proteolytic microbial populations were recorded. Four amylolytic strains were isolated and characterized with regard to carrying capacity, specific surface and growth kinetics. The competitive ability of these strains was studied by means of two-member competition experiments. These experiments were analysed according to the Lotka-Volterra model and the de Wit method. The different results obtained suggest that the dominance of the amylolytic Pseudomonas sp. (code 01) is based on a combined occurrence of high amylolytic activity, large relative cell surface, high maximum specific growth rate and reduced sensitivity towards associated proteolytic populations.

Aeromonas↗
PubMed2003

Life under nutrient limitation in oligotrophic marine environments: an eco/physiological perspective of Sphingopyxis alaskensis (formerly Sphingomonas alaskensis).

The oceans of the world are nutrient-limited environments that support a dynamic diversity of microbial life. Heterotrophic prokaryotes proliferate in oligotrophic regions and affect nutrient transformation and remineralization thereby impacting directly on the all marine biota. An important challenge in studying the microbial ecology of oligotrophic environments has been the isolation of ecologically important species. This goal has been recognized not only for its relevance in defining the dynamics of community composition, but for enabling physiological studies of competitive species and inferring their impact on the microbial food web. This review describes the successful isolation attempts of the ultramicrobacterium, Sphingopyxis alaskensis (formerly described as Sphingomonas alaskensis) using extinction dilution culturing methods. It then provides a comprehensive perspective of the unique physiological and genetic properties that have been identified that distinguish it from typical copiotrophic species. These properties are described through studies of the growth phase and growth rate control of macromolecular synthesis, stress resistance and global gene expression (proteomics). We also discuss the importance of integrating ecological and physiological approaches for studying microorganisms in marine environments.

Alaska↗
PubMed2004

Convenient determination of DNA extraction efficiency using an external DNA recovery standard and quantitative-competitive PCR.

Molecular biology techniques have advanced the field of microbial ecology through the analysis of nucleic acids. Most techniques that use DNA or RNA require their extraction from environmental matrices, which can be tedious and inefficient. While a number of extraction methods, both laboratory-based and commercially available, have been developed, none of these include a convenient method to determine extraction efficiency. We have developed an external DNA recovery standard, Lambda DNA (target DNA) contained within pBR322, allowing routine determinations of DNA recovery efficiency. Target DNA was added to sediments as whole cells, total DNA extracted using commercial DNA extraction/purification kits and the amount of target DNA recovered quantified by quantitative-competitive PCR (QC-PCR). Three commercially available kits (UltraClean Soil DNA, FastDNA SPIN and Soil Master DNA Extraction) were evaluated for recovery efficiency. Recoveries for the three kits ranged from undetectable to 43.3% with average recoveries of 14.9+/-16.0%, 28.3+/-10.5% and 2.4+/-0.1% (UltraClean, FastDNA and Soil Master, respectively). Quantification of target DNA proved robust in sediments heavily polluted with polycyclic aromatic hydrocarbons and the external recovery standard could be detected following extraction and amplification from as few as 1 x 10(3) cells added to 0.5 g sediment (wet weight). The external DNA recovery standard was also added directly to the sediment as purified plasmid DNA prior to extraction. It was recovered with similar efficiency as when added as whole cells, suggesting its usefulness in estimating DNA recovery in ribosomal DNA studies. These results show that, while the commercial kits offer expedited sample processing, the extraction efficiencies vary on a sample-by-sample basis and were <100%. Therefore, quantitative DNA studies require an estimation of DNA recovery.

Bacteriophage lambda↗
PubMed1998

Evolution of competitive fitness in experimental populations of E. coli: what makes one genotype a better competitor than another?

An important problem in microbial ecology is to identify those phenotypic attributes that are responsible for competitive fitness in a particular environment. Thousands of papers have been published on the physiology, biochemistry, and molecular genetics of Escherichia coli and other bacterial models. Nonetheless, little is known about what makes one genotype a better competitor than another even in such well studied systems. Here, we review experiments to identify the phenotypic bases of improved competitive fitness in twelve E. coli populations that evolved for thousands of generations in a defined environment, in which glucose was the limiting substrate. After 10,000 generations, the average fitness of the derived genotypes had increased by approximately 50% relative to the ancestor, based on competition experiments using marked strains in the same environment. The growth kinetics of the ancestral and derived genotypes showed that the latter have a shorter lag phase upon transfer into fresh medium and a higher maximum growth rate. Competition experiments were also performed in environments where other substrates were substituted for glucose. The derived genotypes are generally more fit in competition for those substrates that use the same mechanism of transport as glucose, which suggests that enhanced transport was an important target of natural selection in the evolutionary environment. All of the derived genotypes produce much larger cells than does the ancestor, even when both types are forced to grow at the same rate. Some but not all, of the derived genotypes also have greatly elevated mutation rates. Efforts are now underway to identify the genetic changes that underlie those phenotypic changes, especially substrate specificity and elevated mutation rate for which there are good candidate loci. Identification and subsequent manipulation of these genes may provide new insights into the reproducibility of adaptive evolution, the importance of co-adapted gene complexes, and the extent to which distinct phenotypes (e.g., substrate specificity and cell size) are affected by the same mutations.

Adaptation, Physiological↗
PubMed2004

Creation of a shikimate pathway variant.

The competition between the Escherichia coli carbohydrate phosphotransferase system and 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase for phosphoenolpyruvate limits the concentration and yield of natural products microbially synthesized via the shikimate pathway. To circumvent this competition for phosphoenolpyruvate, a shikimate pathway variant has been created. 2-Keto-3-deoxy-6-phosphogalactonate (KDPGal) aldolases encoded by Escherichia coli dgoA and Klebsiella pneumoniae dgoA are subjected to directed evolution. The evolved KDPGal aldolase isozymes exhibit 4-8-fold higher specific activities relative to that for native KDPGal aldolase with respect to catalyzing the condensation of pyruvate and d-erythrose 4-phosphate to produce DAHP. To probe the ability of the created shikimate pathway variant to support microbial growth and metabolism, growth rates and synthesis of 3-dehydroshikimate are examined for E. coli constructs that lack phosphoenolpruvate-based DAHP synthase activity and rely on evolved KDPGal aldolase for biosynthesis of shikimate pathway intermediates and products.

Aldehyde-Lyases↗
PubMed2001

Use of Metabolic Inhibitors to Characterize Ecological Interactions in an Estuarine Microbial Food Web.

Understanding microbial food web dynamics is complicated by the multitude of competitive or interdependent trophic interactions involved in material and energy flow. Metabolic inhibitors can be used to gain information on the relative importance of trophic pathways by uncoupling selected microbial components and examining the net effect on ecosystem structure and function. A eukaryotic growth inhibitor (cycloheximide), a prokaryotic growth inhibitor (antibiotic mixture), and an inhibitor of photosynthesis (DCMU) were used to examine the trophodynamics of microbial communities from the tidal creek in North Inlet, a salt marsh estuary near Georgetown, South Carolina. Natural microbial communities were collected in the spring, summer, and fall after colonization onto polyurethane foam substrates deployed in the tidal creek. Bacterial abundance and productivity, heterotrophic ciliate and flagellate abundance, and phototrophic productivity, biomass, and biovolume were measured at five time points after inhibitor additions. The trophic responses of the estuarine microbial food web to metabolic inhibitors varied with season. In the summer, a close interdependency among phototrophs, bacteria, and protozoa was indicated, and the important influence of microzooplanktonic nutrient recycling was evident (i.e., a positive feedback loop). In the fall, phototroph and bacteria interactions were competitive rather than interdependent, and grazer nutrient regeneration did not appear to be an important regulatory factor for bacterial or phototrophic activities. The results indicate a seasonal shift in microbial food web structure and function in North Inlet, from a summer community characterized by microbial loop dynamics to a more linear trophic system in the fall. This study stresses the important role of microbial loops in driving primary and secondary production in estuaries such as North Inlet that are tidally dominated by fluctuations in nutrient supply and a summer phytoplankton bloom.

Journal Article↗
PubMed2004

DNA vaccines to attack cancer.

Delivery of antigens by injection of the encoding DNA allows access to multiple antigen-presenting pathways. Knowledge of immunological processes can therefore be used to modify construct design to induce selected effector functions. Expression can be directed to specific intracellular sites, and additional genes can be fused or codelivered to amplify responses. Therapeutic vaccination against cancer adds a requirement to overcome tolerance and to activate a weakened immune repertoire. Induction of CD4(+) T helper cells is critical for both antibody and T cell effector responses. To activate immunity against tumor antigens, we fused the tumor-derived sequences to genes encoding microbial proteins. This strategy engages T helper cells from the large antimicrobial repertoire for linked help for inducing antibody against cell-surface tumor antigens. The principle of linked T cell help also holds for induction of epitope-specific antitumor CD8(+) T cells, but the microbial sequence has to be minimized to avoid competition with tumor antigens. Epitope-specific DNA vaccination leads to powerful antitumor attack and can activate immunity from a profoundly tolerized repertoire. Vaccine designs validated in preclinical models are now in clinical trial with immune responses detected against both tumor antigens and fused microbial antigens. DNA priming is highly efficient, but boosting may benefit from increased antigen expression. Physical methods including electroporation provide increased expression without introducing additional competing antigens. A wide range of cancers can be targeted, and objective assays of response will determine efficacy.

Animals↗
PubMed1995

Coexistence of three competing microbial populations in a chemostat with periodically varying dilution rate.

Coexistence of three microbial populations engaged in pure and simple competition is not possible in a chemostat with time-invariant operating conditions under any circumstances. It is shown that by periodic variation of the chemostat dilution rate it is possible to obtain a stable coexistence state of all three populations in the chemostat. This is accomplished by performing a numerical bifurcation analysis of a mathematical model of the system and by determining its dynamic behavior with respect to its operating parameters. The coexistence state obtained in the periodically operated chemostat is usually periodic, but cases of quasi-periodic and chaotic behavior are also observed.

Bacteria↗
PubMed2005

Bacteriophages--potential for application in wastewater treatment processes.

Bacteriophages are viruses that infect and lyse bacteria. Interest in the ability of phages to control bacterial populations has extended from medical applications into the fields of agriculture, aquaculture and the food industry. Here, the potential application of phage techniques in wastewater treatment systems to improve effluent and sludge emissions into the environment is discussed. Phage-mediated bacterial mortality has the potential to influence treatment performance by controlling the abundance of key functional groups. Phage treatments have the potential to control environmental wastewater process problems such as: foaming in activated sludge plants; sludge dewaterability and digestibility; pathogenic bacteria; and to reduce competition between nuisance bacteria and functionally important microbial populations. Successful application of phage therapy to wastewater treatment does though require a fuller understanding of wastewater microbial community dynamics and interactions. Strategies to counter host specificity and host cell resistance must also be developed, as should safety considerations regarding pathogen emergence through transduction.

Bacteria↗
PubMed2005

Determination of microbial carbon sources in petroleum contaminated sediments using molecular 14C analysis.

Understanding microbial carbon sources is fundamental to elucidating the role of microbial communities in carbon cycling and in the biodegradation of organic contaminants. Because the majority of anthropogenic contaminants are either directly or indirectly derived from fossil fuels that are devoid of 14C, radiocarbon can be used as a natural inverse tracer of contaminant carbon in the contemporary environment. Here, 14C analysis of individual microbial phospholipid fatty acids (PLFA) was used to characterize the carbon sources utilized bythe active microbial community in salt marsh sediments contaminated by the Florida oil spill of 1969 in Wild Harbor, West Falmouth, MA. A specific goal was to determine whether this community is actively degrading petroleum residues that persist in these sediments. The delta14C values of microbial PLFA in all sediment horizons (contaminated and noncontaminated) matched the delta14C of the total sedimentary organic carbon after petroleum removal, indicating that no measurable metabolism of petroleum residues was occurring. This result agrees with ancillary data such as the delta13C content and distribution of PLFA, and the residual hydrocarbon composition determined by comprehensive two-dimensional gas chromatography (GCxGC) analysis. We hypothesize that microbes have chosen to respire the natural organic matter rather than the residual petroleum hydrocarbons because the former is more labile. Future efforts directed at determining indices of microbial degradation of petroleum hydrocarbons should consider competition with natural organic matter.

Accidents↗