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At least 1,351 records · Page 75Linked to original sources
PubMed1998

Mechanism of action of the antimicrobial peptide buforin II: buforin II kills microorganisms by penetrating the cell membrane and inhibiting cellular functions.

The mechanism of action of buforin II, which is a 21-amino acid peptide with a potent antimicrobial activity against a broad range of microorganisms, was studied using fluorescein isothiocyanate (FITC)-labeled buforin II and a gel-retardation experiment. Its mechanism of action was compared with that of the well-characterized magainin 2, which has a pore-forming activity on the cell membrane. Buforin II killed Esche-richia coli without lysing the cell membrane even at 5 times minimal inhibitory concentration (MIC) at which buforin II reduced the viable cell numbers by 6 orders of magnitude. However, magainin 2 lysed the cell to death under the same condition. FITC-labeled buforin II was found to penetrate the cell membrane and accumulate inside E. coli even below its MIC, whereas FITC-labeled magainin 2 remained outside or on the cell wall even at its MIC. The gel-retardation experiment showed that buforin II bound to DNA and RNA of the cells over 20 times strongly than magainin 2. All these results indicate that buforin II inhibits the cellular functions by binding to DNA and RNA of cells after penetrating the cell membranes, resulting in the rapid cell death, which is quite different from that of magainin 2 even though they are structurally similar: a linear amphipathic alpha-helical peptide.

Anti-Bacterial Agents↗
PubMed1999

Integrin-like proteins in Candida spp. and other microorganisms.

The vertebrate integrins provide a paradigm for cell surface proteins involved in adhesion and morphogenesis. However, homologs of integrins have been found in more primitive organisms. This review will discuss the evidence for surface proteins in Candida albicans and Candida tropicalis that contain motifs reminiscent of integrins and will analyze the contributions of one of these proteins, Int1p, to adhesion, morphogenesis, and virulence. Other microorganisms thought to express integrin-like proteins will also be addressed.

Animals↗
PubMed2000

Control strategies for the polarotactic orientation of the microorganism Euglena gracilis.

A simple mathematical model for the signal received by the dichroic photoreceptor molecules in the motile alga, Euglena gracilis, when irradiated by polarized light, is described and used to test hypotheses for the control strategies employed by the microorganism during negative phototaxis. The model is used to analyse and explain the experimental results of Häder (1987. Arch. Microbiol.147, 179-183).

Animals↗
PubMed2000

Flow cytometric analysis of microorganisms.

The application of flow cytometry to microorganisms is as old as the technique itself, but it has historically been underexploited for microbial applications. This is now being reversed and microbiologists are ideally placed to benefit from recent technological advances. While earlier papers demonstrated the use of flow cytometry for studies of viability and taxonomy, recent developments in bioinformatics and reporter gene technologies are leading to novel applications in microbiology. Variants of green fluorescent protein have been used for the study of conditional microbial gene regulation in medically important host-pathogen interactions and fluorescence-activated cell sorting is being applied to the isolation of novel mutants in directed evolution studies. This paper reviews the reasons for the delay in the application of flow cytometry to microbial problems, the range of applications, and their limitations and considers the progress made in developing new strategies for use in microbiological investigations.

Bacteria↗
PubMed1997

Pentachlorophenol dermal absorption and disposition from soil in swine: effects of occlusion and skin microorganism inhibition.

Residue of the environmentally relevant biocide pentachlorophenol (PCP) is found mainly in soil, making dermal contact one of the primary routes for PCP exposure. To quantify exposure effects on dermal absorption and systemic disposition, [14C-UL]PCP was dosed nonocclusively or occlusively at 40 micrograms/cm2 in a soil-based mixture in an in vivo swine model. Additionally, antibiotics were also codosed with occlusive PCP in soil to examine the impacts of skin microbial PCP biodegradation on total dermal absorption. Under nonocclusive, occlusive, and occlusive-antibiotic conditions, total radiolabel absorption by 408 hr was 29.08, 100.72, and 86.21% dose, respectively. Tissue accumulation of PCP and its labeled metabolite(s) was very significant in swine since one-half to two-thirds of the absorbed dose was still present in tissues by 17 days after PCP dermal exposure. High 14C concentrations were found in liver, kidney, lung, ovary, and uterus. Urine and fecal routes were equally important for label excretion from the body. Occlusion enhanced total dermal absorption and changed the shape of the absorption profiles in the blood and plasma. Skin microorganism inhibition retarded 14C dermal absorption, altered local and systemic tissue distribution, and increased plasma/blood concentration ratios, suggesting skin microbial PCP degradation might play an important role in the altered absorption and disposition by occlusion. This study demonstrated significant dermal absorption and extensive tissue persistence of PCP after soil exposure. Occlusion and skin microflora growth may greatly impact dermal absorption, cutaneous disposition, and systemic toxic input. Therefore, exposure-specific PCP absorption and disposition profiles must be taken into consideration in risk analysis.

Animals↗
PubMed1999

Polyhydroxybutyrate: plastic made and degraded by microorganisms.

Polyhydroxybutyrate (PHB) offers many advantages over traditional petrochemically derived plastics. In addition to its complete biodegradability, PHB is formed from renewable resources. It possesses better physical properties than polypropylene for food packaging applications and is completely nontoxic. The poor low-impact strength of PHB is solved by incorporation of hydroxyvalerate monomers into the polymer to produce polyhydroxybutyrate-co-valerate (PHBV), which is commercially marketed under the trade name Biopol. Like PHB, PHBV completely degrades into carbon dioxide and water under aerobic conditions. Microbial synthesis of PHB is the best method for industrial production because it ensures the proper stereochemistry for biodegradation. Microorganisms synthesize and store PHB under nutrient-limited conditions and degrade and metabolize it when the limitation is removed. Current production employs Alcaligenes eutrophus because it grows efficiently on glucose as a carbon source, accumulates PHB up to 80% of its dry weight, and is able to synthesize PHBV when propionic acid is added to the feedstock. PHBV is currently 16 times the price of polypropylene. However, the development of transgenic PHA-producing organisms is expected to greatly reduce its cost. Benefits of using transgenic systems include lack of a depolymerase system, ability to use faster-growing organisms, production of highly purified polymers, and ability to utilize inexpensive carbon sources. Because transgenic plants may someday result in the evolution of plastic crops that could lower the price of PHA to a competitive level, future research will surely focus on such recombinant DNA techniques.

Bacteria↗
PubMed1996

Fluorescence decay of tryptophans in serine proteinases from microorganisms: relation to X-ray models.

Fluorescence decay kinetics of indole groups in five proteinases from microorganisms are reported. The data show differences between the excited state lifetimes of the tryptophans located in identical positions in the polypeptide chains of the closely related proteinases mesentericopeptidase and subtilisin Novo. The lifetime of the single Trp 113 in subtilisins DY and Carlsberg are identical. The microenvironments of this residue in the four subtilisins are identical and probably its fluorescence is quenched in these proteins. The crystallographic models of the enzymes investigated were analysed in the region of the tryptophyl residues and provide an explanation for the observed emission properties.

Bacillus↗
PubMed1993

Hazards from pathogenic microorganisms in land-disposed sewage sludge.

Sewage sludge is a complex mixture of organic and inorganic compounds of biological and mineral origin that are precipitated from wastewater and sewage during primary, secondary, and tertiary sewage treatment. Present in these sludges are significant numbers of microorganisms that include viral, bacterial, protozoan, fungal, and helminth pathogens. The treatment of sludge to reduce biochemical oxygen demand, solids content, and odor is not always effective in reducing numbers of pathogens. This becomes a public health concern because the infectious dose for some of these pathogens may be as low as 1 particle (virus) to 50 organisms (Giardia). When sludge is applied to land for agricultural use and landfill compost, these pathogens can survive from days (bacteria) to months (viruses) to years (helminth eggs), depending on environmental conditions. Shallow aquifers can become contaminated with pathogens from sludge and, depending on groundwater flow, these organisms may travel significant distances from the disposal site. Communities that rely on groundwater for domestic use can become exposed to these pathogens, leading to a potential disease outbreak. Currently, methods to determine the risk of disease from pathogens in land-disposed sludge are inadequate because the sensitivity of pathogen detection is poor. The application of recombinant DNA technology (gene probes and polymerase chain reaction) to environmental samples may provide increased sensitivity for detecting specific pathogens in land-disposed sludge and greatly improved risk assessment models for our exposure to these sources of pathogens.

Hazardous Waste↗
PubMed1991

Trends in research related to the influence of "water activity" on microorganisms in food.

The use of humectants and drying to make foods safe and stable has been one of the underlying principles of food preservation for centuries. With the more recent discovery that the ratio of water vapor pressure to that of pure water (aw) is a useful parameter when related to microbial growth and other stabilizing factors in foods, a valuable means of predicting stability factors based on water limitation has become available. Microorganisms have been categorized with respect to their capacity to grow and produce metabolites in various conditions of limited aw. In addition, the metabolic basis for microbial inhibition has now been determined and schemes for its genetic control have been uncovered. The implications that these discoveries have in a wide variety of applications are far-reaching.

Bacteria↗
PubMed1995

Characterization of two proteinase inhibitor (ATI) cDNAs from alfalfa leaves (Medicago sativa var. Vernema): the expression of ATI genes in response to wounding and soil microorganisms.

cDNAs encoding two Bowman-Birk proteinase inhibitors were isolated from the leaves of alfalfa (Medicago sativa). The cDNAs are derived from a small gene family (3 to 10 genes) encoding alfalfa trypsin inhibitors (ATIs). Each cDNA clone encoded a mature ATI that was part of a larger, putative preprotein. ATI mRNAs are continuously expressed in flower parts, but are mechanically wound-inducible in the stems and leaves. ATI mRNA is shown to be continuously present in roots of soil-grown plants, but its presence is primarily in response to microorganisms present in the soil. Additionally, while mechanical wounding of the alfalfa roots induced ATI mRNA synthesis both in the roots and in the leaves, microbial infection of the roots triggered ATI mRNA synthesis in the roots but not in the leaves. These results suggest that both local and systemic signalling pathways for proteinase inhibitor synthesis are present in alfalfa plants.

Amino Acid Sequence↗
PubMed1990

Physiology of aliphatic hydrocarbon-degrading microorganisms.

This paper reviews aspects of the physiology and biochemistry of the microbial biodegradation of alkanes larger than methane, alkenes and alkynes with particular emphasis upon recent developments. Subject areas discussed include: substrate uptake; metabolic pathways for alkenes and straight and branched-chain alkanes; the genetics and regulation of pathways; co-oxidation of aliphatic hydrocarbons; the potential for anaerobic aliphatic hydrocarbon degradation; the potential deployment of aliphatic hydrocarbon-degrading microorganisms in biotechnology.

Anaerobiosis↗
PubMed1990

Formation and physiological role of biosurfactants produced by hydrocarbon-utilizing microorganisms. Biosurfactants in hydrocarbon utilization.

Microbial growth on water-insoluble carbon sources such as hydrocarbons is accompanied by metabolic and structural alterations of the cell. The appearance of surface-active compounds (biosurfactants) in the culture medium or attached to the cell boundaries is often regarded as a prerequisite for initial interactions of hydrocarbons with the microbial cell. Under this point of view, biosurfactants produced by hydrocarbon-utilizing microorganisms, their structures and physico-chemical properties are reviewed. The production of such compounds is mostly connected with growth limitation in the late logarithmic and the stationary growth phase, in which specific enzymes are induced or derepressed. Addition of purified biosurfactants to microbial cultures resulted in inhibitory as well as in stimulatory effects on growth. Therefore, a more differentiated view of microbial production of surface-active compounds is proposed. Biosurfactants should not only be regarded as prerequisites of hydrocarbon uptake, but also as secondary metabolic products.

Bacteria↗
PubMed1996

Susceptibility of microorganisms isolated from chronic suppurative otitis media to ciprofloxacin.

In order to evaluate the susceptibility of the microorganisms isolated from chronic suppurative otitis media to ciprofloxacin, cultures of specimens from 127 patients with chronic suppurative otitis media and their antibiotic sensitivity results were examined. The most common aerobic isolates were Pseudomonas sp., Proteus sp., and Staphylococcus aureus with recovery rates of 40.7%, 21.6% and 19.1% respectively. Sensitivity results showed that 6.2% of Pseudomonas isolates, 2.9% of Proteus isolates, 10% of Staphylococcus aureus isolates and 8.3% of Escherichia coli isolates were resistant to ciprofloxacin.

Anti-Infective Agents↗
PubMed1990

Growth stimulation of Treponema denticola by periodontal microorganisms.

Previous experiments have indicated that enrichment of subgingival plaque in human serum can lead to the accumulation of Treponema denticola. T. denticola depends on bacterial interactions for its growth in serum. Aim of the present study was to identify specific microorganisms involved in the growth stimulation of T. denticola. To this end, strains isolated from previous plaque enrichment cultures were tested for growth stimulation in co-cultures with T. denticola. In addition, growth of T. denticola was tested in culture filtrates of the same strains, Bacteroides intermedius, Eubacterium nodatum, Veillonella parvula and Fusobacterium nucleatum were found to enhance growth of T. denticola in co-cultures. A continuous co-culture of T. denticola, F. nucleatum and B. intermedius in human serum gave very high levels of T. denticola, up to 3.10(9).ml-1. Mechanisms involved in growth stimulation may include the ability of B. intermedius and E. nodatum to cleave the protein-core of serum (glyco-)proteins, making these molecules accessible for degradation by T. denticola. In addition, E. nodatum was found to produce a low-molecular weight growth-factor for T. denticola, that was heat-stable and acid as well as alkaline resistant. V. parvula may provide peptidase activities complementary to those of T. denticola. The nature of the growth enhancing activity of F. nucleatum is yet unknown. The data support the dependency of T. denticola on other bacterial species for growth in the periodontal pocket.

Amino Acid Sequence↗
PubMed1986

Acetyl-coenzyme A: arylamine N-acetyltransferases in microorganisms: screening and isolation of an enzyme from Bacillus cereus.

The raw extracts of a series of microorganisms were screened for the presence of acetyl-coenzyme A: arylamine N-acetyltransferase (AAAT) using a radioactive assay with 3H-acetyl-coenzyme A and aniline as substrates. Enzyme activities were primarily detected in the soluble fractions of Bacillus and Nocardia species, and in some further soil organisms. Only strains of Bacillus cereus were able to acetylate 4-nitroaniline and 3,5-dimethyl-4-nitroaniline. The fermentation conditions for the production of the enzyme were optimized. The AAAT from one strain of Bacillus cereus was purified 24-fold and characterized.

Acetyl Coenzyme A↗
PubMed1988

Flow cytometric screening and isolation of Escherichia coli clones which express surface antigens of the oil-degrading microorganism Acinetobacter calcoaceticus RAG-1.

Flow cytometry (FCM) in conjunction with immunocytochemical-labeling was used to analyze and screen a population of Escherichia coli clones containing a genomic library from the oil-degrading microorganism Acinetobacter calcoaceticus RAG-1 surface antigens. Reconstruction experiments using mixed populations indicated that RAG-1 cells could be clearly distinguished at a ratio of one RAG-1 cell to 500 Escherichia coli cells. Using this technique two clones, WM143 and WM191, were isolated and shown by restriction endonuclease cleavage and Southern hybridization to contain plasmids carrying inserts of RAG-1 DNA of 9.4 and 9.8 kb respectively.

Acinetobacter↗
PubMed1981

Clostridium aceticum (Wieringa), a microorganism producing acetic acid from molecular hydrogen and carbon dioxide.

Spores of Clostridium aceticum (Wieringa) from 1947 have been revived, and a study for a redescription of this microorganism has been carried out. C. aceticum was Gram negative. The cells were rodshaped and peritrichously flagellated. Round spores were formed in terminal position. The DNA contained 33 mol % guanine plus cytosine. The organism was obligately anaerobic and grew either chemolithotrophically with H2 + CO2 or chemoorganotrophically with compounds such as fructose, L-glutamate, L-malate or pyruvate. H2 and CO2 were converted to acetic acid according to the following equation: 2CO2 + 4H2 leads to CH3COOH + 2H2O The optimal temperature for growth was 30 degrees C. The optimal pH for chemolithotrophic growth was 8.3. The doubling times for chemolithotrophic and chemoorganotrophic growth were 25 and 8 h, respectively.

Acetates↗
PubMed1987

The molecular genetics of C1 utilizing microorganisms. An overview.

The availability of recombinant DNA techniques has enabled the successful genetic analysis and manipulation of a range of C1 utilizing microorganisms. It has resulted in the identification of genes of interest on both plasmids and the chromosome; enabled the linkage of chromosomal genes to be determined; established the function and regulatory patterns of genes essential for utilization of C1 compounds and provided information on the evolution of methanogenic bacteria.

Bacteria↗