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At least 325 records · Page 18Linked to original sources
PubMed2001

Spatial Patterns of Soil Microbial Communities in a Norway Spruce (Picea abies) Plantation.

The phospholipid fatty acid (PLFA) profiles of soil microbial communities were determined in relation to the patterns of tree cover in a mature Norway spruce plantation. Replicate samples of the surface organic layers were taken close to the trunk, at 1 m and at 2 m (under the edge of the canopy) beneath five trees. Samples were analyzed for standard PLFAs to assess the initial composition of the microbial communities. Replicate samples were then incubated under constant or fluctuating moisture conditions for 30 d to test the hypothesis that the patterns of microbial community structure (or its physiological state) might be determined by biophysical conditions under the tree canopies. The PLFA profiles near the trunks and at 2 m were similar, but samples taken 1 m from the bases of the trees contained lower concentrations of polyunsaturated (fungal) and monounsaturated PLFAs, and higher concentrations of saturated PLFAs. These differences in PLFA profiles were maintained during laboratory incubation under a regime of drying and wetting cycles, but there was some evidence of convergence in community structure under constant moisture conditions resulting from significant increases and decreases in specific bacterial PLFA concentrations. There were no effects of either moisture treatment on fungal PLFA concentrations. It is concluded that variation in the soil biophysical environment beneath the tree canopies resulted in the differentiation of spatially defined bacterial communities that were tolerant of moisture stress. The anomaly that differences in community structure were largest at an intermediate position of 1 m between the trunk and below the canopy edge was not explained but may relate to tree root distribution.

Journal Article↗
PubMed2003

The concept of multiple-nutrient-limited growth of microorganisms and its application in biotechnological processes.

The "law of the minimum" (Liebig's law) states that usually one nutrient restricts the maximum quantity of biomass that can be produced within a system, whereas all other nutrients are in excess. This general rule has been applied also to the growth of microorganisms, e.g., by adjusting the relative concentrations of the individual nutrients in growth media such that one of them, in the case of heterotrophic microbes, usually the carbon source, determines the maximum cell density that can be obtained in a culture. However, experimental data demonstrated that growth of microbial cultures can be limited simultaneously by two or more nutrients. These authors reported that during growth of bacteria and yeasts at a constant dilution rate in the chemostat, three distinct growth regimes were recognised as a function of the C:N ratio in the inflowing medium: (1) a clearly carbon-limited regime with the nitrogen source in excess, (2) a transition ("double-nutrient-limited") growth regime where both the carbon and the nitrogen source were below the detection limit, and (3) a clearly nitrogen-limited growth regime with the carbon source in excess. Subsequent calculations suggested that the extension and position of this double-nutrient-limited zone should be strongly dependent on the imposed growth rate: Whereas it is very narrow at high growth rates it should become very broad during slow growth. This pattern as a function of growth rate has now been confirmed for a number of different organisms. In industrial processes, microbial growth is always in some way controlled by the limited availability of nutrients, and limitation of specific nutrients is frequently used to force microbial cultures into a productive physiological state. This article will discuss what the consequences of multiple-nutrient-limited growth are for industrial processes and how the concept might be applied. Specific examples will be given that demonstrate the advantages and the potential of multiple nutrient-limited growth conditions for industrial production processes.

Bacteria↗
PubMed2007

The role of bacterial pathogens in cancer.

The association of Helicobacter pylori with gastric cancer is the best-studied relationship between a bacterial infection and cancer. Other bacterial pathogens in humans and rodents are now being recognized as potentially having a direct role in carcinogenesis. Thus, it might be possible to understand the pathogenesis and prevention of certain cancers by studying the bacterial infections associated with them, and their effects on the host. However, the mechanisms by which bacteria contribute to cancer formation are complex, and recent investigations show that they involve the interplay between chronic inflammation, direct microbial effects on host cell physiology and, ultimately, changes in tissue stem cell homeostasis.

Animals↗
PubMed2004

Complement: a unique innate immune sensor for danger signals.

The complement (C) inflammatory cascade is part of the phylogenetically ancient innate immune response and is crucial to our natural ability to ward off infection. It has three critical physiologic activities: (i) defending against microbial infections by triggering the generation of a membranolytic complex (C5b9 complex) at the surface of the pathogen and C fragments (named opsonins, i.e., C1q, C3b and iC3b) which interact with C cell surface receptors (CR1, CR3 and CR4) to promote phagocytosis. Soluble C anaphylatoxins (C4a, C3a and C5a) greatly control the local pro-inflammatory response through the chemotaxis and activation of leukocytes; (ii) bridging innate and adaptive immunity (essentially through C receptor type 2, CR2, expressed by B cells) and (iii) disposing of immune complexes and the products of the inflammatory injury (i.e., other danger signals, e.g., toxic cell debris and apoptotic corpses) to ensure the protection and healing of the host. The regulatory mechanisms of C are finely balanced so that, on the one hand, the deposition of C is focused on the surface of invading microorganisms and, on the other hand, the deposition of C on normal cells is limited by several key C inhibitors (e.g., CD46, CD55 and CD59). Knowledge of the unique molecular and cellular innate immunological interactions that occur in the development and resolution of pathology should facilitate the design of effective therapeutic strategies to fight selectively against intruders.

Animals↗
PubMed2002

Helicobacter pylori and gastrointestinal tract adenocarcinomas.

Although gastric adenocarcinoma is associated with the presence of Helicobacter pylori in the stomach, only a small fraction of colonized individuals develop this common malignancy. H. pylori strain and host genotypes probably influence the risk of carcinogenesis by differentially affecting host inflammatory responses and epithelial-cell physiology. Understanding the host-microbial interactions that lead to neoplasia will improve cancer-targeted therapeutics and diagnostics, and provide mechanistic insights into other malignancies that arise within the context of microbially initiated inflammatory states.

Adenocarcinoma↗
PubMed2001

Hpt, a bacterial homolog of the microsomal glucose- 6-phosphate translocase, mediates rapid intracellular proliferation in Listeria.

Efficient replication in vivo is essential for a microparasite to colonize its host and the understanding of the molecular mechanisms by which microbial pathogens grow within host tissues can lead to the discovery of novel therapies to treat infection. Here we present evidence that the foodborne bacterial pathogen Listeria monocytogenes, a facultative intracellular parasite, exploits hexose phosphates (HP) from the host cell as a source of carbon and energy to fuel fast intracellular growth. HP uptake is mediated by Hpt, a bacterial homolog of the mammalian translocase that transports glucose-6-phosphate from the cytosol into the endoplasmic reticulum in the final step of gluconeogenesis and glycogenolysis. Expression of the Hpt permease is tightly controlled by the central virulence regulator PrfA, which upon entry into host cells induces a set of virulence factors required for listerial intracellular parasitism. Loss of Hpt resulted in impaired listerial intracytosolic proliferation and attenuated virulence in mice. Hpt is the first virulence factor to be identified as specifically involved in the replication phase of a facultative intracellular pathogen. It is also a clear example of how adaptation to intracellular parasitism by microbial pathogens involves mimicry of physiological mechanisms of their eukaryotic host cells.

Amino Acid Sequence↗
PubMed1997

The metabolic importance of unabsorbed dietary lipids in the colon.

Digestion and absorption of lipids is a highly efficient process. From Western diets about 95% will be absorbed. This implies that together with lipids from endogenous sources 6-8 g of lipids will enter the colon daily. This input significantly increases during various lipid malabsorption syndromes. It has long been assumed that the biological fate of unabsorbed lipids is physiologically not relevant. However, significant microbial lipid metabolism occurs. Circumstantial evidence is arising which supports a role of unabsorbed lipid metabolites in the development of colonic diseases. Lipid metabolites may act as detergents in the colon, leading to mucosal injury and reactive hyperproliferation, which in its turn could promote tumour development. Lipid metabolites could also be transformed in biological active metabolites, which have a tumour promoting potency. More mechanistic information is needed on the colonic metabolic fate of lipids in order to develop strategies for manipulating colonic flora in the prevention of lipid related colonic diseases.

Colon↗
PubMed2001

Cloning, purification, crystallization and preliminary crystallographic analysis of Bacillus subtilis LuxS.

LuxS of Bacillus subtilis is a member of a novel family of proteins with a potential role in quorum sensing, controlling important aspects of cellular physiology in a range of microbial species. B. subtilis luxS was cloned, expressed in Escherichia coli, purified and crystallized using the hanging-drop method of vapour diffusion with ammonium sulfate as the precipitant. The crystals belong to one of the enantiomorphic space groups P6(1)22 or P6(5)22, with approximate unit-cell parameters a = b = 63.6, c = 151.5 A and one subunit in the asymmetric unit, corresponding to a packing density of 2.5 A(3) Da(-1). The crystals diffract X-rays to at least 1.55 A resolution on a synchrotron-radiation source. Determination of the structure will provide insights into the key determinants of function of this class of proteins, for which no structures are currently available.

Bacillus subtilis↗
PubMed1993

In situ identification of bacteria in drinking water and adjoining biofilms by hybridization with 16S and 23S rRNA-directed fluorescent oligonucleotide probes.

Free-water-phase and surface-associated microorganisms from drinking water were detected and roughly identified by hybridization with fluorescence-labeled oligonucleotide probes complementary to regions of 16S and 23S rRNA characteristic for the domains Bacteria, Archaea, and Eucarya and the beta and gamma subclasses of Proteobacteria. Samples of glass-attached biofilms and plankton were taken from a Robbins device installed in a water distribution system. More than 70% of the surface-associated cells and less than 40% of the planktonic cells visualized by 4',6-diamidino-2-phenylindole staining bound detectable amounts of rRNA-targeted probes. These findings are an indication for higher average rRNA content and consequently higher physiological activity of the attached microbial cells compared with the free-living cells. All detectable cells hybridized with the bacterial probe, whereas no Archaea and no Eucarya cells could be detected. Simultaneous hybridization with probes specific for the beta and gamma subclasses of Proteobacteria revealed that microcolonies already consisted of mixed populations in early stages with fewer than 50 cells. These observations provide further evidence that the coexistence and interaction of bacteria in drinking water biofilms may be an integral part of their growth and survival strategies.

Bacteria↗
PubMed1998

Spatial physiological heterogeneity in Pseudomonas aeruginosa biofilm is determined by oxygen availability.

The role of oxygen availability in determining the local physiological activity of Pseudomonas aeruginosa growing in biofilms was investigated. Biofilms grown in an ambient-air environment expressed approximately 1/15th the alkaline phosphatase specific activity of planktonic bacteria subjected to the same phosphate limitation treatment. Biofilms grown in a gaseous environment of pure oxygen exhibited 1.9 times the amount of alkaline phosphatase specific activity of air-grown biofilms, whereas biofilms grown in an environment in which the air was replaced with pure nitrogen prior to the inducing treatment did not develop alkaline phosphatase activity. Frozen cross sections of biofilms stained for alkaline phosphatase activity with a fluorogenic stain demonstrated that alkaline phosphatase activity was concentrated in distinct bands adjacent to the gaseous interfaces. These bands were approximately 30 micron thick with biofilms grown in air, 2 micron thick with biofilms grown in pure nitrogen, and 46 micron thick with biofilms grown in pure oxygen. Overall biofilm thickness ranged from approximately 117 to approximately 151 micron. Measurements with an oxygen microelectrode indicated that oxygen was depleted locally within the biofilm and that the oxygen-replete zone was of a dimension similar to that of the biologically active zone, as indicated by alkaline phosphatase induction. These experiments revealed marked spatial physiological heterogeneity within P. aeruginosa biofilms in which active protein synthesis was restricted by oxygen availability to the upper 30 micron of the biofilm. Such physiological heterogeneity has implications for microbial ecology and for understanding the reduced susceptibilities of biofilms to antimicrobial agents.

Adenosine Triphosphatases↗
PubMedDate not supplied

Thionins from Viscum album L: influence of the viscotoxins on the activation of granulocytes.

BACKGROUND: Extracts from European mistletoe (Viscum album L.) are applied in adjuvant cancer treatment, and some components, especially the mistletoe lectins (ML) have been immunologically characterised, but not the thionins, termed viscotoxins (VT). MATERIALS AND METHODS: The influence of the VT on human granulocytes was studied by flow cytometry: E.coli co-stimulated respiratory burst by oxidation of dihydrorhodamine 123 to rhodamine 123 and phagocytosis by ingestion of FITC-labelled E.coli. RESULTS: VT (25 and 250 micrograms/ml), in contrast to ML, significantly enhanced phagocytosis and burst activity. VT-rich mistletoe extracts also exerted significant effects. In addition, E.coli-activated granulocytes positively stain with Annexin-V and propidium iodide only due to 250 micrograms/ml VT incubation, suggesting that at this concentration burst activity was induced by the physiological activity of granulocytes after microbial ingestion and also by cytotoxic effects. CONCLUSION: Viscotoxins exert yet unknown strong immunomodulatory effects on human granulocytes, which might be of benefit for tumour patients, in addition to their cytotoxic properties.

Adjuvants, Immunologic↗
PubMed2003

In situ growth of the novel SM1 euryarchaeon from a string-of-pearls-like microbial community in its cold biotope, its physical separation and insights into its structure and physiology.

Recently, a unique archaeal/bacterial community that grows in a macroscopically visible string-of-pearls-like structure in cold (~10 degrees C), sulfurous marsh water was discovered. Here, a new technique is described that allows the fast and reliable growth of these string-of-pearls-like microbial communities in larger quantities on polyethylene nets in nature. The microbial net population, estimated to consist of about 10,000 single pearls, can be harvested once a week and the archaeal cells selectively separated by density gradient centrifugation. As in native pearls, the archaeal cell fraction obtained consisted of a single type of coccoid cells only, 0.6 micro m in diameter. This novel type of euryarchaea has been tentatively named SM1 euryarchaeon. Electron microscopy and immuno-fluorescence in situ hybridization (immuno-FISH) revealed that about 100 pili-like fibers, up to 3 micro m in length, emanate radially from the surface of each cell. The SM1 euryarchaeal cells exhibited a viability of about 90%. The optimal conditions for viability were temperatures between -2 degrees C and 20 degrees C, pH 5-9, and low salt conditions; cell viability was independent of oxygen partial pressures. The cultures stained gram-positive, the cell wall was sensitive to SDS, EDTA and Proteinase K treatment. The cells did not exhibit the typical fluorescence for methanogens and did not contain coenzyme F(420). The G+C-content was 34.5 mol%.

Archaea↗
PubMed2003

Seasonal population changes in the restriction fragment length polymorphism (RFLP) patterns from PCR-amplified 16S rRNA genes of predominant ribotypes in microbial mat samples from the Ebro Delta (Spain).

The stratified benthic microbial communities, which developed as a consequence of the physico-chemical gradients and the physiology of the inhabiting microorganisms, from Ebro Delta microbial mats were analyzed. 16S rRNA eubacterial and archaeal genes were amplified by polymerase chain reaction (PCR). PCR products were separately digested with three different restriction enzymes (AluI, HinfI, and RsaI) and later separated by horizontal electrophoresis to determine whether changes of predominant ribotypes are occurring over a period of a year. Comparison of total restriction patterns was performed by scoring similarities by using the Jaccard coefficient and then building a multidimensional scaling (MDS) map from the resulting similarities matrix. The three enzymes gave a consistent result, a seasonal distribution instead of a spatial and/or physiological one.

Archaea↗
PubMed2003

Recent advances in petroleum microbiology.

Recent advances in molecular biology have extended our understanding of the metabolic processes related to microbial transformation of petroleum hydrocarbons. The physiological responses of microorganisms to the presence of hydrocarbons, including cell surface alterations and adaptive mechanisms for uptake and efflux of these substrates, have been characterized. New molecular techniques have enhanced our ability to investigate the dynamics of microbial communities in petroleum-impacted ecosystems. By establishing conditions which maximize rates and extents of microbial growth, hydrocarbon access, and transformation, highly accelerated and bioreactor-based petroleum waste degradation processes have been implemented. Biofilters capable of removing and biodegrading volatile petroleum contaminants in air streams with short substrate-microbe contact times (<60 s) are being used effectively. Microbes are being injected into partially spent petroleum reservoirs to enhance oil recovery. However, these microbial processes have not exhibited consistent and effective performance, primarily because of our inability to control conditions in the subsurface environment. Microbes may be exploited to break stable oilfield emulsions to produce pipeline quality oil. There is interest in replacing physical oil desulfurization processes with biodesulfurization methods through promotion of selective sulfur removal without degradation of associated carbon moieties. However, since microbes require an environment containing some water, a two-phase oil-water system must be established to optimize contact between the microbes and the hydrocarbon, and such an emulsion is not easily created with viscous crude oil. This challenge may be circumvented by application of the technology to more refined gasoline and diesel substrates, where aqueous-hydrocarbon emulsions are more easily generated. Molecular approaches are being used to broaden the substrate specificity and increase the rates and extents of desulfurization. Bacterial processes are being commercialized for removal of H(2)S and sulfoxides from petrochemical waste streams. Microbes also have potential for use in removal of nitrogen from crude oil leading to reduced nitric oxide emissions provided that technical problems similar to those experienced in biodesulfurization can be solved. Enzymes are being exploited to produce added-value products from petroleum substrates, and bacterial biosensors are being used to analyze petroleum-contaminated environments.

Aerobiosis↗
PubMed2000

Variation of Microbial Rhizosphere Communities in Response to Crop Species, Soil Origin, and Inoculation with Sinorhizobium meliloti L33.

A greenhouse study with soil-plant microcosms was conducted in order to compare the effect of crop species, soil origin, and a bacterial inoculant on the establishment of microbial communities colonizing plant roots. Two crop species, alfalfa (Medicago sativa) and rye (Secale cereale), were grown separately in two soils collected from agricultural fields at different locations and with differing histories of leguminous crop rotation. A subset of microcosms was inoculated at 10(6) cfu g(-1) soil with the luciferase marker gene-tagged Sinorhizobium meliloti strain L33, a symbiotic partner of M. sativa. Microbial consortia were collected from the rhizospheres of alfalfa after 10 weeks of incubation and from rye after 11 weeks. S. meliloti L33 populations were one to two orders of magnitude higher in the rhizospheres of alfalfa than of rye. In soil with previous alfalfa cultivation, 80% of the alfalfa nodules were colonized by indigenous bacteria, while in the other soil alfalfa was colonized almost exclusively (>90%) with S. meliloti L33. Three community-level targeting approaches were used to characterize the variation of the extracted microbial rhizosphere consortia: (1) Community level physiological profiles (CLPP), (2) fatty acid methyl ester analysis (FAME), and (3) diversity of PCR amplified 16S rRNA target sequences from directly extracted ribosomes, determined by temperature gradient gel electrophoresis (TGGE). All approaches identified the crop species as the major determinant of microbial community characteristics. Consistently, the influence of soil was of minor importance, while a modification of the alfalfa-associated microbial community structure after inoculation with S. meliloti L33 was only consistently observed by using TGGE.

Journal Article↗
PubMed1999

Laboratory selection for the comparative physiologist.

An increasingly popular experimental approach in comparative physiology is to study the evolution of physiological traits in the laboratory, using microbial, invertebrate and vertebrate models. Because selective conditions are well-defined, selected populations can be replicated and unselected control populations are available for direct comparison, strong conclusions regarding the adaptive value of an evolved response can be drawn. These studies have shown that physiological systems evolve rapidly in the laboratory, but not always as one would expect from comparative studies of different species. Laboratory environments are often not as simple as one thinks, so that the evolution of behavioral differences or selection acting on different life stages can lead to unanticipated results. In some cases, unexpected responses to laboratory selection may suggest new insights into physiological mechanisms, which might not be available using other experimental approaches. I outline here recent results (including success stories and caveats for the unwary investigator) and potential directions for selection experiments in comparative physiology.

Adaptation, Physiological↗
PubMed1991

[Effect of microbial immunomodulators on the course of lymphocytic choriomeningitis virus infection in old mice with physiological thymus involution].

Aged mice with physiological thymus involution were treated intraperitoneally with 0.2 ml of live Newcastle Disease Virus (NDV) containing attenuated NDV vaccine (HA titre: log 2(16)/ml) one day before or with Mannozym (0.1% zymosan suspension) four days and one day before intracerebral inoculation with 100 LD50 dose of LCMV. One dose of M was equal to 40 mg/kg zymosan. Both, NDV vaccine and M pretreatments contributed to the development of fatal lymphocytic choriomeningitis, thus enhanced the cellular immune response to LCMV infection. Present results are compared with earlier results which were attained on young adult suckling mice in similar system with pretreatment with different microbial immunomodulators. Present results reinforced the authors' earlier observations that the direction and degree of immunomodulatory effects can be influenced by the actual conditions, like age, of the immune system.

Adjuvants, Immunologic↗
PubMed1989

Direct differential counting compared with testing of isolates as means of assessing hydrolytic capacities of natural microbial populations.

The abundance of microorganisms with characteristic, physiological activities in aquatic sediment communities can be estimated either by direct differential counting on selective media or by making isolations followed by testing of the isolates. The two methods have been compared with regard to microorganisms performing hydrolyses of different compounds. The first method was used to examine the effect of a model ecocontaminant on the hydrolytic activities of the sediment population.

Colony Count, Microbial↗