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J Sørensen

Publications and source records attributed to J Sørensen.

At least 19 recordsLinked to original sources
PubMed2002

Impact of biocontrol strain Pseudomonas fluorescens CHA0 on rhizosphere bacteria isolated from barley (Hordeum vulgare L.) with special reference to Cytophaga-like bacteria.

AIMS: To assess the impact of the biocontrol strain Pseudomonas fluorescens CHA0 on a collection of barley rhizosphere bacteria using an agar plate inhibition assay and a plant microcosm, focusing on a CHA0-sensitive member of the Cytophaga-like bacteria (CLB). METHODS AND RESULTS: The effect of strain CHA0 on a collection of barley rhizosphere bacteria, in particular CLB and fluorescent pseudomonads sampled during a growth season, was assessed by a growth inhibition assay. On average, 85% of the bacteria were sensitive in the May sample, while the effect was reduced to around 68% in the July and August samples. In the May sample, around 95% of the CLB and around 45% of the fluorescent pseudomonads were sensitive to strain CHA0. The proportion of CHA0-sensitive CLB and fluorescent pseudomonad isolates decreased during the plant growth season, i.e. in the July and August samples. A particularly sensitive CLB isolate, CLB23, was selected, exposed to strain CHA0 (wild type) and its genetically modified derivatives in the rhizosphere of barley grown in gnotobiotic soil microcosms. Two dry-stress periods were imposed during the experiment. Derivatives of strain CHA0 included antibiotic or exopolysaccharide (EPS) overproducing strains and a dry-stress-sensitive mutant. Despite their inhibitory activity against CLB23 in vitro, neither wild-type strain CHA0, nor any of its derivatives, had a major effect on culturable and total cell numbers of CLB23 during the 23-day microcosm experiment. Populations of all inoculants declined during the two dry-stress periods, with soil water contents below 5% and plants reaching the wilting point, but they recovered after re-wetting the soil. Survival of the dry-stress-sensitive mutant of CHA0 was most affected by the dry periods; however, this did not result in an increased population density of CLB23. CONCLUSIONS: CLB comprise a large fraction of barley rhizosphere bacteria that are sensitive to the biocontrol pseudomonad CHA0 in vitro. However, in plant microcosm experiments with varying soil humidity conditions, CHA0 or its derivatives had no major impact on the survival of the highly sensitive CLB strain, CLB23, during two dry-stress periods and a re-wetting period; all co-existed well in the rhizosphere of barley plants. SIGNIFICANCE AND IMPACT OF THE STUDY: Results indicate a lack of interaction between the biocontrol pseudomonad CHA0 and a sensitive CLB when the complexity increases from agar plate assays to plant microcosm experiments. This suggests the occurrence of low levels of antibiotic production and/or that the two bacterial genera occupy different niches in the rhizosphere.

Bacteriological Techniques↗
PubMed2002

Antibiotic and biosurfactant properties of cyclic lipopeptides produced by fluorescent Pseudomonas spp. from the sugar beet rhizosphere.

Cyclic lipopeptides (CLPs) with antibiotic and biosurfactant properties are produced by a number of soil bacteria, including fluorescent Pseudomonas spp. To provide new and efficient strains for the biological control of root-pathogenic fungi in agricultural crops, we isolated approximately 600 fluorescent Pseudomonas spp. from two different agricultural soils by using three different growth media. CLP production was observed in a large proportion of the strains (approximately 60%) inhabiting the sandy soil, compared to a low proportion (approximately 6%) in the loamy soil. Chemical structure analysis revealed that all CLPs could be clustered into two major groups, each consisting of four subgroups. The two major groups varied primarily in the number of amino acids in the cyclic peptide moiety, while each of the subgroups could be differentiated by substitutions of specific amino acids in the peptide moiety. Production of specific CLPs could be affiliated with Pseudomonas fluorescens strain groups belonging to biotype I, V, or VI. In vitro analysis using both purified CLPs and whole-cell P. fluorescens preparations demonstrated that all CLPs exhibited strong biosurfactant properties and that some also had antibiotic properties towards root-pathogenic microfungi. The CLP-producing P. fluorescens strains provide a useful resource for selection of biological control agents, whether a single strain or a consortium of strains was used to maximize the synergistic effect of multiple antagonistic traits in the inoculum.

Agriculture↗
PubMed2001

Cyclic lipoundecapeptide amphisin from Pseudomonas sp. strain DSS73.

The crystal structure of the lipoundecapeptide amphisin, presented here as the tetrahydrate, C(66)H(114)N(12)O(20).4H(2)O, originating from non-ribosomal biosynthesis by Pseudomonas sp. strain DSS73, has been solved to a resolution of 0.65 A. The primary structure of amphisin is beta-hydroxydecanoyl-D-Leu-D-Asp-D-allo-Thr-D-Leu-D-Leu-D-Ser-L-Leu-D-Gln-L-Leu-L-Ile-L-Asp (Leu is leucine, Asp is aspartic acid, Thr is threonine, Ser is serine, Gln is glutamine and Ile is isoleucine). The peptide is a lactone, linking Thr4 O(gamma) to the C-terminal. The stereochemistry of the beta-hydroxy acid is R. The peptide is a close analogue of the cyclic lipopeptides tensin and pholipeptin produced by Pseudomonas fluorescens. The structure of amphisin is mainly helical (3(10)-helix), with the cyclic peptide wrapping around a hydrogen-bonded water molecule. This lipopeptide is amphiphilic and has biosurfactant and antifungal properties.

Bacterial Proteins↗
PubMed2001

Axonal elongation through long acellular nerve segments depends on recruitment of phagocytic cells from the near-nerve environment. Electrophysiological and morphological studies in the cat.

The distal nerve stump plays a central role in the regeneration of peripheral nerve but the relative importance of cellular and humoral factors is not clear. We have studied this question by freezing the tibial nerve distal to a crush lesion in cat. The importance of constituents from the near-nerve environment was assessed by modification of the contact between the tibial nerve and the environment. Silicone cuffs, containing electrodes for electrophysiological assessment of nerve regeneration, were placed around the tibial nerve distal to the crush site. The interaction between long acellular frozen nerve segments (ANS) and the near-nerve environment was ascertained by breaching the silicone cuff to allow access of cellular or humoral components. Tibial nerves were crushed and frozen for 40 mm and enclosed in nerve cuffs with 0.45-microm holes or 2.0-mm holes to allow access of humoral factors or tissue ingrowth, respectively. In a second set of experiments, tibial nerves were crushed and either frozen for 20+20 mm, leaving a 10 mm segment with viable cells in the center (stepping-stone segment) or frozen for 50 mm. These nerves were enclosed in cuffs with 2.0 mm holes corresponding to the viable nerve segment. The regeneration was monitored electrophysiologically by implanted electrodes and after 2 months the nerves were investigated by light and electron microscopy. The results indicate that soluble substances in the near-nerve environment, such as nutrients, oxygen or tropic substances did not exert any independent beneficial effect on the outgrowing axons. However, phagocytic cells entering the acellular segment from the near-nerve environment were crucial for axonal outgrowth in long ANS.

Animals↗
PubMed2001

[Diagnostic benefit of gastrointestinal endoscopy in infants under one year of age--a two-year survey].

INTRODUCTION: Gastrointestinal endoscopy in children is a well-established procedure. We reviewed our experience of endoscopy in infants below one year of age to evaluate indications, endoscopic findings, histology, and complications. MATERIAL AND METHODS: Twenty-eight infants were studied over a two-year period. Of these, 18 underwent upper endoscopy, six recto/sigmoidoscopy or colonoscopy, and four both procedures. RESULTS: The most common indication (10/22) for upper endoscopy was vomiting and suspicion of gastrooesophageal reflux disease. In these infants, 24-hour continuous monitoring of the oesophageal pH followed the procedure. Indications for lower endoscopy were rectal bleeding (n = 6) and intractable diarrhoea (n = 4). There were no complications to anaesthesia, endoscopy, or biopsy. Overall, there were endoscopic abnormalities in 82% and histological abnormalities in 75% of the infants. The diagnostic findings included rare disorders, such as eosinophilic gastroenteritis, microvillous inclusion disease, and chylomicron retention disease. Diagnosis of these diseases requires gastrointestinal biopsy. DISCUSSION: Gastrointestinal endoscopy is a safe procedure, which is a valuable part of the diagnostic work-up in a selected group of infants with long-lasting or severe gastrointestinal symptoms.

Colonoscopy↗
PubMed2001

Economic evaluation of multidisciplinary pain management in chronic pain patients: a qualitative systematic review.

In this qualitative systematic review, we have evaluated studies of the economic effectiveness of multidisciplinary pain treatment in chronic non-malignant pain patients. Published reports were identified from a systematic search of bibliographic databases (MEDLINE and EMBASE) and reference lists of retrieved reports. Fourteen reports of nine studies of patients suffering from back pain, fibromyalgia, and mixed chronic pain conditions were considered to be appropriate as economic analyses. In the selected studies, we found serious methodological problems in study designs and application of outcome measures. The quality of the cost measurements was characterized by an apparent lack of tradition using economic methodology. This review does not give an answer to whether multidisciplinary pain management in chronic pain patients is cost-effective or not. Application of standard methods of costing and outcome measurement are essential before studies of cost-effectiveness in multidisciplinary pain treatment can be used in decision-making and planning.

Chronic Disease↗
PubMed2001

Toxic effects of linear alkylbenzene sulfonate on metabolic activity, growth rate, and microcolony formation of Nitrosomonas and Nitrosospira strains.

Strong inhibitory effects of the anionic surfactant linear alkylbenzene sulfonate (LAS) on four strains of autotrophic ammonia-oxidizing bacteria (AOB) are reported. Two Nitrosospira strains were considerably more sensitive to LAS than two Nitrosomonas strains were. Interestingly, the two Nitrosospira strains showed a weak capacity to remove LAS from the medium. This could not be attributed to adsorption or any other known physical or chemical process, suggesting that biodegradation of LAS took place. In each strain, the metabolic activity (50% effective concentration [EC(50)], 6 to 38 mg liter(-1)) was affected much less by LAS than the growth rate and viability (EC(50), 3 to 14 mg liter(-1)) were. However, at LAS levels that inhibited growth, metabolic activity took place only for 1 to 5 days, after which metabolic activity also ceased. The potential for adaptation to LAS exposure was investigated with Nitrosomonas europaea grown at a sublethal LAS level (10 mg liter(-1)); compared to control cells, preexposed cells showed severely affected cell functions (cessation of growth, loss of viability, and reduced NH(4)(+) oxidation activity), demonstrating that long-term incubation at sublethal LAS levels was also detrimental. Our data strongly suggest that AOB are more sensitive to LAS than most heterotrophic bacteria are, and we hypothesize that thermodynamic constraints make AOB more susceptible to surfactant-induced stress than heterotrophic bacteria are. We further suggest that AOB may comprise a sensitive indicator group which can be used to determine the impact of LAS on microbial communities.

Alkanesulfonic Acids↗
PubMed2000

Viscosinamide-producing Pseudomonas fluorescens DR54 exerts a biocontrol effect on Pythium ultimum in sugar beet rhizosphere.

Growth inhibition of the root pathogen Pythium ultimum by the biocontrol agent Pseudomonas fluorescens DR54 inoculated on sugar beet seeds was studied in a soil microcosm. Plant emergence was followed, together with bacterial rhizosphere colonization, antibiotic production and effects on fungal growth. P. fluorescens DR54 inoculation of the P. ultimum-challenged seeds improved plant emergence after 7 days compared to a control without the biocontrol strain. At this time, P. fluorescens DR54 was the dominating colony-forming pseudomonad in rhizosphere soil samples from inoculated seedlings as shown by immuno-staining with a strain specific antibody. Viscosinamide, a cyclic lipopeptide, which has previously been identified as a major antagonistic determinant produced by P. fluorescens DR54 and shown to induce physiological changes in P. ultimum in vitro, could be detected in the rhizosphere samples. The impact of P. fluorescens DR54 on the growth and activity of P. ultimum was studied by direct microscopy after staining with the vital fluorescent dyes Calcofluor white and fluorescein diacetate. P. fluorescens DR54 caused reduction in P. ultimum mycelial density, oospore formation and intracellular activity. Further, Pythium oospore formation was absent in the presence of P. fluorescens DR54. A striking effect on zoospore-forming indigenous fungi was also observed in microcosms with P. fluorescens DR54 and, thus, where viscosinamide could be detected; a large number of encysted zoospores were seen in such microcosms both with and without P. ultimum infections. In vitro studies confirmed that purified viscosinamide induced encystment of Pythium zoospores.

Journal Article↗
PubMed2000

Simultaneous detection of the establishment of seed-inoculated Pseudomonas fluorescens strain DR54 and native soil bacteria on sugar beet root surfaces using fluorescence antibody and in situ hybridization techniques.

Colonization at sugar beet root surfaces by seedling-inoculated biocontrol strain Pseudomonas fluorescens DR54 and native soil bacteria was followed over a period of 3 weeks using a combination of immunofluorescence (DR54-targeting specific antibody) and fluorescence in situ hybridization (rRNA-targeting Eubacteria EUB338 probe) techniques with confocal laser scanning microscopy. The dual staining protocol allowed cellular activity (ribosomal number) to be recorded in both single cells and microcolonies of strain DR54 during establishment on the root. After 2 days, the population density of strain DR54 reached a constant level at the root basis. From this time, however, high cellular activity was only found in few bacteria located as single cells, whereas all microcolony-forming cells occurring in aggregates were still active. In contrast, a low density of strain DR54 was observed at the root tip, but here many of the bacteria located as single cells were active. The native population of soil bacteria, comprising a diverse assembly of morphologically different forms and size classes, initiated colonization at the root basis only after 2 days of incubation. Hence the dual staining protocol allowed direct microscopic studies of early root colonization by both inoculant and native soil bacteria, including their differentiation into active and non-active cells and into single or microcolony-forming cells.

Journal Article↗
PubMed2000

Direct microscopy of bacillus endospore germination in soil microcosms.

Antagonistic endospore-forming Bacillus spp. offer a large potential as seed inoculants for control of soil-borne pathogens. In the soil, however, inoculated Bacillus endospores may remain dormant without germination, and plant protection can therefore be inefficient and unpredictable. A method based on direct fluorescence microscopy in soil microcosms was used to determine whether low-cost organic additives incorporated into seed coating material could stimulate endospore germination. Complex organic additives supported a high level of endospore germination of the fungal antagonist Paenibacillus polymyxa CM5-5. Skim milk is a low-cost additive that may be incorporated into seed coating material for efficient induction of Bacillus endospore germination in soil.

Alanine↗
PubMed2000

Structure, production characteristics and fungal antagonism of tensin - a new antifungal cyclic lipopeptide from Pseudomonas fluorescens strain 96.578.

AIM: To study the antagonistic activity by Pseudomonas fluorescens strain 96.578 on the plant pathogenic fungus Rhizoctonia solani. METHODS AND RESULTS: Strain 96.578 produced a new cyclic lipopeptide, tensin. High tensin production per cell was detected in liquid media with glucose, mannitol or glutamate as growth substrate while fructose, sucrose and asparagine supported low production. Tensin production was nearly constant in media with different initial C levels, while low initial N contents reduced production. When applied to sugar beet seeds, strain 96.578 produced tensin during seed germination. When challenged with strain 96.578 or purified tensin, Rhizoctonia solani reduced radial mycelium extension but increased branching and rosette formation. CONCLUSION: The antagonistic activity of strain 96.578 towards Rhizoctonia solani was caused by tensin. SIGNIFICANCE AND IMPACT OF THE STUDY: When coated onto sugar beet seeds, tensin production by strain 96.578 could be of significant importance for inhibition of mycelial growth and seed infection by Rhizoctonia solani.

Anti-Bacterial Agents↗
PubMed2000

Pseudomonas frederiksbergensis sp. nov., isolated from soil at a coal gasification site.

Phenotypic and genotypic characterization indicated that a group of 29 closely related phenanthrene-degrading bacteria from a coal gasification site in Frederiksberg, Copenhagen, Denmark, belonged to the genus Pseudomonas. The strains were isolated at two sampling occasions 2 years apart. The isolates were phenotypically different from any known species of the genus Pseudomonas and were therefore subject to further identification. Colonies were smooth and pale yellowish and did not produce pigments fluorescent in UV light when grown on King's B agar. Cells were rod-shaped, approximately 0.5-0.8 x 1.5-3.0 microm, and grew at 4 and 30 degrees C, but not 37 degrees C. The bacteria were oxidase- and catalase-positive, accumulated poly-beta-hydroxybutyrate and denitrified, but did not utilize D-xylose. The mean G+C content was 59.6 mol%. Phenotypic data and 16S rDNA sequence data information for Pseudomonas amygdali and Pseudomonas corrugata, and 16S rDNA sequence data for Pseudomonas chlororaphis and Pseudomonas syringae showed close relationships to these strains. However, DNA-DNA hybridization data showed that the isolates belong to a new species, for which the name Pseudomonas frederiksbergensis sp. nov. is proposed. The type strain is JAJ28T (DSM 13022T).

Bacterial Typing Techniques↗
PubMed1999

Chitinolytic activity of Pseudomonas fluorescens isolates from barley and sugar beet rhizosphere.

Twelve isolates of Pseudomonas fluorescens, isolated from barley and sugar beet rhizosphere as antagonists towards the plant pathogenic microfungi Rhizoctonia solani and Pythium ultimum, showed chitinolytic activity in batch cultures when grown in media without exogenous chitin. Enzyme tests in cultures demonstrated a complete array of chitinolytic enzymes. Endochitinase and chitobiosidase activities seemed to be tightly coupled in the isolates, while there was no relationship to N-acetyl-glucosaminidase activity. Endochitinase activity, showing hydrolysis of chitin polymers, was found to be extracellular in all isolates, although the most active isolates also retained a cell-bound fraction. Isoelectric focusing gel electrophoresis of supernatants containing extracellular enzyme activity showed that all isolates produced one native endochitinase in logarithmic phase. This enzyme was subsequently modified into several isozymes by extracellular processing as the cultures aged in stationary phase. The 12 isolates could be grouped into seven isozymic patterns. Detailed studies of three selected isolates showed that extracellular release of endochitinase activity also took place in stationary phase. The results, however, indicated that in stationary phase regulation of both the overall production of native enzyme and the subsequent formation of isozymes were different among the P. fluorescens isolates.

Journal Article↗
PubMed1999

Viscosinamide, a new cyclic depsipeptide with surfactant and antifungal properties produced by Pseudomonas fluorescens DR54.

Pseudomonas fluorescens DR54 showed antagonistic properties against plant pathogenic Pythium ultimum and Rhizoctonia solani both in vitro and in planta. Antifungal activity was extractable from spent growth media, and fractionation by semi-preparative HPLC resulted in isolation of an active compound, which was identified as a new bacterial cyclic lipodepsipeptide, viscosinamide, using 1D and 2D 1H-, 13C-NMR and mass spectrometry. The new antibiotic has biosurfactant properties but differs from the known biosurfactant, viscosin, by containing glutamine rather than glutamate at the amino acid position 2 (AA2). No viscosin production was observed, however, when Ps. fluorescens DR54 was cultured in media enriched with glutamate. In vitro tests showed that purified viscosinamide also reduced fungal growth and aerial mycelium development of both P. ultimum and R. solani. Viscosinamide production by Ps. fluorescens DR54 was tightly coupled to cell proliferation in the batch cultures, as the viscosinamide produced per cell mass unit approached a constant value. In batch cultures with variable initial C, N or P nutrient levels, there were no indications of elevated viscosinamide production during starvation or maintenance of the cultures in stationary phase. Analysis of cellular fractions and spent growth media showed that a major fraction of the viscosinamide produced remained bound to the cell membrane of Ps. fluorescens DR54. The isolation, determination of structure and production characteristics of the new compound with both biosurfactant and antibiotic properties have promising perspectives for the application of Ps. fluorescens DR54 in biological control.

Antifungal Agents↗
PubMed1999

Oxygen-sensing reporter strain of Pseudomonas fluorescens for monitoring the distribution of low-oxygen habitats in soil.

The root-colonizing bacterium Pseudomonas fluorescens CHA0 was used to construct an oxygen-responsive biosensor. An anaerobically inducible promoter of Pseudomonas aeruginosa, which depends on the FNR (fumarate and nitrate reductase regulation)-like transcriptional regulator ANR (anaerobic regulation of arginine deiminase and nitrate reductase pathways), was fused to the structural lacZ gene of Escherichia coli. By inserting the reporter fusion into the chromosomal attTn7 site of P. fluorescens CHA0 by using a mini-Tn7 transposon, the reporter strain, CHA900, was obtained. Grown in glutamate-yeast extract medium in an oxystat at defined oxygen levels, the biosensor CHA900 responded to a decrease in oxygen concentration from 210 x 10(2) Pa to 2 x 10(2) Pa of O(2) by a nearly 100-fold increase in beta-galactosidase activity. Half-maximal induction of the reporter occurred at about 5 x 10(2) Pa. This dose response closely resembles that found for E. coli promoters which are activated by the FNR protein. In a carbon-free buffer or in bulk soil, the biosensor CHA900 still responded to a decrease in oxygen concentration, although here induction was about 10 times lower and the low oxygen response was gradually lost within 3 days. Introduced into a barley-soil microcosm, the biosensor could report decreasing oxygen concentrations in the rhizosphere for a 6-day period. When the water content in the microcosm was raised from 60% to 85% of field capacity, expression of the reporter gene was elevated about twofold above a basal level after 2 days of incubation, suggesting that a water content of 85% caused mild anoxia. Increased compaction of the soil was shown to have a faster and more dramatic effect on the expression of the oxygen reporter than soil water content alone, indicating that factors other than the water-filled pore space influenced the oxygen status of the soil. These experiments illustrate the utility of the biosensor for detecting low oxygen concentrations in the rhizosphere and other soil habitats.

Bacterial Proteins↗
PubMed1998

Gene transfer to Schwann cells after peripheral nerve injury: a delivery system for therapeutic agents.

We transferred a reporter gene to Schwann cells to test whether they might serve as an endoneurial delivery system for therapeutic proteins. A replication-defective adenoviral vector carrying the gene for beta-galactosidase (lacZ) was injected into the distal segment of intact or crushed sciatic nerves of adult rats, and the expression of lacZ was histochemically assessed. Less than 1% of the Schwann cells became reactive in intact nerves, but up to 18% of the proliferating Schwann cells of injured nerves expressed lacZ. Gene expression decayed with time but might persist for up to 2 months. It was enhanced by immunosuppression: daily cyclosporin A injections reduced both proliferation of Schwann cells and lymphocytic infiltration of the nerve, whereas tolerance induced by a single intrathymic injection of the vector 4 days after birth abolished the inflammatory response but not the proliferation of Schwann cells. The vector itself did not impede axonal regeneration. The results indicate that adenoviral gene transfer to Schwann cells in injured nerves is possible and suggest that induced production of neurotrophic factor may represent a therapeutic supplement to surgical nerve repair.

Animals↗