|
|
|
|
|
|
Purification and Characterization of Recombinant Staphylococcus haemolyticus DNA Gyrase and Topoisomerase IV Expressed in Escherichia coli. Joel C. Bronstein, 2004.The subunits of DNA gyrase and topoisomerase IV from Staphylococcus haemolyticus were expressed in Escherichia coli, purified to homogeneity, and used to reconstitute active enzymes that were sensitive to known topoisomerase inhibitors . This represents the first description of a method for isolating type II topoisomerases of a coagulase-negative staphylococcal species . Spatial Distribution of Bacterial Communities and Phenanthrene Degradation in the Rhizosphere of Lolium perenne L.. S. C. Corgié, 2004.Rhizodegradation of organic pollutants, such as polycyclic aromatic hydrocarbons, is based on the effect of root-produced compounds, known as exudates . These exudates constitute an important and constant carbon source that selects microbial populations in the plant rhizosphere, modifying global as well as specific microbial activities . We conducted an experiment in two-compartment devices to show the selection of bacterial communities by root exudates and phenanthrene as a function of distance to roots . Using direct DNA extraction, PCR amplification, and thermal gradient gel electrophoresis screening, bacterial population profiles were analyzed in parallel to bacterial counts and quantification of phenanthrene biodegradation in three layers (0 to 3, 3 to 6, and 6 to 9 mm from root mat) of unplanted-polluted (phenanthrene), planted-polluted, and planted-unpolluted treatments . Bacterial community differed as a function of the distance to roots, in both the presence and the absence of phenanthrene . In the planted and polluted treatment, biodegradation rates showed a strong gradient with higher values near the roots . In the nonplanted treatment, bacterial communities were comparable in the three layers and phenanthrene biodegradation was high . Surprisingly, no biodegradation was detected in the section of planted polluted treatment farthest from the roots, where the bacterial community structure was similar to those of the nonplanted treatment . We conclude that root exudates and phenanthrene induce modifications of bacterial communities in polluted environments and spatially modify the activity of degrading bacteria . Pseudomonas aeruginosa Virulence Analyzed in a Dictyostelium discoideum Host System. Pierre Cosson, 2002.Pseudomonas aeruginosa is an important opportunistic pathogen that produces a variety of cell-associated and secreted virulence factors . P . aeruginosa infections are difficult to treat effectively because of the rapid emergence of antibiotic-resistant strains . In this study, we analyzed whether the amoeba Dictyostelium discoideum can be used as a simple model system to analyze the virulence of P . aeruginosa strains . The virulent wild-type strain PAO1 was shown to inhibit growth of D . discoideum . Isogenic mutants deficient in the las quorum-sensing system were almost as inhibitory as the wild type, while rhl quorum-sensing mutants permitted growth of Dictyostelium cells . Therefore, in this model system, factors controlled by the rhl quorum-sensing system were found to play a central role . Among these, rhamnolipids secreted by the wild-type strain PAO1 could induce fast lysis of D . discoideum cells . By using this simple model system, we predicted that certain antibiotic-resistant mutants of P . aeruginosa should show reduced virulence . This result was confirmed in a rat model of acute pneumonia . Thus, D . discoideum could be used as a simple nonmammalian host system to assess pathogenicity of P . aeruginosa . Aerobic Anoxygenic Photosynthesis in Roseobacter Clade Bacteria from Diverse Marine Habitats. Martin Allgaier, 2003.The marine Roseobacter clade comprises several genera of marine bacteria related to the uncultured SAR83 cluster, the second most abundant marine picoplankton lineage . Cultivated representatives of this clade are physiologically heterogeneous, and only some have the capability for aerobic anoxygenic photosynthesis, a process of potentially great ecological importance in the world's oceans . In an attempt to correlate phylogeny with ecology, we investigated the diversity of Roseobacter clade strains from various marine habitats (water samples, biofilms, laminariae, diatoms, and dinoflagellate cultures) by using the 16S rRNA gene as a phylogenetic marker gene . The potential for aerobic anoxygenic photosynthesis was determined on the genetic level by PCR amplification and sequencing of the pufLM genes of the bacterial photosynthesis reaction center and on the physiological level by detection of bacteriochlorophyll (Bchl) a. A collection of ca . 1,000 marine isolates was screened for members of the marine Roseobacter clade by 16S rRNA gene-directed multiplex PCR and sequencing . The 42 Roseobacter clade isolates found tended to form habitat-specific subclusters . The pufLM genes were detected in two groups of strains from dinoflagellate cultures but in none of the other Roseobacter clade isolates . Strains within the first group (the DFL-12 cluster) also synthesized Bchl a. Strains within the second group (the DFL-35 cluster) formed a new species of Roseovarius and did not produce Bchl a under the conditions investigated here, thus demonstrating the importance of genetic methods for screening of cultivation-dependent metabolic traits . The pufL genes of the dinoflagellate isolates were phylogenetically closely related to pufL genes from Betaproteobacteria, confirming similar previous observations which have been interpreted as indications of gene transfer events .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
