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Volume 146,
Issue 11,
2000
Volume 146, Issue 11, 2000
- Pathogenicity And Medical Microbiology
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The plcR regulon is involved in the opportunistic properties of Bacillus thuringiensis and Bacillus cereus in mice and insects
Bacillus thuringiensis has been widely used for 40 years as a safe biopesticide for controlling agricultural pests and mosquitoes because it produces insecticidal crystal proteins. However, spores have also been shown to contribute to overall entomopathogenicity. Here, the opportunistic properties of acrystalliferous B. thuringiensis Cry− and Bacillus cereus strains were investigated in an insect species, Galleria mellonella, and in a mammal, BALB/c mice. In both animal models, the pathogenicity of the two bacterial species was similar. Mutant strains were constructed in which the plcR gene, encoding a pleiotropic regulator of extracellular factors, was disrupted. In larvae, co-ingestion of 106 spores of the parental strain with a sublethal concentration of Cry1C toxin caused 70% mortality whereas only 7% mortality was recorded if spores of the ΔplcR mutant strain were used. In mice, nasal instillation of 108 spores of the parental strain caused 100% mortality whereas instillation with the same number of ΔplcR strain spores caused much lower or no mortality. Similar effects were obtained if vegetative cells were used instead of spores. The cause of death is unknown and is unlikely to be due to actual growth of the bacteria in mice. The lesions caused by B. thuringiensis supernatant in infected mice suggested that haemolytic toxins were involved. The cytolytic properties of strains of B. thuringiensis and B. cereus, using sheep, horse and human erythrocytes and G. mellonella haemocytes, were therefore investigated. The level of cytolytic activity is highly reduced in ΔplcR strains. Together, the results indicate that the pathogenicity of B. thuringiensis strain 407 and B. cereus strain ATCC 14579 is controlled by PlcR.
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- Physiology And Growth
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Involvement of the rml locus in core oligosaccharide and O polysaccharide assembly in Pseudomonas aeruginosa
More Lessl-Rhamnose (l-Rha) is a component of the lipopolysaccharide (LPS) core, several O antigen polysaccharides, and the cell surface surfactant rhamnolipid of Pseudomonas aeruginosa. In this study, four contiguous genes (rmlBDAC) responsible for the synthesis of dTDP-l-Rha in P. aeruginosa have been cloned and characterized. Non-polar chromosomal rmlC mutants were generated in P. aeruginosa strains PAO1 (serotype O5) and PAK (serotype O6) and LPS extracted from the mutants was analysed by SDS-PAGE and Western immunoblotting. rmlC mutants of both serotype O5 and serotype O6 synthesized a truncated core region which was unable to act as an attachment point for either A-band or B-band O antigen. A rmd rmlC PAO1 double mutant (deficient in biosynthesis of both d-Rha and l-Rha) was constructed to facilitate structural analysis of the mutant core region. This strain has an incomplete core oligosaccharide region and does not produce A-band O antigen. These results provide the genetic and structural evidence that l-Rha is the receptor on the P. aeruginosa LPS core for the attachment of O polysaccharides. This is the first report of a genetically defined mutation that affects the synthesis of a single sugar in the core oligosaccharide region of P. aeruginosa LPS, and provides further insight into the mechanisms of LPS biosynthesis and assembly in this bacterium.
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A novel thermostable multidomain 1,4-β-xylanase from ‘Caldibacillus cellulovorans’ and effect of its xylan-binding domain on enzyme activity
More LessThe GenBank accession number for the sequence reported in this paper is AF200304.
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A periplasmic, α-type carbonic anhydrase from Rhodopseudomonas palustris is essential for bicarbonate uptake
More LessIntact cells of the purple non-sulfur bacterium Rhodopseudomonas palustris growing anaerobically, but not aerobically, contain carbonic anhydrase (CA) activity. The native enzyme was purified >2000-fold to apparent homogeneity and found to be a dimer with an estimated molecular mass of 54 kDa and a subunit molecular mass of 27 kDa. The CA gene (acaP) was cloned and its sequence revealed that it was homologous to α-type CAs. The upstream region of acaP was fused to the lacZ gene and β-galactosidase activity was measured under different growth conditions. Acetazolamide inhibited purified CA with an IC50 in the range of 10−8 M, and in the culture media concentrations as low as 30 μM inhibited phototrophic growth under anaerobic, light conditions when bicarbonate was used. An acaP::Kan r mutant strain was constructed by insertion of a kanamycin-resistance cassette and showed a growth pattern similar to wild-type cells grown in the presence of CA inhibitor. CO2 gas supplied as an inorganic carbon source reversed the effect of mutation or acetazolamide. CA activity measurements, fusion and Western blot experiments confirmed that CA is expressed under different anaerobic conditions independently of bicarbonate or CO2 and that there is no expression under aerobic conditions.
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Growth inhibition of Escherichia coli by dichloromethane in cells expressing dichloromethane dehalogenase/glutathione S-transferase
More LessDichloromethane (DCM) dehalogenase converts DCM to formaldehyde via the formation of glutathione metabolites and generates 2 mol HCl per mol DCM metabolized. Growth of Escherichia coli expressing DCM dehalogenase was immediately and severely inhibited during conversion of 0·3 mM DCM. Intracellular pH (pHi) rapidly decreased and chloride ions were steadily released into the medium. Bacterial growth resumed after completion of DCM conversion and cell viability was unaffected. At 0·6 mM DCM there was no recovery from growth inhibition in liquid culture due to the build-up of inhibitory concentrations of formaldehyde. DCM turnover stimulated potassium efflux from cells, which was suppressed by glucose. The potassium efflux, therefore, did not contribute to growth inhibition. It was concluded that initial growth inhibition results from lowering of the cytoplasmic pH, but severity of growth inhibition was greater than expected for the change in pHi. Possible contributors to growth inhibition are discussed.
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Lipid composition and taxonomy of [Pseudomonas] echinoides: transfer to the genus Sphingomonas
More LessLipid components of [Pseudomonas] echinoides NCIMB 9420 have been studied as an aid to taxonomic relocation of the organism. Non-polar lipids include the carotenoid nostoxanthin and the ubiquinone Q-10. The major fatty acids are cis-vaccenic acid [18:1(11c)], hexadecanoic acid (16:0) and 2-hydroxy-tetradecanoic acid (2-OH-14:0), but 11-methyloctadec-11-enoic acid[11-Me-18:1(11)] is a significant minor component. The preponderant phospholipids are phosphatidylethanolamine and phosphatidylglycerol; minor lipids include bis(phosphatidyl)glycerol and an unidentified aminophospholipid. Several glycolipids are present, the major one being a glucuronosylceramide derived from sphinganine with amide-bound 2-OH-14:0. The lipid profile supports a proposal to reclassify the organism as Sphingomonas echinoides.
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High hopanoid/total lipids ratio in Frankia mycelia is not related to the nitrogen status
The GenBank/EMBL/DDBJ accession numbers for the sequences in this paper are AJ251388–91 and AJ251393–4.
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- Plant-Microbe Interactions
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The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation
More LessThe GenBank accession number for the sequence reported in this paper is AF155830.
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Phylogenetic diversity of rhizobial strains nodulating Robinia pseudoacacia L.
More LessThe EMBL accession numbers for the sequences reported in this paper are AJ271898–AJ271902 for the Mesorhizobium strains Rob6, Rob8 and Rob23 and the Rhizobium strains Rob18 and Rob20, respectively.
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- Systematics And Evolution
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Comparative sequence analyses reveal frequent occurrence of short segments containing an abnormally high number of non-random base variations in bacterial rRNA genes
More LessThe GenBank accession numbers for the 23S rRNA sequences determined in this study are AF192136–AF192150.
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