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The Bvg Virulence Control System Regulates Biofilm Formation in Bordetella bronchiseptica. Yasuhiko Irie, 2004.Bordetella species utilize the BvgAS (Bordetella virulence gene) two-component signal transduction system to sense the environment and regulate gene expression among at least three phases: a virulent Bvg+ phase, a nonvirulent Bvg– phase, and an intermediate Bvgi phase . Genes expressed in the Bvg+ phase encode known virulence factors, including adhesins such as filamentous hemagglutinin (FHA) and fimbriae, as well as toxins such as the bifunctional adenylate cyclase/hemolysin (ACY) . Previous studies showed that in the Bvgi phase, FHA and fimbriae continue to be expressed, but ACY expression is significantly downregulated . In this report, we determine that Bordetella bronchiseptica can form biofilms in vitro and that the generation of biofilm is maximal in the Bvgi phase . We show that FHA is required for maximal biofilm formation and that fimbriae may also contribute to this phenotype . However, expression of ACY inhibits biofilm formation, most likely via interactions with FHA . Therefore, the coordinated regulation of adhesins and ACY expression leads to maximal biofilm formation in the Bvgi phase in B . bronchiseptica . Increasing the Oxidative Stress Response Allows Escherichia coli To Overcome Inhibitory Effects of Condensed Tannins. Alexandra H. Smith, 2003.Tannins are plant-derived polyphenols with antimicrobial effects . The mechanism of tannin toxicity towards Escherichia coli was determined by using an extract from Acacia mearnsii (Black wattle) as a source of condensed tannins (proanthocyanidins) . E . coli growth was inhibited by tannins only when tannins were exposed to oxygen . Tannins auto-oxidize, and substantial hydrogen peroxide was generated when they were added to aerobic media . The addition of exogenous catalase permitted growth in tannin medium . E . coli mutants that lacked HPI, the major catalase, were especially sensitive to tannins, while oxyR mutants that constitutively overexpress antioxidant enzymes were resistant . A tannin-resistant mutant was isolated in which a promoter-region point mutation increased the level of HPI by 10-fold . Our results indicate that wattle condensed tannins are toxic to E . coli in aerobic medium primarily because they generate H2O2 . The oxidative stress response helps E . coli strains to overcome their inhibitory effect . A Novel Extracellular Multicopper Oxidase from Phanerochaete chrysosporium with Ferroxidase Activity. Luis F. Larrondo, 2003.Lignin degradation by the white rot basidiomycete Phanerochaete chrysosporium involves various extracellular oxidative enzymes, including lignin peroxidase, manganese peroxidase, and a peroxide-generating enzyme, glyoxal oxidase . Recent studies have suggested that laccases also may be produced by this fungus, but these conclusions have been controversial . We identified four sequences related to laccases and ferroxidases (Fet3) in a search of the publicly available P . chrysosporium database . One gene, designated mco1, has a typical eukaryotic secretion signal and is transcribed in defined media and in colonized wood . Structural analysis and multiple alignments identified residues common to laccase and Fet3 sequences . A recombinant MCO1 (rMCO1) protein expressed in Aspergillus nidulans had a molecular mass of 78 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the copper I-type center was confirmed by the UV-visible spectrum . rMCO1 oxidized various compounds, including 2,2'-azino(bis-3-ethylbenzthiazoline-6-sulfonate) (ABTS) and aromatic amines, although phenolic compounds were poor substrates . The best substrate was Fe2+, with a Km close to 2 µM . Collectively, these results suggest that the P . chrysosporium genome does not encode a typical laccase but rather encodes a unique extracellular multicopper oxidase with strong ferroxidase activity .
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