|
|
|
|
|
|
An SOS Response Induced by High Pressure in Escherichia coli. Abram Aertsen, 2004.Although pressure is an important environmental parameter in microbial niches such as the deep sea and is furthermore usedin food preservation to inactivate microorganisms, the fundamental understanding of its effects on bacteria remains fragmentary.Our group recently initiated differential fluorescence induction screening to search for pressure-induced Escherichia coli promoters and has already reported induction of the heat shock regulon. Here the screening was continued, and we report for the firsttime that pressure induces a bona fide SOS response in E . coli, characterized by the RecA and LexA-dependent expression of uvrA, recA, and sulA . Moreover, it was shown that pressure is capableof triggering lambda prophage induction in E . coli lysogens.The remnant lambdoid e14 element, however, could not be inducedby pressure, as opposed to UV irradiation, indicating subtle differences between the pressure-induced and the classical SOS response . Furthermore, the pressure-induced SOS response seemsnot to be initiated by DNA damage, since  recA
and lexA1 [Ind–]mutants, which are intrinsically
hypersensitive to DNA damage,were not sensitized or were only very
slightly sensitized forpressure-mediated killing and since pressure
treatment was notfound to be mutagenic . In light of these findings,
the currentknowledge of pressure-mediated effects on bacteria is
discussed.
Mutational Analysis and Biochemical Characterization of the Burkholderia thailandensis DW503 Quorum-Sensing Network. Ricky L. Ulrich, 2004.Numerous gram-negative bacteria communicate and regulate gene expression through a cell density-responsive mechanism termed quorum sensing (QS), which involves the synthesis and perception of diffusible N-acyl-homoserine lactones (AHL) . In this study we genetically and physiologically characterized the Burkholderia thailandensis DW503 QS network . In silico analysis of the B . thailandensis genome revealed the presence of at least three AHL synthases (AHS) and five transcriptional regulators belonging to the LuxIR family of proteins . Mass spectrometry demonstrated that wild-type B . thailandensis synthesizes N-hexanoyl-homoserine lactone (C6-HSL), N-octanoyl-homoserine lactone (C8-HSL), and N-decanoyl-homoserine lactone (C10-HSL) . Mutation of the btaI1 (luxI) AHS gene prevented accumulation of C8-HSL in culture supernatants, enhanced beta-hemolysis of sheep erythrocytes, increased lipase production, and altered colony morphology on swarming and twitching motility plates . Disruption of the btaI3 (luxI) AHS prevented biosynthesis of C6-HSL and increased lipase production and beta-hemolysis, whereas mutagenesis of the btaI2 (luxI) allele eliminated C10-HSL accumulation and reduced lipase production . Complementation of the btaI1 and btaI3 mutants fully restored the synthesis of C8-HSL and C6-HSL to parental levels . In contrast, mutagenesis of the btaR1, btaR3, btaR4, and btaR5 (luxR) transcriptional regulators had no effect on AHL accumulation, enhanced lipase production, and resulted in extensive beta-hemolysis on sheep blood agar plates . Furthermore, interruption of the btaI1, btaR1, and btaR3 genes altered colony morphology on twitching and swarming motility plates and induced pigmentation . Additionally, phenotypic microarray analysis indicated that QS in B . thailandensis both positively and negatively affects the metabolism of numerous substrates, including citric acid, formic acid, glucose 6-phosphate, capric acid,  -hydroxybutyric
acid, and D-arabinose . These results
demonstrate that mutagenesis of the B . thailandensis QS system
affects various cellular processes, including lipase production,
swarming and twitching motility, beta-hemolysis of sheep erythrocytes,
and carbon metabolism and/or transport .
vanE Gene Cluster of Vancomycin-Resistant Enterococcus faecalis BM4405. Lorena Abadía Patiño, 2002. Glutathione Protects Lactococcus lactis against Oxidative Stress. Yin Li, 2003.Glutathione was found in several dairy Lactococcus lactis strains grown in M17 medium . None of these strains was able to synthesize glutathione . In chemically defined medium, L . lactis subsp . cremoris strain SK11 was able to accumulate up to  60 mM glutathione when this compound was added to the medium . Stationary-phase cells of strain SK11 grown in chemically defined medium supplemented with glutathione showed significantly increased resistance (up to fivefold increased resistance) to treatment with H2O2 compared to the resistance of cells without intracellular glutathione . The resistance to H2O2 treatment was found to be dependent on the accumulation of glutathione in 16 strains of L . lactis tested . We propose that by taking up glutathione, L . lactis might activate a glutathione-glutathione peroxidase-glutathione reductase system in stationary-phase cells, which catalyzes the reduction of H2O2 . Glutathione reductase, which reduces oxidized glutathione, was detectable in most strains of L . lactis, but the activities of different strains were very variable . In general, the glutathione reductase activities of L . lactis subsp . lactis are higher than those of L . lactis subsp . cremoris, and the activities were much higher when strains were grown aerobically . In addition, glutathione peroxidase is detectable in strain SK11, and the level was fivefold greater when the organism was grown aerobically than when the organism was grown anaerobically . Therefore, the presence of glutathione in L . lactis could result in greater stability under storage conditions and quicker growth upon inoculation, two important attributes of successful starter cultures .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
