|
|
|
|
|
|
The Alternative Sigma Factor  B
of Bacillus cereus: Response to Stress and Role in Heat Adaptation.Willem van Schaik, 2004.A gene cluster encoding the alternative sigma factor B,
three predicted regulators of
B
(RsbV, RsbW, and RsbY), and one protein whose function is not known
(Orf4) was identified in the genome sequence of the food pathogen
Bacillus cereus ATCC 14579 . Western blotting with polyclonal
antibodies raised against
B
revealed that there was 20.1-fold activation of
B
after a heat shock from 30 to 42°C . Osmotic upshock and ethanol
exposure also upregulated
B,
albeit less than a heat shock . When the intracellular ATP
concentration was decreased by exposure to carbonyl cyanide m-chlorophenylhydrazone
(CCCP), only limited increases in
B
levels were observed, revealing that stress due to ATP depletion
is not an important factor in
B
activation in B . cereus . Analysis of transcription of the
sigB operon by Northern blotting and primer extension revealed
the presence of a
B-dependent
promoter upstream of the first open reading frame (rsbV) of
the sigB operon, indicating that transcription of sigB
is autoregulated . A second
B-dependent
promoter was identified upstream of the last open reading frame (orf4)
of the sigB operon . Production of virulence factors and the
nonhemolytic enterotoxin Nhe in a sigB null mutant was the
same as in the parent strain . However,
B
was found to play a role in the protective heat shock response of
B . cereus . The sigB null mutant was less protected against
the lethal temperature of 50°C by a preadaptation to 42°C than the
parent strain was, resulting in a more-than-100-fold-reduced survival
of the mutant after 40 min at 50°C .
Use of Aqueous Silver To Enhance Inactivation of Coliphage MS-2 by UV Disinfection. Michael A. Butkus, 2004.A synergistic effect between silver and UV radiation has been observed that can appreciably enhance the effectiveness of UV radiation for inactivation of viruses . At a fluence of ca . 40 mJ/cm2, the synergistic effect between silver and UV was observed at silver concentrations as low as 10 µg/liter (P < 0.0615) . At the same fluence, an MS-2 inactivation of ca . 3.5 logs (99.97%) was achieved at a silver concentration of 0.1 mg/liter, a significant improvement (P < 0.0001) over the ca . 1.8-log (98.42%) inactivation of MS-2 at ca . 40 mJ/cm2 in the absence of silver . Modified Chick-Watson kinetics were used to model the synergistic effect of silver and UV radiation . For an MS-2 inactivation of 4 logs (99.99%), the coefficient of dilution (n) was determined to be 0.31, which suggests that changes in fluence have a greater influence on inactivation than does a proportionate change in silver concentration . Genetic Screen Yields Mutations in Genes Encoding All Known Components of the Escherichia coli Signal Recognition Particle Pathway. Hongping Tian, 2002.We describe the further utilization of a genetic screen that identifies mutations defective in the assembly of proteins into the Escherichia coli cytoplasmic membrane . The screen yielded mutations in each of the known genes encoding components of the E . coli signal recognition particle pathway: ffh, ffs, and ftsY, which encode Ffh, 4.5S RNA, and FtsY, respectively . In addition, the screen yielded mutations in secM, which is involved in regulating levels of the SecA component of the bacterium’s protein export pathway . We used a sensitive assay involving biotinylation to show that all of the mutations caused defects in the membrane insertions of three topologically distinct membrane proteins, AcrB, MalF, and FtsQ . Among the mutations that resulted in membrane protein insertion defects, only the secM mutations also showed defects in the translocation of proteins into the E . coli periplasm . Genetic evidence suggests that the S382T alteration of Ffh affects the interaction between Ffh and 4.5S RNA . Control of Inducer Accumulation Plays a Key Role in Succinate-Mediated Catabolite Repression in Sinorhizobium meliloti. Ryan M. Bringhurst, 2002.The symbiotic, nitrogen-fixing bacterium Sinorhizobium meliloti favors succinate and related dicarboxylic acids as carbon sources . As a preferred carbon source, succinate can exert catabolite repression upon genes needed for the utilization of many secondary carbon sources, including the  -galactosides raffinose and stachyose . We isolated lacR mutants in a genetic screen designed to find S . meliloti mutants that had abnormal succinate-mediated catabolite repression of the melA-agp genes, which are required for the utilization of raffinose and other
-galactosides . The loss of catabolite repression in lacR mutants was seen in cells grown in minimal medium containing succinate and raffinose and grown in succinate and lactose . For succinate and lactose, the loss of catabolite repression could be attributed to the constitutive expression of ß-galactoside utilization genes in lacR mutants . However, the inactivation of lacR did not cause the constitutive expression of
-galactoside utilization genes but caused the aberrant expression of these genes only when succinate was present . To explain the loss of diauxie in succinate and raffinose, we propose a model in which lacR mutants overproduce ß-galactoside transporters, thereby overwhelming the inducer exclusion mechanisms of succinate-mediated catabolite repression . Thus, some raffinose could be transported by the overproduced ß-galactoside transporters and cause the induction of
-galactoside utilization genes in the presence of both succinate and raffinose . This model is supported by the restoration of diauxie in a lacF lacR double mutant (lacF encodes a ß-galactoside transport protein) grown in medium containing succinate and raffinose . Biochemical support for the idea that succinate-mediated repression operates by preventing inducer accumulation also comes from uptake assays, which showed that cells grown in raffinose and exposed to succinate have a decreased rate of raffinose transport compared to control cells not exposed to succinate .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
