|
|
|
|
|
|
Expression of Vibrio vulnificus Capsular Polysaccharide Inhibits Biofilm Formation. Lavin A. Joseph, 2004.Vibrio vulnificus is a human pathogen that produces lethal septicemia in susceptible persons, and the primary virulence factor for this organism is capsular polysaccharide (CPS) . The role of the capsule in V . vulnificus biofilms was examined under a variety of conditions, by using either defined CPS mutants or spontaneous CPS expression phase variants derived from multiple strains . CPS expression was shown to inhibit attachment and biofilm formation, which contrasted with other studies describing polysaccharides as integral to biofilms in related species . Influence of Complex Nutrient Source on Growth of and Curvacin A Production by Sausage Isolate Lactobacillus curvatus LTH 1174. Jurgen Verluyten, 2004.Lactobacillus curvatus LTH 1174, a fermented sausage isolate, produces the antilisterial bacteriocin curvacin A . Its biokinetics of cell growth and bacteriocin production as a function of various concentrations of a complex nutrient source were investigated in vitro during laboratory fermentations with modified MRS medium . A modification of the nutrient depletion model (Leroy and De Vuyst, Appl . Environ, Microbiol . 67:4470-4473, 2001) was used to fit the data describing growth and bacteriocin production . Both cell growth and bacteriocin activity were influenced by changes in the complex nutrient source concentration . Standard MRS medium clearly limited the growth of L . curvatus LTH 1174 . Higher nutrient concentrations, up to a certain degree, led to improved growth, a higher attainable biomass concentration, and a higher bacteriocin activity in the supernatant . A lower concentration of complex nutrient source caused severe growth inhibition, leading to a lower biomass concentration but a much higher specific bacteriocin production . When examining the separate components of the complex nutrient source, a stimulating effect of bacteriological peptone on growth was found without an adverse effect on bacteriocin production, resulting in increased curvacin A activity . Furthermore, specific depletion of the amino acids tyrosine, serine, and asparagine/aspartic acid was observed for this strain . Recombination-Promoting Activity of the Bacteriophage  Rap Protein in Escherichia coli K-12.Anthony R. Poteete, 2002.The rap gene of bacteriophage was placed in the chromosome of an Escherichia coli K-12 strain in which the recBCD gene cluster had previously been replaced by the
red genes and in which the recG gene had been deleted . Recombination between linear double-stranded DNA molecules and the chromosome was tested in variants of the recG red+ rap+ strain bearing mutations in genes known to affect recombination in other cellular pathways . The linear DNA was a 4-kb fragment containing the cat gene, with flanking lac sequences, released from an infecting phage chromosome by restriction enzyme cleavage in the cell . Replacement of wild-type lacZ with lacZ::cat was monitored by measuring the production of Lac-deficient chloramphenicol-resistant bacterial progeny . The results of these experiments indicated that the
rap gene could functionally substitute for the E . coli ruvC gene in Red-mediated recombination .
act Operon Control of Developmental Gene Expression in Myxococcus xanthus. Thomas M. A. Gronewold, 2002.Cell-bound C-signal guides the building of a fruiting body and triggers the differentiation of myxospores . Earlier work has shown that transcription of the csgA gene, which encodes the C-signal, is directed by four genes of the act operon . To see how expression of the genes encoding components of the aggregation and sporulation processes depends on C-signaling, mutants with loss-of-function mutations in each of the act genes were investigated . These mutations were found to have no effect on genes that are normally expressed up to 3 h into development and are C-signal independent . Neither the time of first expression nor the rate of expression increase was changed in actA, actB, actC, or actD mutant strains . Also, there was no effect on A-signal production, which normally starts before 3 h . By contrast, the null act mutants have striking defects in C-signal production . These mutations changed the expression of four gene reporters that are related to aggregation and sporulation and are expressed at 6 h or later in development . The actA and actB null mutations substantially decreased the expression of all these reporters . The other act null mutations caused either premature expression to wild-type levels (actC) or delayed expression (actD), which ultimately rose to wild-type levels . The pattern of effects on these reporters shows how the C-signal differentially regulates the steps that together build a fruiting body and differentiate spores within it . Susceptibility and Adaptive Response to Bile Salts in Propionibacterium freudenreichii: Physiological and Proteomic Analysis. Pauline Leverrier, 2003.Tolerance to digestive stresses is one of the main factors limiting the use of microorganisms as live probiotic agents . Susceptibility to bile salts and tolerance acquisition in the probiotic strain Propionibacterium freudenreichii SI41 were characterized . We showed that pretreatment with a moderate concentration of bile salts (0.2 g/liter) greatly increased its survival during a subsequent lethal challenge (1.0 g/liter, 60 s) . Bile salts challenge led to drastic morphological changes, consistent with intracellular material leakage, for nonadapted cells but not for preexposed ones . Moreover, the physiological state of the cells during lethal treatment played an important role in the response to bile salts, as stationary-phase bacteria appeared much less sensitive than exponentially growing cells . Either thermal or detergent pretreatment conferred significantly increased protection toward bile salts challenge . In contrast, some other heterologous pretreatments (hypothermic and hyperosmotic) had no effect on tolerance to bile salts, while acid pretreatment even might have sensitized the cells . Two-dimensional electrophoresis experiments revealed that at least 24 proteins were induced during bile salts adaptation . Identification of these polypeptides suggested that the bile salts stress response involves signal sensing and transduction, a general stress response (also triggered by thermal denaturation, oxidative toxicity, and DNA damage), and an alternative sigma factor . Taken together, our results provide new insights into the tolerance of P . freudenreichii to bile salts, which must be taken into consideration for the use of probiotic strains and the improvement of technological processes .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
