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Differences in Membrane Fluidity and Fatty Acid Composition between Phenotypic Variants of Streptococcus pneumoniae. Barak Aricha, 2004.Phase variation in the colonial opacity of Streptococcus pneumoniae has been implicated as a factor in the pathogenesis of pneumococcal disease . This study examined the relationship between membrane characteristics and colony morphology in a few selected opaque-transparent couples of S . pneumoniae strains carrying different capsular types . Membrane fluidity was determined on the basis of intermolecular excimerization of pyrene and fluorescence polarization of 1,6-diphenyl 1,3,5-hexatriene (DPH) . A significant decrease, 16 to 26% (P 
0.05), in the excimerization rate constant of the opaque variants
compared with that of the transparent variants was observed,
indicating higher microviscosity of the membrane of bacterial cells
in the opaque variants . Liposomes prepared from phospholipids of the
opaque phenotype showed an even greater decrease, 27 to 38% (P
0.05), in the pyrene excimerization rate constant compared with that
of liposomes prepared from phospholipids of bacteria with the
transparent phenotype . These findings agree with the results obtained
with DPH fluorescence anisotropy, which showed a 9 to 21% increase (P
0.001) in the opaque variants compared with the transparent variants .
Membrane fatty acid composition, determined by gas chromatography,
revealed that the two variants carry the same types of fatty acids
but in different proportions . The trend of modification points to the
presence of a lower degree of unsaturated fatty acids in the
opaque variants compared with their transparent counterparts . The
data presented here show a distinct correlation between phase
variation and membrane fluidity in S . pneumoniae . The changes
in membrane fluidity most probably stem from the observed differences
in fatty acid composition .
Oxidative-Stress Resistance Mutants of Helicobacter pylori. Adriana A. Olczak, 2002.Within a large family of peroxidases, one member that catalyzes the reduction of organic peroxides to alcohols is known as alkyl hydroperoxide reductase, or AhpC . Gene disruption mutations in the gene encoding AhpC of Helicobacter pylori (ahpC) were generated by screening transformants under low-oxygen conditions . Two classes of mutants were obtained . Both types lack AhpC protein, but the major class (type I) isolated was found to synthesize increased levels (five times more than the wild type) of another proposed antioxidant protein, an iron-binding, neutrophil-activating protein (NapA) . The other class of mutants, the minor class (type II), produced wild-type levels of NapA . The two types of AhpC mutants differed in their frequencies of spontaneous mutation to rifampin resistance and in their sensitivities to oxidative-stress chemicals, with the type I mutants exhibiting less sensitivity to organic hydroperoxides as well as having a lower mutation frequency . The napA promoter regions of the two types of AhpC mutants were identical, and primer extension analysis revealed their transcription start site to be the same as for the wild type . Gene disruption mutations were obtained in napA alone, and a double mutant strain (ahpC napA) was also created . All four of the oxidative-stress resistance mutants could be distinguished from the wild type in oxygen sensitivity or in some other oxidative-stress resistance phenotype (i.e., in sensitivity to stress-related chemicals and spontaneous mutation frequency) . For example, growth of the NapA mutant was more sensitive to oxygen than that of the wild-type strain and both of the AhpC-type mutants were highly sensitive to paraquat and to cumene hydroperoxide . Of the four types of mutants, the double mutant was the most sensitive to growth inhibition by oxygen and by organic peroxides and it had the highest spontaneous mutation frequency . Notably, two-dimensional gel electrophoresis combined with protein sequence analysis identified another possible oxidative-stress resistance protein (HP0630) that was up-regulated in the double mutant . However, the transcription start site of the HP0630 gene was the same for the double mutant as for the wild type . It appears that H . pylori can readily modulate the expression of other resistance factors as a compensatory response to loss of a major oxidative-stress resistance component . Recruitment of MinC, an Inhibitor of Z-Ring Formation, to the Membrane in Escherichia coli: Role of MinD and MinE. Zonglin Hu, 2003.In Escherichia coli, the min system prevents division away from midcell through topological regulation of MinC, an inhibitor of Z-ring formation . The topological regulation involves oscillation of MinC between the poles of the cell under the direction of the MinDE oscillator . Since the mechanism of MinC involvement in the oscillation is unknown, we investigated the interaction of MinC with the other Min proteins . We observed that MinD dimerized in the presence of ATP and interacted with MinC . In the presence of a phospholipid bilayer, MinD bound to the bilayer and recruited MinC in an ATP-dependent manner . Addition of MinE to the MinCD-bilayer complex resulted in release of both MinC and MinD . The release of MinC did not require ATP hydrolysis, indicating that MinE could displace MinC from the MinD-bilayer complex . In contrast, MinC was unable to displace MinE bound to the MinD-bilayer complex . These results suggest that MinE induces a conformational change in MinD bound to the bilayer that results in the release of MinC . Also, it is argued that binding of MinD to the membrane activates MinC . PhaQ, a New Class of Poly-ß-Hydroxybutyrate (PHB)-Responsive Repressor, Regulates phaQ and phaP (Phasin) Expression in Bacillus megaterium through Interaction with PHB. Tian-Ren Lee, 2004.Bacillus megaterium can produce poly-ß-hydroxybutyrate (PHB) as carbon and energy storage materials . We now report that the phaQ gene, which is located upstream of the phasin-encoding phaP gene, codes for a new class of transcriptional regulator that negatively controls expression of both phaQ and phaP . A PhaQ binding site that plays a role in this control has been identified by gel mobility shift assays and DNase I footprinting analysis . We have also provided evidence that PhaQ could sense the presence of PHB in vivo and that artificial PHB granules could inhibit the formation of PhaQ-DNA complex in vitro by binding to PhaQ directly . These suggest that PhaQ is a PHB-responsive repressor .
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