The effect of composition of the core region of Escherichia coli K-12 lipopolysaccharides on the surface properties of cells

Microbiology (Impact Factor: 0.65). 05/2008; 77(3):293-297. DOI: 10.1134/S0026261708030077

ABSTRACT The pH dependences of electrokinetic potentials (EKP) of the cells of two Escherichia coli K-12 strains (D21 and JM 103) with known lipopolysaccharide (LPS) core composition have been determined by the method of
microelectrophoresis. At pH 4.6–5.2, the negative surface charge of the cells with Re core LPS was reliably higher. It was
shown that the interaction of bacteria with lysozyme results in a decrease of optical density of suspensions due to higher
sensitivity of the cells with complete LPS core to hypotonic shock. LPS release from bacterial cell wall depended also on
bacterial LPS core composition and increased with LPS core extension. Electrokinetic measurements and the study of the interaction
of cells with lysozyme suggest that higher negative surface charge of E. coli JM 103 cells (Re type LPS) is associated with higher quantity and density of LPS packing in the cell wall as compared with
the cells of E. coli D21 (Ra type LPS).

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    ABSTRACT: The electrophoretic mobility (EPM) of a variety of Gram-negative and Gram-positive bacteria was measured with a Penkem S3000 analyser. Under standard growth conditions and neutral pH all cells displayed a negative EPM. The polysaccharide capsules of Escherichia coli strains K1, K5, K29 and K30 generated the highest EPM; to a lesser and varying degree O-antigens with charged groups and core lipopolysaccharides also contribute to the net EPM. Very little negative EPM was measured in suspension cultures of the gliding bacterium Cytophaga U67. No difference in the EPM was observed between rapidly growing and stationary-phase E. coli B. De-energization of the cell membranes by carbonyl cyanide m-chlorophenylhydrazone (CCCP) did not affect the EPM of wild-type and deep rough mutants of E. coli; and the EPM of Cytophaga U67 and Acholeplasma laidlawii remained unaltered by CCCP when measured in their respective growth media. Extrusion of filamentous bacteriophage f1 from cells of its host, E. coli A95, caused a shift to a higher negative EPM. We also measured a variety of Gram-positive strains, all of which displayed different EPMs. When membrane fractions of E. coli were adsorbed to latex spheres, characteristic differences between the EPM of beads coated with either inner or outer membrane were observed. The results suggest that the rapid EPM analysis is a useful tool to study the net electric charge of microorganisms and to examine changes of surface properties during interaction of cells with viruses, proteins (antibody) and charged antibiotics.
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    ABSTRACT: Lipopolychacharides (LPSs) cover the surface of Gram-negative bacteria. The LPS assembly provides a penetration barrier to molecules larger than 700−1000 Da, such as many antibiotics, and when LPS molecules are released from the surface of bacteria, they cause toxic shock in the infected patient. The surface of Escherichia coli JM109 was visualized by atomic force microscopy, providing the highest resolution images of any bacterium to date (50-Å lateral and 5-Å vertical resolutions). These images indicated that LPS molecules are assembled in bundles of 600−3500 molecules. The LPS molecule is comprised of lipid A, then an inner and outer core, and an outermost region of O-antigen units. Analyses indicated that the O-antigen repeat units vary between 1 and 26 for E. coli JM109, and the fraction of the LPS molecules with zero to three repeat units made up approximately 50% of the total LPS content. A matrix of 16 LPS molecules was constructed as a representative region of the surface of E. coli. The molecular dynamics simulations of this assembly indicated that the structural components closer to the milieu experienced more movement than those closer to the interior, and that the metal ions coordinated to the inner core were indispensable for the stability of the assembly. In the absence of metal coordination to the inner core, the assembly of the LPS molecules disaggregated such that simulations beyond 67 ps could not be attempted. Simulations also indicated that the metal ions allowed for assembly of the LPS molecules one next to another in a tight formation. Such a tight assembly dramatically decreases the surface accessibility to solvent, so that there is no access for even a water molecule beyond the inner core. This structural property accounts for the aforementioned penetration barrier that is characteristic of Gram-negative bacteria.
    Journal of The American Chemical Society - J AM CHEM SOC. 01/1999; 121(38):8707-8711.
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    FEBS letters 10/1971; 16(4):343-345. · 3.54 Impact Factor