Electromechanical Interactions in Cell Walls of Gram-Positive Cocci

Abstract

Isolated cell walls of Staphylococcus aureus and Micrococcus lysodeikticus were found to expand and contract in response to changes in environmental p H and ionic strength. These volume changes, which could amount to as much as a doubling of wall dextran-impermeable volume, were related to changes in electrostatic interactions among fixed, ionized groups in wall polymers, including peptidoglycans. S. aureus walls were structurally more compact in the hydrated state and had a higher maximum charge density than M. lysodeikticus walls. However, they were less responsive to changes in electrostatic interactions, apparently because of less mechanical compliance. In media of nearly neutral p H, S. aureus walls had a net positive charge whereas M. lysodeikticus walls had a net negative charge. These charge differences were reflected in Donnan distributions of mobile ions between wall phases and bulk medium phases. Cell walls of unfractionated cocci also could be made to swell and contract, and wall tonus in intact cells appeared to be set partly by electrostatic interactions and partly by mechanical tension in the elastic structures due to cell turgor pressure. The experimental results led to the conclusions that bacterial cell walls have many of the properties of polyelectrolyte gels and that peptidoglycans are flexible polymers. A reasonable mechanical model for peptidoglycan structure might be a sort of three-dimensional rope ladder with relatively rigid, polysaccharide rungs and relatively flexible polypeptide ropes. Thus, the peptidoglycan network surrounding cocci appeared to be predominantly an elastic restraining structure rather than a rigid shell.

Macromolecules that prefer their membranes curvy

“…For the vast majority of bacteria, the rigid peptidoglycan cell wall dictates cell shape, independent of the membrane composition, and is the primary structure that bears the stress of turgor pressures on the order of atmospheres (Holtje, 1998;Scheffers and Pinho, 2005). In the absence of turgor pressure, the membrane will undergo plasmolysis and separate from the cell wall into highly invaginated structures (Ou and Marquis, 1970). How does one consider the physical effects of the com- A. Cardiolipin's unique dimeric structure, with two phosphatidyl head groups and four acyl chains, is indicative of a conical shape with a small radius of curvature Rlipid and hence a preference for highly curved geometries.…”

Relation between wall teichoic acid content and Concanavalin A binding in Bacillus subtilis 168

“…So far very little is known, at least quantitatively, of the relation between wall composition and surface properties in Gram positive bacteria. There is evidence that the relationship is not fixed but depends on evironmental conditions that can affect the state of expansion of the wall material [11] and the nature of the components that are exposed at the surface [12]. That we can obtain bacteria that contain controlled proportions of teichoic acid and teichuronic acid makes it possible to begin to study this relationship.…”

Effect of Inorganic Cations on the Biocidal and Cellular Activity of Glutaraldehyde

“…Addition of salts to cell suspensions decreased cell volume, as also did Mg2+-acid glutaraldehyde solution, in contrast to either acid or alkaline glutaraldehyde without Mg2+. Changes in volume of the whole cell are considered to be due to ionic interaction of salts with the wall (Marquis 1968;Ou & Marquis 1970). Knowles (1971) suggested that an increase in turbidity of Esch.…”