Bacterial cell wall thickness

US with changing salt concentration, indicating the presence of relatively thick adsorbed layers on the sulfur particles (see Fig. 4). This, as well as surface charge density measurements showing values comparable to surface charge densities of bacterial cell walls and humic acids, support the suggestion of proteins adsorbed on the particles. In addition, electrophoretic mobility experiments showed an iso-electric point comparable to the pKa-value of carboxylic acid groups in proteins (pKa=2.3) [45]. 

We need to remember that the presence of peptidoglycans associated with the cell wall relates only to Eubacteria (except for the very particular group of the Mycoplasma), and that there are no peptidoglycans in the Archaea. The study of bacterial cell walls reveals two subsets (i) those equipped with a thick layer of peptidoglycan on the membrane and in direct contact with the external medium and (ii) those that have only one thin layer of peptidoglycan, which is separated from the external medium by an external membrane. The relative thicknesses of the layer of peptidoglycan for the two subsets are in the ratio of approximately 5 to 1. 

In Gram-negative bacteria the cell wall is only about 3 nm thick, and located in the extended periplasmatic space between the inner membrane (IM) and an additional outer membrane (OM). The lipid monolayer in the outer leaflet of the OM contains about 90% lipopolysaccharides (LPS). LPS consist of Lipid A and an oligosaccharide component, which is highly specific for individual bacterial species and phenotypes [108, 114]. 

Its chemical makeup is considered in Chapter 8. One of the layers is often referred to as the outer membrane. In some bacteria the wall may be as much as 80 nm thick and may be further surrounded by a thick capsule or glycocalyx (slime layer).13 The main function of the wall seems to be to prevent osmotic swelling and bursting of the bacterial cell when the surrounding medium is hypotonic. 

The plasma membrane of bacterial cells, other than the wall-less mycoplasmas and some archaebacteria, is surrounded by a multilayered wall which may be separated from the membrane by a thin periplasm (or periplasmic space). This can be seen most clearly in suitably prepared thin sections of cells of E. coli or other gram-negative bacteria as a relatively empty space of 11- to 25-nm thickness (Fig. 8-28).579 581 The volume of this space (which may be filled with gelled material) depends upon the osmotic pressure of the medium. In E. coli it contains 20-40% of the total... 

Structural defenses. Plants have natural features that help ward off attack by a pathogen. A thick, waxy layer on the leaf surface can stop mechanical penetration by fungi an impenetrable cell wall may impede progress of a fungus within a plant. A plant may be resistant to bacterial attack because it has small pores that bacteria cannot get through easily. Similarly, hairs on leaves or fruit of many plants may shed water, increasing resistance to diseases that need water in order to develop. 

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