Bacterial wall lipids

A full discussion of the varied lipid structures found in bacterial cell walls is beyond the scope of this book but the reader will find detailed accounts in Rogers et al (1980) and Goldfine (1982). 

Gram-negative bacteria have a cell envelope containing two membranes, with the outer membrane having lipopolysaccharide in its outer leaflet. Lipopolysaccharide is complex and consists of four parts. On the outside is the O-antigen which is a polysaccharide of variable structure. This is attached to a core polysaccharide which is in two parts, an outer core and a backbone. The backbone is connected to a glycolipid, called lipid A, through a 

The cell walls and membranes of most Grampositive bacteria contain a series of highly anionic polymers. Quantitatively one of the most important of these is teichoic acid which can be covalently linked to a glycolipid to give a lipoteichoic acid (Fig. 2.10). An alternative type of anionic polymer, which is found in Gram-positive bacteria such as Micrococcus lysodeikticus, is succinylated lipo-mannan (Fig. 2.10). Like teichoic acid, the lipo-mannan is embedded in the membrane by linkage to a diacylglycerol moiety. 

Harwood, J.L. and Russell, N.J. (1984) Lipids in Plants and Microbes, George Allen and Unwin, Hemel Hempstead. 

Rogers, H.J., Perkins, H.R. and Ward, J.B. (1980) Microbial Cell Walls and Membranes, Chapman and Hall, London. 

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Dworzanski, J. R Berwald, L. McClennen, W. H. Meuzelaar, H. L. C. Mechanistic aspects of the pyrolytic methylation and transesterification of bacterial cell wall lipids. /. Anal. Appl. Pyrolysis 1991,21,221-232. 

Hydroxy or a-hydroxy acids have been shown to occur in sphingolipids, skin lipids, wool wax, bacterial cell wall lipids and in some seed oils. 3-Hydroxy or 3-hydroxy acids are present in bacterial lipids. 

The second stage occurs in the cytoplasmic membrane and is concerned with transporting the precursors from the cytoplasm to the wall. The key molecule responsible for the translocation is the lipid carrier, undecaprenyl phosphate (Figure 1.11). This highly lipophilic molecule is a C55-iso-prenoid alcohol phosphate. It is involved in the synthesis of several other bacterial wall components, for example the O side chains of lipopoly-... 

Unprotected membrane of some cells, compare walls (bacterial) and rigid lipids (archaea)... 

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]. 

Among the important glycolipids, which are combinations of carbohydrate and lipid, are the cerebrosides and gangliosides. These are constituents of brain and nervous tissue and are usually considered with lipids because they are water-insoluble. Water-soluble polymers of high relative molecular mass containing lipid and carbohydrate, known as lipopolysaccharides, are found in bacterial cell walls. 

Cells are the basic units for all living organisms. All cells are bounded by a membrane, and bacterial and plant cells have a cell wall. The membrane protects the cell from the outside environment. It consists of a lipid bilayer (Fig. A2.1). The function of the membrane is to control materials that enter and exit the cell and enable biochemical reactions to take place within the cell. 

Evidence of a role of lipid peroxidation in the cellular toxicity of ozone has been obtained in in vitro studies in which human red cells were exposed to this oxidant gas. The possibility that lipid peroxidation is responsible for altered permeability of bacterial cell walls after ozone exposure was proposed by Scott and Lesher and has since been con-... 

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