Bacterial Cell gram negative envelope

Duong, F., Eichler J., Price, A., Leonard, M., and Wickner W. (1997). Biogenesis of the gram-negative bacterial envelope. Cell 91, 567-573. 

Endotoxins are bacterial cell envelope constituents that, when present in pharmaceutical products, cause pyrogenic reactions sometimes resulting in lethality. The toxicity of endotoxins is directly related to their chemical composition. However, the viability of the organism is irrelevant since endotoxin derived from dead or live microbes is equally active. The classical endotoxin is lipopolysaccharide (LPS). However, peptidoglycan (PG) also displays endotoxin-like activities. LPS is found only in gram-negative bacterial outer membranes, while PG is present in the cell... 

As the main surface component of the bacterial cell envelope LPS is thought to contribute to the restrictive Gram-negative membrane permeability, allowing bacterial growth in unfavourable environments such as those that may be encountered within or on plants. The exclusion of antimicrobial substances of plant origin probably contributes to the ability of pathogenic bacteria to parasitize plants. LPS-defective mutants show increased in vitro sensitivity to antibiotics and antimicrobial peptides and the numbers of viable bacteria often decline very rapidly upon introduction into plants. LPS may also promote bacterial adherence to plant surfaces (Newman et al., 2007). 

FIGURE 9.1 Generalized structure of bacterial cell envelope. (A) Gram positive organism. (B) Gram negative organism. 

A typical example of covalently linked lipoprotein is a small protein in the outer membrane of gram-negative bacterial envelopes that contributes to the mechanical stability of the cell envelope. This lipoprotein contains only 58 amino acid residues containing three covalently attached fatty acids, all joined to the amino-terminal cysteine [18], In the cell envelope, the amino group of the carboxyl-terminal lysine is linked to a carboxyl group of peptidoglycan. Thus, the lipoprotein ties the outer membrane to the peptidoglycan layer and thereby contributes to the mechanical stability of the cell membrane. 

Figure 1 Schematic illustration of the supramolecular architecture of the three major classes of prokaryotic cell envelopes containing crystalline bacterial cell surtece layers (S-layers). (a) Cell envelope structure of Gram-negative archaea with S-layers as the only cell wall component external to the cytoplasmic membrane, (b) Cell envelope as observed in Gram-positive archaea and bacteria. In bacteria the rigid wall component is primarily composed of peptidoglycan. In archaea other wall polymers (e.g., pseudomurein or methanochondroitin) are found, (c) Cell envelope profile of Gram-negative bacteria, composed of a thin peptidoglycan layer and an outer membrane. If present the S-layer is closely associated with the lipopolysaccharide of the outer membrane. (Modified after U.B. Sleytr, P. Messner, D. Pum, and M. Sdra. Crystalline Bacterial Cell Surface Proteins. Austin, TX R.G. Landes/Academic Press, 1996. With permission.)...

Fig. 3 Diagramatic representation of gram negative bacterial cell envelope.

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