Bacteria gram-negative, cell envelopes

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... 

In Gram-negative bacteria which are characterised by a rather complex cell envelope, the CM is also referred to as inner membrane to distinguish it from a second lipid bilayer, termed outer membrane (OM). The space between these two layers is called the periplasm (PP). In the periplasmic space, many proteins are found with a variety of functions. Some are involved in biosynthesis and/or export of cell wall components and surface structures (e.g. pili, flagellae,... 

FIGURE 14.1 Cell envelope structures of (a) Gram-negative bacteria, (b) Gram-positive... 

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). 

Cell envelope (cell wall, outer membrane) Glutaraldehyde EDTA, other permeabilizers Cross-links proteins Gram-negative bacteria removal of Mg2+, release of some LPS... 

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