7. Bacterial cell envelopes and cell structures
Schematic illustrating some of the different arrangements for bacterial cell envelopes.
Classic Gram-positive bacteria are monoderms (contain one cell membrane in their cell envelope) with a thick peptidoglycan layer, and classic Gram-negative bacteria are diderms (enveloped by two membranes) with a thin peptidoglycan layer between the inner and outer membranes. Examples of bacteria with other cell envelope structures include Mycoplasma (monoderms without a peptidoglycan layer), Deinococcales (diderms with a thick peptidoglycan layer that lacks lipopolysaccharide), Corynebacteriales (diderms with a thick peptidoglycan layer and unique outer membrane containing mycolic acids also known as amycomembrane), and Thermotogae (diderms with a unique outer membrane, or toga, very rich in proteins). These schematic diagrams do not show certain components such as S-layers. Red squares represent N-acetylglucosamine, blue circles represent N-acetylmuramicacid, beige squares represent proteins, and lipopolysaccharides are shown in brown.
Formation of outer membrane vesicle from the outer membrane of Gram-negative bacteria.
Outer membrane vesicles, or OMVs, are secreted bilayer vesicles produced by many Gram-negative bacteria, with an average diameter of 20-200 nm. Their composition includes proteins derived from the outer membrane and periplasm, genetic material (such as DNA and RNA), lipopolysaccharides, outer membrane lipids and virulence factors. ePSORTdb contains 293 proteins that have the OMV secondary localization. OMVs are known to have functions in transferring antibiotic resistance, cell communication, survival and virulence, making these entries valuable to researchers studying these areas.
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