The OM is closely attached to the PGW by multiple covalent crosslinks, so the OM and PGW operate as a functional unit. The envelope of gram-negative bacteria comprises an inner cytoplasmic membrane (CM), a peptidoglycan wall (PGW) and an outer membrane (OM). Here I extend this argument with an emphasis on gram-positive bacteria. I have previously argued that it does not, based on compelling evidence from gram-negative bacteria ( Erickson, 2017). An important question is whether constriction of the cell envelope at cell division needs to overcome the turgor pressure. The higher osmolality of the cytoplasm relative to the outside growth medium causes it to generate a turgor pressure on the cell envelope.
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An isoosmotic periplasm would be especially important for cell division, since it would allow CM constriction and PGW synthesis to avoid turgor pressure.īacterial cytoplasm has a high concentration of proteins and nucleic acids, plus their neutralizing counterions and various small molecule osmolytes. The 0.5 M fixed charge density is similar to that of proteoglycans in articular cartilage, suggesting a comparability ability to support pressure. This approximately balances the excess osmolality of the cytoplasm that would produce a turgor pressure of 19 atm. The fixed anionic charge density of teichoic acids in the periplasm is ∼0.5 M, which would bring in ∼0.5 M Na + neutralizing ions. I then present a semi-quantitative analysis of how teichoic acids could support a periplasm that is isoosmotic with the cytoplasm. Here I suggest that a periplasmic space is probably essential in order for the periplasmic proteins to function, including especially the PBPs that remodel the peptidoglycan wall. No comparable studies have been done for gram-positive bacteria. There is strong evidence for gram-negative bacteria that a periplasm exists and is isoosmotic with the cytoplasm. The cell membrane (CM) cannot support a large turgor, so there are two possibilities for transferring the pressure to the peptidoglycan cell wall (PGW): (1) the CM could be pressed directly against the PGW, or (2) the CM could be separated from the PGW by a periplasmic space that is isoosmotic with the cytoplasm. The cytoplasm of bacteria is maintained at a higher osmolality than the growth medium, which generates a turgor pressure. Department of Cell Biology, Duke University Medical Center, Durham, NC, United States.
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