Effects of Salinity on Membrane Lipids and Membrane-Derived Oligosaccharides

Abstract

A common feature of the adaptive response to elevated external salinity in microorganisms is an increase in the proportion of negatively-charged lipids in their membrane(s). In Gram-negative bacteria the change is usually a rise in phosphatidylglycerol content relative to phosphatidylethanolamine, a modification that is believed to be part of the mechanism for ensuring correct membrane function under conditions of high osmolarity. The periplasmic space in Gram-negative bacteria contains membrane-derived oligosaccharides (MDO), comprised of glucose residues substituted with phosphogiycerol and phosphoethanolamine residues that are derived from phosphatidylglycerol and phosphatidylethanolamine respectively. In Escherichia coli the concentration of MDO depends on the external osmotic pressure, and it has been postulated that they are part of the osmoregulatory response. This paper describes the metabolic interrelationships between MDO and membrane phospholipids in the context of the known salt-dependent changes in lipid composition of halotolerant and halophilic eubacteria and considers whether this supports the proposed role of MDO in osmoregulation of these bacteria.