ABSTRACT
Representative members of all the major groups of microorganisms can be found living in saline environments. There are prokaryotic eubacteria, cyanobacteria, and halobacteria, as well as archaeobacteria; in addition, there are eukaryotic yeasts, fungi, and algae. Thus, it should be no surprise that it is commonly observed that the membrane lipid composition of halotolerant/halophilic microorganisms changes in response to alterations in external salinity. A more complete overview of microbial lipid compositions is given in Harwood and Russell, while detailed compendia of the lipid compositions of Gram-positive and Gram-negative eubacteria, cyanobacteria, yeasts, fungi, and algae can be found in Ratledge and Wilkinson. Since the increase in anionic lipids is so commonly observed, it appears that the bilayer stabilization hypothesis is likely to be generally appropriate to halotolerant/halophilic microorganisms. The generality of the hypothesis can, of course, be tested directly by determining the phase behavior of additional halotolerant/halophilic microorganisms, but predictions can also be made on the basis of lipid compositional analysis.
