UPTAKE AND SYNTHESIS OF COMPATIBLE SOLUTES AS MICROBIAL STRESS RESPONSES TO HIGH-OSMOLALITY ENVIRONMENTS

All microorganisms possess a positive turgor, and maintenance of this outward-directed pressure is essential since it is generally considere d as the driving force for cell expansion. Exposure of microorganisms to high-osmolality environments triggers rapid fluxes of cell water al ong the osmotic gradient out of the cell, thus causing a reduction in turgor and dehydration of the cytoplasm. To counteract the outflow of water, microorganisms increase their intracellular solute pool by amas sing large amounts of organic osmolytes, the so-called compatible solu tes. These osmoprotectants are highly congruous with the physiology of the cell and comprise a limited number of substances including the di saccharide trehalose, the amino acid proline, and the trimethylammoniu m compound glycine betaine. The intracellular amassing of compatible s olutes as an adaptive strategy to high-osmolality environments is evol utionarily well-conserved in Bacteria, Archaea, and Eukarya. Furthermo re, the nature of the osmolytes that are accumulated during water stre ss is maintained across the kingdoms, reflecting fundamental constrain ts on the kind of solutes that are compatible with macromolecular and cellular functions. Generally, compatible solutes can be amassed by mi croorganisms through uptake and synthesis. Here we summarise the molec ular mechanisms of compatible solute accumulation in Escherichia coli and Bacillus subtilis, model organisms for the gram-negative and gram- positive branches of bacteria.