Heat stress adaptation in hyperthermophiles: bosynthesis of inositol-containing compatible solutes

Abstract

The accumulation of low-molecular mass organic compounds, named compatible solutes, is an efficient, widespread strategy to counterbalance increases in the external osmolarity, thereby preserving cell viability. The intracellular accumulation of compatible solutes also occurs in response to supra-optimal temperatures, and this observation led to the assumption that they play a role in the thermoadaptation process. Hyperthermophiles, organisms with optimal growth temperatures above 80ºC, have been isolated from a variety of hot habitats. Many hyperthermophiles thrive in marine geothermal areas and are slightly halophilic. As a result, they have to cope with fluctuations in the salinity of the external medium and generally accumulate compatible solutes as a defense strategy. Interestingly, these hyperthermophilic organisms show a clear preference for negatively charged solutes, such as diglycerol phosphate, di-myo-inositol 1,3’-phosphate and mannosylglycerate, over neutral or zwitterionic solutes typically found in mesophiles (glycerol, trehalose, myo-inositol, and ectoines). The question then arises whether those charged solutes were selected by organisms adapted to grow at high temperatures because they are more suitable to protect proteins and other cell components against thermal denaturation.(...)