Occurrence of 1-Glyceryl-1- myo -Inosityl Phosphate in Hyperthermophiles

Abstract

ABSTRACT The accumulation of compatible solutes was studied in the hyperthermophilic bacterium Aquifex pyrophilus as a function of the temperature and the NaCl concentration of the growth medium. Nuclear magnetic resonance analysis of cell extracts revealed the presence of α- and β-glutamate, di-mannosyl-di- myo -inositol phosphate, di- myo -inositol phosphate, and an additional compound here identified as 1-glyceryl-1- myo -inosityl phosphate. All solutes accumulated by A. pyrophilus are negatively charged at physiological pH. The intracellular levels of di- myo -inositol phosphate increased in response to supraoptimal growth temperature, while α- and β-glutamate accumulated in response to osmotic stress, especially at growth temperatures below the optimum. The newly discovered compound, 1-glyceryl-1- myo -inosityl phosphate, appears to play a double role in osmo- and thermoprotection, since its intracellular pool increased primarily in response to a combination of osmotic and heat stresses. This work also uncovered the nature of the unknown compound, previously detected in Archaeoglobus fulgidus (L. O. Martins et al., Appl. Environ. Microbiol. 63:896-902, 1997). The curious structural relationship between diglycerol phosphate (found only in Archaeoglobus species), di- myo -inositol phosphate (a canonical solute of hyperthermophiles), and the newly identified solute is highlighted. This is the first report on the occurrence of 1-glyceryl-1- myo -inosityl phosphate in living systems.