OCCURRENCE AND ROLE OF DI-MYO-INOSITOL-1,1'-PHOSPHATE IN METHANOCOCCUS-IGNEUS

Methanococcus igneus, a hyperthermophilic marine methanogen (optimum g rowth temperature of 88 degrees C) with a 25-min doubling time, synthe sizes an unusual inositol phosphodiester which is present at high intr acellular concentrations along with L-alpha-glutamate and beta-glutama te. Identification of this compound as a dimeric inositol phosphodiest er (di-myo-inositol-1,1'-phosphate) was provided by two dimensional nu clear magnetic resonance methods. The intracellular levels of all thre e negatively charged solutes (L-alpha-glutamate, beta-glutamate, and t he inositol phosphodiester) increase with increasing levels of externa l NaCl, although the inositol compound shows much smaller increases wi th increasing NaCl levels than the glutamate isomers. The turnover of these solutes was examined by (CO2)-C-13-pulse-CO2-chase experiments. The results indicated that both the beta-glutamate and the inositol ph osphodiester behaved as compatible solutes and were not efficiently me tabolized by cells as was L-alpha-glutamate. At a fixed external NaCl concentration, lower ammonium levels increased the fraction of the ino sitol dimer present in extracts. The most pronounced changes in di-myo -inositol-1,1'-phosphate occurred as a function of cell growth tempera ture. While the organism grows over a relatively wide temperature rang e, the phosphodiester accumulated only when M. igneus was grown at tem peratures of greater than or equal to 80 degrees C. Thus, this unusual compound is a non-nitrogen-containing osmolyte preferentially synthes ized at high growth temperatures.