| Abstract: | The energy metabolism of an anaerobic obligate thermophile, Clostridium thermocellum, has been examined as a function of incubation temperature using 31P NMR spectroscopy. Specifically investigated were the generation and availability of ATP as a function of temperature, activation energies for key processes in energy metabolism including formation of a pH gradient across the cell membrane, transport of key nutrients, and initial steps in glycolysis, and the existence of a membrane phase transition in the intact organism. Cells generate ATP via glycolysis at all temperatures examined; hence, limitation of the energy supply is not directly responsible for the lack of growth of this organism at low temperatures. Estimations of activation energies show a distinct hierarchy in the ATP-utilizing reactions examined. Conservation of ATP hydrolysis energy as delta pH has the lowest activation energy (less than or equal to 4 kcal/mol), two transport processes exhibit 10 kcal/mol activation energies, and early phosphorylation steps in glycolysis have significantly higher activation energies (approximately 25 kcal/mol). Neither the membrane-bound ATPase responsible for formation of the pH gradient nor the permease involved in phosphate transport shows evidence of a change in behavior around the phase transition temperature determined for extracted lipids of C. thermocellum. Line widths of inorganic phosphate do show a break in behavior around 35-40 degrees C. Possible explanations for this behavior are discussed. |
