Intracellular K + and cyclic diphosphoglycerate pools and transients in Methanobacterium thermoautotrophicum

Abstract

Cultivation of M. thermoautotrophicum under K + - and phosphate-limiting conditions in chemostat cultures provided evidence that this organism can grow rapidly without the need to maintain high internal concentrations of K + and cyclic diphosphoglycerate (cyclic DPG). The internal K + concentration during K + limitation was about 320 mM. For comparison, the K + concentration was near 800 mM in batch-grown cells containing about 150 mM cyclic DPG. Phosphate limitation resulted in a decline in the K + and cyclic DPG pools to 200 mM and 9 mM, respectively. Pulse addition of K + to a K + -limited chemostat culture resulted in a transient increase in cellular K + and cyclic DPG before the new growth rate was reached. A large increase in extracellular K + (from 0.02 to 1 mM) resulted in a transition to a phosphate-limited culture and a concomitant decrease in cell K + and cyclic DPG. These two components declined by approximately 100 mM and 30 mM, respectively, during the transition from K + to phosphate limitation. Pulse addition of phosphate to phosphate-limited chemostat cultures resulted in a transient expansion of the K + and cyclic DPG pools before the shiftup in growth rate occurred. These adjustments of K + to cyclic DPG levels established K + as the major cation balancing the −3 charge of cyclic DPG.