Levels of cyclic-2,3-diphosphoglycerate in Methanobacterium thermoautotrophicum during phosphate limitation

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Abstract
Batch-grown M. thermoautotrophicum cells grew nonexponentially in the absence of exogenous Pi until intracellular cyclic 2,3-diphosphoglycerate (cyclic DPG) had fallen below 2 .mu.mol/g (dry wt), the limit of detection. Growth resumed immediately upon transfer to medium containing Pi. Cyclic DPG levels were also below detection in Pi-limited chemostat cultures operating at a dilution rate of 0.173 h-1 (4-h doubling time), with reservoir Pi concentrations below 200 .mu.M. At this dilution rate, the Pi concentration in the culture was 4 .mu.M. An H2-limited steady state was achieved with 400 .mu.M Pi in the inflowing medium (67 .mu.M in the culture). The cyclic DPG content of these cells was 72-74 .mu.mol/g, .apprx. 1/3 the amount in batch-grown cells. The specific growth rate accelerated immediately to 0.36 h-1 (1.9-h doubling time) under washout conditions at high dilution rate. The cellular content of cyclic DPG declined over a 2 h-period, and then increased rapidly as the Pi level in the medium approached 200 .mu.M. Expansion of the cyclic DPG pool coincided with a marked increase in Pi assimilation. Evidently, M. thermoautotrophicum accumulated cyclic DPG only when Pi and H2 were readily available.