Polyphosphate Metabolism in <i>Escherichia coli</i>

Polyphosphate metabolism in Escherichia coli was studied in order to determine the role of polyphosphates in energy and phosphate metabolism. Phosphate-shift experiments were performed on wild-type E. coli W3110 and on an E. coli strain mutant in the genes encoding the polyphosphate-metabolizing enzymes polyphosphate kinase (PPK) and polyphosphatase (PPX). The levels of polyphosphates were measured by [31P]NMR, and the activities of PPK and PPX were measured using enzymatic assays. During phosphate starvation, the intracellular level of polyphosphate was not detectable in E. coli W3110; the activities of PPX and alkaline phosphatase were high relative to those during exponential growth. During the shift from phosphate starvation to phosphate surplus conditions, PPX activity decreased and PPK activity and intracellular polyphosphate stores increased dramatically. These results imply an important role for polyphosphates in cellular energy and phosphate storage and in adaptation to adverse growth conditions.