Cation Transport in Escherichia coli VII. Potassium requirement for phosphate uptake

When Escherichia coli K-12 is grown in media containing limiting amounts of K, growth continues normally until all the extracellular K has been consumed. Thereafter the rates of growth, glucose consumption, and oxygen consumption decrease progressively, and the cell contents of K and P fall. These changes, referred to as K limitation, are all reversed by the addition of K. By specifically altering the ionic composition of the cells it was shown that these metabolic disturbances are not due to changes in the cell content of K or Na, but are directly related to the absence of K from the extracellular medium. The cell pool of inorganic P and the uptake of PO4 from the medium are low in Klimited cells and are immediately stimulated by the addition of K, suggesting that the primary effect of K limitation is to inhibit PO4 uptake. All the metabolic effects of K limitation can be attributed to inhibition of PO4 uptake. The requirement of extracellular K for PO4 uptake may be due to a coupling between the uptake of K and PO4. The requirement of microorganisms for K has been related to the role of this cation in several metabolic processes. K activates numerous cell enzymes including those engaged in protein synthesis (1, 2) and acts as an osmotic solute for the cell (3). When Escherichia coli is grown in media in which K is the limiting component, growth ceases some hours after the exhaustion of medium K even though cell K content is still quite high. Such cells, referred to as " K limited," show marked changes in their composition and metabolism. These changes cannot be interpreted in terms of known functions of K and thus are evidence for an additional role for K in cell metabolism. In this paper the alterations of the K-limited state will be described and evidence linking these alterations to interference with PO4 uptake will be presented. A preliminary report of this work has appeared (4).