Factors affecting phosphate uptake by Aerobacter aerogenes in a system relating cell numbers to 32P uptake

The uptake of phosphate, from media limited in this ion, by resting cells of Aerobacter aerogenes has been investigated and shown to be dependent upon several factors. An incubation medium composed of 10(-2)m K(+), 5 x 10(-3)m Mg(2+), 1 mg of glucose per ml, and 1 muCi of (32)PO(4) (3-) per ml, buffered at pH 6.55 with 0.05 mN-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid (HEPES), was found to stimulate optimum accumulation of (32)P-orthophosphate. The temperature of incubation, incubation time, the concentration of unlabeled orthophosphate, as well as arsenate, and several metabolic inhibitors were found to affect the accumulation. The labeled cells were collected on a membrane filter, which had been previously boiled in glass-distilled water, for measurement of the radioactivity accumulated. Under optimum conditions, as few as 20,000 cells were capable of accumulating detectable amounts of (32)P-orthophosphate in 1 hr of incubation.