Phosphate transport in Pseudomonas aeruginosa Involvement of a periplasmic phosphate‐binding protein

A binding protein for inorganic phosphate was purified to apparent homogeneity from the shock fluids of phosphate‐limited Pseudomonas aeruginosa. The purified protein bound one molecule of phosphate per molecule of binding protein with an average K_d of 0.34 μM. Arsenate, pyrophosphate and polyphosphates up to 15 units long could inhibit the binding of phosphate to the binding protein, although organic phosphates, such as glucose 6‐phosphate, glycerol 3‐phosphate and adenosine 5′‐monophosphate could not. Mutants lacking the phosphate‐binding protein were isolated and shown to be deficient in phosphate transport compared with wild‐type cells. Two kinetically distinct systems for phosphate uptake could be observed in wild‐type cells, with apparent K_m values of 0.46 ± 0.10 μM (high affinity) and 12.0 ± 1.6 μM (low affinity). In contrast, only a single low‐affinity transport system was observable in mutants lacking the binding protein (K_m apparent = 19.3 ± 1.4 μM P_i), suggesting the involvement of the binding protein in the inducible high‐affinity phosphate‐uptake system of P. aeruginosa.