FIGURE 1.

Wild type cells accumulate increasing amounts of extracellular polyphosphate as cell density increases. A and B, cells were cultured, and the polyphosphate (polyP) concentration in the conditioned medium was measured. C, polyP from stationary phase conditioned medium was resolved on a 25% polyacrylamide gel and stained with toluidine blue (representative image of three gels). D and F, cells were cultured with 150 μm polyP (D) or the indicated concentration of polyP (F) and density (D), and the percentage of inhibition after 24 h (F) was determined. E, wild type cells were cultured in the presence or absence of 150 μm polyP for 18 h, washed twice in HL5, resuspended in fresh HL5, and counted daily. G, wild type cells were cultured in the presence or absence of triphosphate, pyrophosphate, or sodium phosphate and counted daily. All values are means ± S.E., n ≥ 4. *, p < 0.05; **, p < 0.01; ***, p < 0.001 (one-way analysis of variance).