FIG.2.

Weak organic acids inhibit growth of ppk mutants on a variety of carbon sources. Several independent cultures were grown to stationary phase in NCE pyruvate (A) or NCE glucose (B, C, and D). Precultures of cells harboring plasmid pSPK1(ppk⁺) were supplemented with 20 μg/ml chloramphenicol. Cells were diluted 1/200 (A and C) or 1/1,000 (B and D) into liquid test medium, and cultures were incubated with shaking at 37°C. Aerobic cultures with either 25 mM potassium acetate (A) or 5 mM sodium propionate with glucose as a carbon source (B and D) are shown. In panel C, cells were grown for 2.5 doublings before adding sodium benzoate (5 mM). Error bars represent the standard deviation from triplicate cultures (A). For B, C, and D, the averages for two independent cultures are plotted, and error bars represent the differences between the two determined values. Complete genotypes are in Table 1. ppk⁺ indicates TR10,000; ppk is TT23980; ppk/pSPK1 is TT24552; rpoS is TT23985,; and ppk, rpoS is TT23989. OD₆₅₀, optical density at 650 nm.