FIG 2.

Theoretical time for the ratio between the external and cytoplasmic concentrations of a solute to reach 90 or 99% of its steady position, where influx just balances dilution caused by growth in exponentially growing cells of a typical Gram-negative bacterium and a typical Gram-positive bacterium as a function of the permeability coefficient. The solid lines are the t₉₉ plots of equation 17 for Gram-positive bacterial (gray) and Gram-negative bacterial (black) cell surface area and cytoplasmic volume (Table 2). In both cases, the bacteria were assumed to be growing rapidly with a doubling time of 30 min. The symbols (□, Gram-positive bacteria; Δ, Gram-negative bacteria) show the t₉₉ values calculated using equation 17 for the permeability coefficients given in Table 3, with the addition of one further example: 4.3 × 10⁻⁷ cm · s⁻¹, calculated for the cell envelope of Staphylococcus epidermidis and the unprotonated form of erythromycin at 37°C and pH 7.8 from uptake data from Goldman and Capobianco (65). The dashed lines show equivalent plots of 90% equilibration times from the analogous equation, t₉₀ = [−ln 0.1]/[(PA/V₃) + μ] = 2.30/[(PA/V₃) + μ], for Gram-positive bacterial cells (gray) and Gram-negative bacterial cells (black).