A quantitative analysis of the Cl? dependence of growth of Halobacillus halophilus was performed. Optimal growth rates were obtained at Cl? concentrations of between 0.5 and 2.0 M, and the final yield was also strictly dependent on the Cl? concentration. Br? but not I?, SO4 2?, NO2 ?, SO2 ?, OCN?, SCN?, BO2 ?, or BrO3 ? could substitute for Cl?. To analyze the function of chloride, chloride concentration was determined. At low external Cl? (Cle ?) concentrations, the growth rate was low and Cl? was excluded from the cytoplasm; increasing the Cle ?concentration led to an increase in the growth rate and an energy-dependent uptake of Cl?, thus decreasing the Cle ?/internal Cli ? gradient from ≥10 at 0.1 M Cle ? to a nearly constant value of 2 at Cle ? concentrations which allowed optimal growth. Two membrane proteins with apparent molecular masses of 31 and 16 kDa which were identified to be specific for Cl?-grown cultures are possible candidates for a chloride uptake system.
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