Quantitative and Physiological Analyses of Chloride Dependence of Growth of Halobacillus halophilus

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⁻, SO₄²⁻, 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⁻ (Cl_e⁻) concentrations, the growth rate was low and Cl⁻ was excluded from the cytoplasm; increasing the Cl_e⁻ concentration led to an increase in the growth rate and an energy-dependent uptake of Cl⁻, thus decreasing the Cl_e⁻/internal Cl_i⁻ gradient from ≥10 at 0.1 M Cl_e⁻ to a nearly constant value of 2 at Cl_e⁻ 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.