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(−), SO(4)(2−), NO(2)(−), SO(2)(−), OCN(−), SCN(−), BO(2)(−), or BrO(3)(−) 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.