The Influence of Hydrogen-ion Concentration on Some Acid Resistant Bacteria

Fifty-three strains of bacteria have been isolated from acidulated brine. They are classified into Bacillus, Micrococcus, Sarcina, and Lactobacillus. Of these the Bacillus strains failed to grow at hydrogen-ion concentrations more acid than pH 6.20, while the Micrococcus and Sarcina forms showed a greater tolerance, producing limited growth from pH 5.22 to 5.64. Other workers describing wider limits for the genus Bacillus failed to allow for the change produced in the weakly buffered environment by the living cell. The microaerophilic Lactobacilli grew at pH 3.52. These aciduric types are not actively proteolytic.