SALT EFFECTS IN BACTERIAL GROWTH II. THE GROWTH OF BACT. COLI IN RELATION TO H-ION CONCENTRATION

Abstract

It has been shown in a previous publication (Holm and Sher-man, 1921) that sodium chloride and various other neutral salts in 0.20M concentration affected the rate of growth of Bact. coli. Using neutral salts with a common cation (sodium) but with various anions a marked difference was observed between the action of the various salts. The effect of the chlorides of sodium, potassium and ammonium seemed to be approximately the same while the calcium and iron salts tested retarded greatly or inhibited growth. These experiments were carried out at a pH of approximately 7.0 and with a salt concentration of 0.20m in 1 per cent pepton. In as much as we know that there are limiting pH values for bacterial growth, varying with different organisms, it would be of interest and value to know just to what extent this neutral salt action is affected by various H-ion concentrations In the following experiments, as in our former communication, the rate of growth was determined by the time that expired between inoculation and the first sign of turbidity. The medium used was 1 per cent pepton to which had been added various amounts of salts, and the H-ion concentration adjusted by the use of coneentrated HCl and NaOH solutions. The effects of various concentrations of NaCl at various H-ion concentrations were first tried. The H-ion and salt concentra-Published with the permission of the Secretary of Agriculture.