The effect of related ions on the potassium requirement of lactic acid bacteria.

The essential nature of K+ for growth of lactic acid bacteria has previously been established (1). The amount required for maximum growth seemed unusually high. Further investigation showed that the quantitative requirement for potassium was markedly influenced by the amounts of sodium and ammonium ions in the medium. These findings prompted an extension of the investigation to other alkali metal ions. The results of these studies, which provide examples of “ion antagonism” among the alkali metals and which are most readily interpreted as due to competitive inhibition of the essential role of potassium by related ions, are presented below.