THE RELATION OF ION ANTAGONISM TO THE INORGANIC NUTRITION OF LACTIC ACID BACTERIA

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Abstract
Less Zn ion is required to inhibit the growth of Lactobacillus arabinosus in an amino acid medium than in a casein hydrolyzate medium. In both media the toxicity can be relieved competitively by Mn++. Mg ion, Ca ion, and Sr ion also counteract the inhibition by Zn of L. arabinosus and L. pentosus, although they cannot replace Mn++ for growth. These ions and Mn++ are almost inactive in reversing Zn toxicity for Leuconostoc mesenteroides at the levels tested. No evidence that Mg, Ca, or Sr is essential for the growth of L. arabinosus was obtained. The magnitude of the requirement of L. arabinosus for Mn++ is decreased by Mg, Ca, or Sr ions. Mg and Ca ions exert similar sparing action on the Mn++ requirement of L. pentosus; Sr is ineffective. Mg, but not Ca or Sr, decreases the Mn++ requirement of L. mesenteroides. An extension of these expts. showed that Rb decreases the K requirement of L. mesenteroides. and that Cs decreases the K requirement of L. arabinosus. These sparing effects on the nutritional requirement for essential ions are interpreted to mean that these related ions carry out some, but not all, of the catalytic roles served by the corresponding essential ion in metabolism. The toxicity of Zn for L. arabinosus is viewed as resulting from the formation of a catalytically inactive zinc protein from this ion and some protein normally activated by Mn++, Mg, Ca, or Sr. The latter ions counteract Zn toxicity by displacing Zn ion from the protein, thus forming a catalytically active metalloprotein. Such a mechanism for the antagonistic action of ions may have wide validity. Some of its implications are discussed.
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