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Although the requirements of several lactic acid bacteria for organic nutrients are known in considerable detail (1,2), knowledge of the mineral nutrition of this same group of bacteria is scanty. In chemically defined media, the mineral mixture most commonly used has been that of Speakman (3), which contains K+, Naf, Mg++, Mn++, Fe++, PO,“, S04* and Clions. Of these, previous investigations have shown that potassium is required for growth of Streptococcus faecalis (4) and LQctobacillus cas data below indicate that this toxicity is due to the complex-forming action of citrate with bivalent metallic ions, since it can be prevented by addition of adequate amounts of manganese and magnesium ions.
MacLeod et al. (Mon,) studied this question.