Some Mineral Requirements of the Lactic Acid Bacteria*

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& (5), while manganese is essential for growth of Lactobacillus plantmum (6), and is stimulat,ory, in crude media, to Lactobadus casei (7) and various other lactic acid bacteria (8). The extensive use of lactic acid bacteria and purified media for the assay of vitamins and amino acids (1) makes knowledge of their mineral requirements of special importance. Such a study is made difficult, however, by the complexity of the nutritive requiremenm of these organisms. Complex media suitable for their growth usually contain, as contaminants, sufficient essential mineral elements to permit limited or extensive growth even though none of the mineral is added, and the presence of large amounts of organic materials renders ineffective many of the procedures used in other investigations for removal of traces of inorganic ions. Recently, it was shown (9) that contaminating traces of manganese could be removed from a medium by permitting a manganese-requiring organism, Lactobacillus arabinosus, to grow in the medium for 24 hours. After subsequent removal of the organism and reinoculation, growth occurred only if manganese were added to the medium. This biological method of removing trace impurities, which has been employed occasionally in the past (cf. (lo)), has been applied below to a study of the Mn ++, Mg++, Fe++, K+, and POd requirements of several species of lact.ic acid bacteria. Previous work (11) has indicated that moderate amounts of citrate are toxic for these organisms; 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.