THE present report summarizes experiments establishing the relative requirements of a typical oral lactobacillus, L. acidophitus 4646 (ATCC), for magnesium and manganese ions. A number of chelating agents were tested for their ability to limit the growth of the organisms by forming nonionized complexes with these ions.Weisberger and Johnson' studied the requirements of an oral strain of L. acidophilus for growth in media of defined composition. They reported full growth in a medium containing only casein hydrolysate, tryptophane, thiamine, nicotinic acid, pantothenic acid, and mono-and dipotassium phosphates. No requirement for magnesium or manganese ion was observed. However, the growth level attained in their experiments, as measured by acid production, was low. MacLeod and Snell2 investigated the mineral requirements of a variety of lactic acid-forming bacteria, and found an almost universal demand for manganese ion; magnesium ion was in general stimulatory but not essential. EXPERIMENTAL M ATERIALS AND METHODSMedia.-Three types of media were employed. Medium I contained acid hydrolyzed casein, fortified with cysteine, tryptophane, tyrosine and phenylalanine, purines and pyrimidines, members of the B-vitamin complex, and salts A, B, and D, as described previously.3 Medium II was similar to Medium I except that it contained enzymatic casein hydrolysate, without added amino acids, purines or pyrimidines. The B-vitamins and salts A, B and D were present. Medium III was identical with I with the exception that the caseir) hydrolysate was replaced with a mixture of 19 amino acids, as described previously.4Since this investigation was concerned primarily with certain aspects of the mineral metabolism of L. acidophilus, the composition of salts A, B, and D are given below: Salts A contained KH2PO4 and KHPO4 in a concentration such that these compounds were furnished to the final media at a level of 50 mg. per cent. Salts B contained MgSO4, MnSO4, NaCl and FeSO4. The cations were furnished to the media at the following levels: Mg++, 10 micrograms per ml.; Ain++, 1 microgram per ml.; Fe++, 2 micrograms per ml.; Na+, 40 micrograms per ml. This amount of magnesium corresponds to that found in saliva; no data could be found as to the normal salivary level of manganese.
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