SUMMARY: The growth of bacteria in chemically-defined media containing mixtures of amino-acids is less dependent upon the magnesium concentration than in simple media composed of saits, glucose or glycerol and a single source of nitrogen. In the more complex chemically-defined media growth initially increases rapidly with, and then becomes independent of, the magnesium concentration. Gram-positive bacilli jail to grow when the magnesium content of the medium is less than 0·66 p.p.m., whereas this amount of magnesium is almost sufficient to maintain maximum growth of the Gram-negative bacteria. In addition, a deficiency of magnesium (i.e. c. 1-5 p.p.m.) inhibits the cell division of the Gram-positive rod-shaped organisms, and results in the formation of filamentous cells.


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