The influence of magnesium on cell division. 3. The effect of magnesium on the growth of bacteria in simple, chemically defined

SUMMARY: In simple chemically defined media all of 15 bacteria failed to grow in the complete absence of magnesium. The concentration of magnesium for maximum growth was dependent upon the Gram reaction of the individual species examined, the magnesium requirements of the Gram-positive organisms being some ten times greater than the requirements of the Gram-negative organisms. In contrast to the observations made in more complex media (peptone water), normal cell division occurred in chemically defined media containing suboptimal amounts of magnesium. It is suggested that magnesium is involved in the synthesis of bacterial protoplasm as well as cell division and, in simple chemically defined media, the synthetic reactions require the higher magnesium concentration. It has been shown (Webb, 1949) that magnesium is essential for the normal cell division of the rod-shaped bacteria growing in a peptone water medium, and that i t also stimulates the growth of these organisms. The Gram-positive bacteria examined required a greater magnesium concentration for normal growth and cell division than did the Gram-negative bacteria. In an attemp