SUMMARY: The uptake of Mg in Mg-limited cultures of the Gram-negative is rapid and is complete some time before the onset of the stationary phase. In similar cultures of the Gram-positive and F3 growth and Mg assimilation cease at the same time and when only part of the available Mg has been utilized; thereafter efflux of the cation may occur. In these cultures, as in dilute suspensions of the bacilli in a Mg-deficient medium, viability is maintained in a high percentage of the organisms, and growth occurs on the addition of Mg even if this is delayed for 20 hr. The minimum growth-requirement for Mg varies for different Gram-positive bacilli and is particularly low for var. The response of this organism to Mg is unaffected by Mn. The Mg requirements of and F3, however, are reduced by 25 μM Mn. Although this concentration of Mn is unable to support growth of these bacilli in the complete absence of Mg, it appears to stimulate the uptake of the latter cation from dilute solutions. Mn also is assimilated during growth by both Gram-positive and Gram-negative bacteria, although less efficiently than Mg, and is incorporated into the ribosomes.


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