Effects of growth conditions on the ion composition of Bifidobacterium bifidum subsp. pennsylvanicum.

The cation content of Bifidobacterium bifidum subsp. pennsylvanicum was markedly influenced by the washing procedure of the cells, by the growth phase and the temperature, and by the composition of the culture medium. Optimal retention of cations was achieved by washing with 0.25 M MgCl2 at 20C. The intracellular Na+ concentration rose during growth in normal medium to a constant value in the stationary phase, the K+ concentration rose in the exponential phase, but fell in the stationary phase. Cells from 29-C cultures contained more Na+ and less K+ in the stationary phase than did cells from 37-C cultures, but the total cation content was the same at 29 and 37C. Intracellular Na+ and K+ concentrations were dependent on the concentrations in the medium and on its osmolarity. The intracellular Na+/K+ ratio varied from 0.04 to 2.3. The concentrations of Na+,K+ and phosphate in the medium hardly affected growth. Mg2+-deficiency of the medium markedly decreased the concentration of Mg2+ within the cell; its concentration in the cell sap was greatly affected, but the amount of sedimentable, bound Mg2+ only slightly. The content of K+ within the cell decreased in Mg2+-deficient medium, but the concentration of Na+ did not. Omission of Tween 80 as well as its substitution by Tween 20 caused a decrease of intracellular K+. Cells from Tween 40 and Tween 60 cultures additionally contained markedly less Na+.