Effects of antibiotics on the cation composition of Bifidobacterium bifidum subspecies pennsylvanicum.

Cell wall-inhibitory antibiotics caused a marked reduction of intracellular K+ and a small increase of Na+, together resulting in a decline of intracellular cation content. Chloramphenicol and tetracycline increased intracellular K+ but actinomycin decreased both Na+ and K+ content. The release and uptake of 86Rb+ were similarly affected by the antibiotics as the K+ content. The osmotic resistance of the protoplasts isolated from antibiotic-treated cells was apparently increased by inhibitors of cell wall synthesis, but decreased by inhibitors of protein synthesis. The ionophore valinomycin enhanced growth in normal and K+-rich medium, although cells released more than 90% of intracellular K+.