Effect of Ca2+ and K+ on the intracellular pH of an Escherichia coli L-form.

The L-form NC7, derived from Escherichia coli K12, grew in a complex medium containing 0·2 M-CaCl2 as osmotic stabilizer, but not at pH values above 7·8. The cessation of growth at alkaline pH was not due to cell death. In complex media containing K+ or Na+, the L-form grew over a wide pH range. Growth at alkaline pH was inhibited by 1 mM-amiloride, indicating that Na+/H+ antiport activity was required for growth at alkaline pH. The internal pH (pHi) of the L-form in media containing K+, Na+ or Ca2+ was constant at about 7·8 to 8·0 at external pH (pHo) values of 7·2 and 8·2. The rates of O2 consumption by intact cells, lactate oxidation by membrane vesicles from cells grown in Ca2+-containing medium, and cell division were all strongly repressed under alkaline conditions.