Ikegami M, Takahashi H, Igarashi K, Kakinuma Y
Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Biosci Biotechnol Biochem. 2000 May;64(5):1088-92. doi: 10.1271/bbb.64.1088.
Enterococcus hirae grows in a broad pH range from 5 to 11. An E. hirae mutant 7683 lacking the activities of two sodium pumps, Na+-ATPase and Na+/H+ antiporter, does not grow in high Na+ medium at pH above 7.5. We found that 7683 grew normally in high Na+ medium at pH 5.5. Although an energy-dependent sodium extrusion at pH 5.5 was missing, the intracellular levels of Na+ and K+ were normal in this mutant. The Na+ influx rates of 7683 and two other strains at pH 5.5 were much slower than those at pH 7.5. These results suggest that Na+ elimination of this bacterium at acid pH is achieved by a decrease in Na+ entry and a normal K+ uptake.
平肠球菌能在5至11的广泛pH范围内生长。一株缺乏两种钠泵（Na⁺-ATP酶和Na⁺/H⁺逆向转运蛋白）活性的平肠球菌突变体7683，在pH高于7.5的高钠培养基中无法生长。我们发现7683在pH 5.5的高钠培养基中能正常生长。尽管在pH 5.5时缺乏能量依赖的钠排出，但该突变体细胞内的Na⁺和K⁺水平正常。7683及其他两株菌株在pH 5.5时的Na⁺内流速率比在pH 7.5时慢得多。这些结果表明，该细菌在酸性pH条件下通过减少Na⁺内流和正常摄取K⁺来实现Na⁺的清除。
