大腸菌由来L型菌RK4の生育におけるナトリウム/プロトン交互逆輸送系の役割について

Escherichia coli, L-form NC7 was able to grow over pH range 6.2-8.8 in a complex medium supplemented with 0.34 M-NaCl (NaPY medium) or 0.34 M-KCl (KPY medium). On the other hand, variant strain, L-form RK4 derived from L-form NC7 was able to grow at acidic pH range in KPY medium, but not at all under alkaline pH conditions in both the media. When the NC7 was treated with amiloride or harmaline, inhibitor of Na+ /H+ antiporter, the similar growth inhibition as those of the RK4 was observed in both the media. The Na+ /H+ antiporter activity on everted membrane vesicles from the RK4 was markedly lower than that from the NC7. However, when the RK4 was incubated in alkaline buffer (pH 8.15) significant alkalization of the intracellular pH was not observed. When melibiose. one of substrate for Na-coupled transport system, was added into KPY medium. Na+ was actively transported with melibiose and accumulated in the RK4 cells. In addition, cell swelling and lysis of the RK4 occurred when the cells were incubated in 0.34 M NaCl solution. Therefore, these findings strongly suggest that inability of growth of the RK4 in NaPY medium due mainly to insufficient activity of the Na+ /H+ antiporter in response to extrusion of the exess Na+ accumulated into the RK4 cells.