Properties of two different Na+/H+ antiport systems in alkaliphilic Bacillus sp. strain C-125

Abstract

Na+/H+ antiport was studied in alkaliphilic Bacillus sp. strain C-125, its alkali-sensitive mutant 38154, and a transformant (pALK2) with recovered alkaliphily. The transformed was able to maintain an intracellular pH (pHin) that was lower than that of external milieu and contained an electrogenic Na+/H+ antiporter driven only by delta psi (membrane potential, interior negative). The activity of this delta psi-dependent Na+/H+ antiporter was highly dependent on pHin, increasing with increasing pHin, and was found only in cells grown at alkaline pH. On the other hand, the alkali-sensitive mutant, which had lost the ability to grow above pH 9.5, lacked the delta psi-dependent Na+/H+ antiporter and showed defective regulation of pHin at the alkaline pH range. However, this mutant, like the parent strain, still required sodium ions for growth and for an amino acid transport system. Moreover, another Na+/H+ antiporter, driven by the imposed delta pH (pHin > extracellular pHout), was active in this mutant strain, showing that the previously reported delta pH-dependent antiport activity is probably separate from delta psi-dependent antiporter activity. The delta pH-dependent Na+/H+ antiporter was found in cells grown at either pH 7 or pH 9. This latter antiporter was reconstituted into liposomes by using a dilution method. When a transmembrane pH gradient was applied, downhill sodium efflux was accelerated, showing that the antiporter can be reconstituted into liposomes and still retain its activity.

Osmosensing and osmoregulatory compatible solute accumulation by bacteria

“…Ž . et al, 1994 and Bacillus sp Kitada et al, 1994 . The protons that exchange for Na q would presumably be exported by the electron transport system, which is responsible for generating the protonmotive force.…”

Alkaline Growth pH-Dependent Increase of Respiratory and NADH-Oxidation Activities of the Facultatively Alkaliphilic StrainBacillus lentusC-125

“…It was shown that the L11/1-dependent Na + jH + antiporter rather than the L1pH-dependent Na + jH + antiporter helps to maintain the intracellular pH around neutrality. 9) The cell wall negative charges and L11/1-dependent antiporter likely contribute to keeping the intracellular pH neutral when the organism grows in an alkaline environment. These functions are probably dependent on hydrogen ions generated by respiration and accumulated around the outer surface of the cytoplasmic membrane and in the cell-wall matrix.…”

Measurement of cytoplasmic pH of the alkaliphile Bacillus lentus C-125 with a fluorescent pH probe

“…The cytoplasmic pH has also been measured from fluorescence quenching of 9-aminoacridine (Tsuchiya & Takeda, 1979;Sugiyama et al, 1985;Kitada et al, 1994). This pigment is retained effectively in cells whose cytoplasmic pH is lower than the extracellular pH.…”