The role of potassium transport in the generation of a pH gradient in Escherichia coli

Abstract

The role of K+ transport in the generation of a pH gradient in Escherichia coli has been investigated. In K+-depleted cells, net K+ uptake dissipated delta psi (membrane potential) and led to an increase in delta pH (pH gradient). The magnitude of the delta pH formed bore a simple relationship to the net K+ uptake and was substantially independent of the respiratory rate. In K+-replete cells, generation of a pH gradient was again K+-dependent, although no net uptake of this cation occurred. The results are discussed in terms of K+ cycling, and it is suggested that delta pH is in part a function of the rate of cycling and independent of the respiratory rate.

Inhibition of Escherichia coli growth by acetic acid: a problem with methionine biosynthesis and homocysteine toxicity

“…pH i measurements. The pH i was determined by using the distribution across the cell membrane of a radiolabelled weak acid following centrifugation (Kroll & Booth, 1981). In this method, bromododecane oil was used to separate the cell pellet from the supernatant, [7-"%C]benzoic acid (4n5 µM ; 0n1 mCi ml − ", 3n7 MBq ml − ") was used as the weak acid, and [$H]inulin (1n0 mM; 1n0 µCi ml − ", 1 kBq ml − ") was employed as an extracellular marker.…”

Acidification of intracellular pH results in neutral pH-sensitive growth of an alkalophilic Bacillus sp.

“…The cells grew continuously when K + was added before the pH shift. It has been reported that K+ is important in regulating pH;n in Escherichia coli (15,16). So we tested whether the pH;n in this strain was affected by the presence of K+ and other monovalent rations when pH)ut was shifted from 9.0 to 7.0.…”

“…The relationships between the K+-uptake and the generation of inside alkaline dpH have been reported (1,11,15,16). Acidification of the pH;n in the absence of K+ or Rb+ implies that these cations have roles in pHin regulation at neutral pH (see Table 1).…”

“…On the other hand, some alkalophilic bacteria could maintain their pHin (alkaline inside) at neutral pH even in the absence of K+ in Na + -supplemented media (9,10). These bacteria may have active K+-transport system(s) for pHin alkalinization and circulate their internal K+ as described for E. coli (15). The internal K+ concentration of B. ASSC-2 grown in P-medium (pH 9) was about 230 mM, but they could not circulate their internal K+ at neutral pH because of their low K+ transport activity at neutral pH (Figs.…”

“…So we investigated first the intracellular alkalinization system in the bacteria then the intracellular acidification system. In many bacteria, the intracellular alkalinization system consists of proton extrusion systems (mainly the primary respiratory pump) and K+-transport systems (1,11,15,16). The primary respiratory pump, the NADH oxidase system, was not affected in the presence of Na+ or K+ (24).…”