Effect of K+ on the membrane functions of an alkalophilic Bacillus

We have examined the involvement of K+ in the membrane functions of a facultatively alkalophilic Bacillus at neutral and alkaline pH. The effects of K+ on membrane functions, such as maintenance of the membrane potential, leucine uptake and respiratory activity, were dependent on the external pH. K+ uptake, which induced alkalinization of the cytoplasm, is suggested to be electrogenic at neutral pH and 'electroneutral' at alkaline pH, resulting in a similar level of net accumulation. We suggest that the bacterial membrane is highly permeable to K+ at neutral pH, compared to alkaline pH, which results in a pH-dependent effect of K+ on the above membrane functions.