Dependence of the growth of pH-sensitive mutants of a facultatively alkalophilicBacilluson the regulation of cytoplasmic pH

A facultatively alkalophilic Bacillus strain, YN-2000, is able to grow over a wide pH range, from 7.0–10.5, and was suggested to regulate its cytoplasmic pH by alkalinization and acidification systems at neutral and alkaline pH, respectively [9]. Two kinds of pH-sensitive mutants were isolated after treatment with N-methyl-N′-nitro-N-nitrosoguanidine. One mutant was neutral-sensitive and unable to grow below pH 8. The other was alkaline-sensitive and unable to grow above pH 9. The neutral- and alkaline-sensitive mutants were suggested to be unable to regulate cytoplasmic pH at neutral and alkaline pH, respectively.