Physiological Properties of a Neutralo-sensitive Mutant Derived from Facultative Alkaliphilic Bacillus sp. C-125

A neutralo-sensitive mutant (M-12) was isolated from the facultative alkaliphilic Bacillus sp. C-125. This mutant strain was able to grow to the same extent as did the parent strain above pH 8, but did not grow below pH 7.5. The same extent of oxygen uptake was shown by the cells of the parent and mutant strains at pH 10.3. On the other hand, the oxygen uptake rate was about one-fifth of that of the parent strain at pH 7. NADH-dependent oxygen uptake by everted vesicles of the mutant was lower than that of the parent strain at pH 7-7.5, while the rate at pH 8-9 was almost identical in both strains. The activity at pH 7 of cytochrome c oxidase of right-side-out membrane vesicles of the mutant strain was lower than that of the parent strain at pH 7, while both samples had almost the same enzymatic activity at pH 8.5. These results suggest that poor respiratory activities of the mutant strain at pH 7 are the reason why this mutant strain was unable to grow at neutral pH.