Hydrogen ion control of autolysin-dependent functions in Bacillus subtilis.

Autolysin activity in Bacillus subtilis as reflected by cell wall turnover, was found to be maximal in slightly alkaline media. When autolysis of whole cells was measured upon the addition of azide anion, it was found that maxima were exhibited at pH 6 and pH 9. Cell walls autolyzed maximally only at pH 9. In addition, the lysis of B. subtilis by nafcillin was found to be most pronounced at pH 7, whereas the cells tended to be resistant to the lysis induced by the antibiotic at pH less than 6 and pH greater than 7.9. In contrast, the maximal rate of non-lytic killing of the bacteria by nafcillin was observed to be between pH 5 and 6. When the organisms were cultured at pH 5, a decreased growth rate, accompanied by chain formation, was observed. At pH greater than 8, growth rates were low, although long chains were not present. Because the autolysin N-acetyl-muramyl-L-alanine amidase (amidase) is minimally active at pH 5 and because the cells tend to form long chains it is suggested that the enzyme is involved in cell separation. The amidase is also primarily responsible for cell wall turnover and susceptibility to the lytic effects of nafcillin.