Effects of pH on transformation of Bacillus subtilis with single-stranded deoxyribonucleic acid.

Variation in frequencies of transformation mediated by native and single-stranded DNA and its dependence on pH of the medium were investigated. The results indicate that the biological activity of deoxyribonucleic acid (DNA) of both configurations assayed in the presence of ethylenediaminetetraacetic acid (EDTA) increases as the pH of the transformation mixture is lowered from 7.7 to a maximum transformation frequency near pH 6.1. At this lower pH, native DNA transforms equally in medium with and without EDTA, and single-stranded DNA is 0.4 to 0.6 as active as native DNA in transforming Bacillus subtilis. A high efficiency of transformation with single-stranded DNA was observed for five markers in three recipient strains. The increased efficiency of native DNA appears to be caused by a lesser capacity of EDTA to bind magnesium at the lower pH. The increased efficiency of single-stranded DNA at pH below 7.0 results from decreased activity of a single-strand specific nuclease present in competent populations.