Polyethyleneglycol-induced transformation of Bacillus subtilis protoplasts by bacterial chromosomal DNA

Bacillus subtilis protoplasts, which in the presence of polyethyleneglycol (PEG) are transformed by plasmid DNA (Chang and Cohen 1979) can also be transformed under these conditions by chromosomal DNA. Transformation in this case occurs at a much lower frequency, not fully accounted for by the heterogeneity of this DNA. Another unexpected feature of the transformation studied, which may explain why it previously went unnoticed, is that DNA concentrations higher than 1--2 microgram/ml decrease the yield of transformants, without showing signs of general toxicity. PEG-induced protoplasts (PIP) transformation for chromosomal markers operates normally with protoplasts prepared from a non-transformable bacterial mutant. The evidence indicates that both native linear and plasmid DNAs must somehow be forced into the cells as a result of PEG action. Denatured chromosomal DNA however is almost inactive in PIP transformation. No competition between chromosomal and plasmid DNAs could be detected, when the DNA tested as inhibitor was in tenfold excess.