Transformation of Bacillus amyloliquefaciens protoplasts with plasmid DNA

A method for efficient polyethylene glycol (PEG)-mediated transformation of Bacillus amyloliquefaciens protoplasts with plasmid DNA is described. The best conditions found for protoplast regeneration included using 0.45 M sucrose both during the cultivation of the cells and (as an osmotic stabilizer) during their treatment with lysozyme, whereas 0.25 M sodium-succinate was added to the regeneration plates. Under these conditions about 5–10% of input cells regenerated. The highest transformation frequency with plasmid DNA was obtained with a PEG 6000 concentration of 22.5% (w/v). Transforming B. amyloliquefaciens strains with the plasmid pUB110 isolated from B. amyloliquefaciens resulted in 2–4 · 105 transformants/μg DNA, 100–1 000-times as high as with DNA from Bacillus subtilis, suggesting a restriction barrier between the two species. Transformation of B. amyloliquefaciens with plasmids pC194 or pE194 cop-6 gave poor yields and no restriction barrier could be demonstrated for these plasmids. However, by curing pC194 from one of the transformants, a mutant strain compatible to both the plasmids could be isolated, yielding 2–3·104 transformants/μg DNA. Both laboratory and industrial B. amyloliquefaciens strains could be transformed with the procedure.