Glass bead-based transformation method for lactic acid bacteria

Electroporation has been considered as a popular transformation method for lactic acid bacteria. However, it is inaccessible to some laboratories because of its requirement of expensive and specialized equipment. In this study, we propose a transformation method for lactic acid bacteria which does not require equipment other than that readily available in a typical laboratory. This method is based on agitation of mutanolysin-treated bacterial cells with glass beads in the presence of plasmid DNA and polyethylene glycol. By using the basic protocol of glass bead transformation, Leuconostoc dextranicum ATCC 19255 was successfully transformed with pGK12 at the frequency of 323 per mu g of plasmid DNA. Effects of many parameters on the transformation frequency were studied to optimize the transformation protocol. By using the optimized protocol of glass bead trans formation, introduction of pGK12 into mutanolysin-treated cells of several strains of lactic acid bacteria was achieved with high reproducibility and acceptable efficiency.