New method for electroporation of Lactobacillus species grown in high salt

We here describe a new method for electroporation of Lactobacillus species, obligately homofermentative and facultatively heterofermentative, based on the cell-wall weakening resulting from growth in high-salt media. For L. casei, optimum transformation efficiency of up to 10⁵ transformants per microgram of plasmid DNA was achieved following growth in the presence of 0.9M NaCl. Plasmids of different sizes and replication origins were also similarly transformed. These competent cells could be used either directly or stored frozen, up to 1month, for future use, with similar efficiency. This protocol was assayed with different Lactobacillus species: L. delbrueckii subsp. lactis, L. paracasei, L. plantarum and L. acidophilus, and it was found that they were transformed with similar efficiency.