Rapid DNA transformation in Salmonella Typhimurium by the hydrogel exposure method

• A protocol of Salmonella transformation using sepiolite nanofibers was optimized.
• The tested variables are: amount of sepiolite, number of cells and spreading time.
• Using the general protocol, the efficiency was about 5 × 105 per 1 μg of plasmid.
• The method is simple, rapid, and inexpensive and does not require competent cell preparation.

Even with advances in molecular cloning and DNA transformation, new or alternative methods that permit DNA penetration in Salmonella enterica subspecies enterica serovar Typhimurium are required in order to use this pathogen in biotechnological or medical applications. In this work, an adapted protocol of bacterial transformation with plasmid DNA based on the “Yoshida effect” was applied and optimized on Salmonella enterica serovar Typhimurium LT2 reference strain. The plasmid transference based on the use of sepiolite as acicular materials to promote cell piercing via friction forces produced by spreading on the surface of a hydrogel. The transforming mixture containing sepiolite nanofibers, bacterial cells to be transformed and plasmid DNA were plated directly on selective medium containing 2% agar. In order to improve the procedure, three variables were tested and the transformation of Salmonella cells was accomplished using plasmids pUC19 and pBR322. Using the optimized protocol on Salmonella LT2 strain, the efficiency was about 105 transformed cells per 109 subjected to transformation with 0.2 μg plasmid DNA. In summary, the procedure is fast, offers opportune efficiency and promises to become one of the widely used transformation methods in laboratories.