A simple bacterial transformation method using magnesium- and calcium-aminoclays

•A simple bacterial transformation method by spreading with aminoclay was developed.•This method was successfully applied to both Gram-negative and -positive cells.•The transformation system described here was working well in a non-invasive manner.•Thus, aminoclay-mediated transformation is a convenient tool for gene manipulation.

An efficient and user-friendly bacterial transformation method by simple spreading cells with aminoclays was demonstrated. Compared to the reported transformation approaches using DNA adsorption or wrapping onto (in)organic fibers, the spontaneously generated clay-coated DNA suprastructures by mixing DNA with aminoclay resulted in transformants in both Gram-negative (Escherichia coli) and Gram-positive cells (Streptococcus mutans). Notably, the wild type S. mutans showed comparable transformation efficiency to that of the E. coli host for recombinant DNA cloning. This is a potentially promising result because other trials such as heat-shock, electroporation, and treatment with sepiolite for introducing DNA into the wild type S. mutans failed. Under defined conditions, the transformation efficiency of E. coli XL1-Blue and S. mutans exhibited ~ 2 × 105 and ~ 6 × 103 CFU/μg of plasmid DNA using magnesium-aminoclay. In contrast, transformation efficiency was higher in S. mutans than that in E. coli XL1-Blue for calcium-aminoclay. It was also confirmed that each plasmid transformed into E. coli and S. mutans was stably maintained and that they expressed the inserted gene encoding the green fluorescent protein during prolonged growth of up to 80 generations.