Optimization of ultrasound-mediated DNA transfer for bacteria and preservation of frozen competent cells

Abstract： The transformation of DNA into cells is the basis of molecular biology. Common techniques include heat shock transformation, electro-transformation, conjugation, transduction, and protoplast fusion. Ultrasonic transformation technology has recently been developed to transfer DNA into competent cells. The transformation conditions, such as temperature and ultrasonic power, were studied preliminarily. However, this technique has not been widely applied because competent cells must be prepared de novo. In this study, various factors, such as ultrasonic frequency and power, were optimized for the ultrasonic transformation of Escherichia coli. The study found that the optimal conditions for ultrasonic transformation with a defined ultrasonic transformation (UT) vial were a frequency of 28 kHz and a power of 80 W. Meanwhile, this research discovered that combining the 42 C heat shock conditions with ultrasonic transformation is the most efficient method compared to using only heat shock. Additionally, the cryoprotective agents (CPAs) ratio for ultrasonic competent cells was researched and optimized. These findings provide new ideas for improving transformation efficiency and lay a foundation for expanding the application of ultrasonic transformation.