High-efficiency transformation of Streptococcus thermophilus using electroporation.

BACKGROUND Streptococcus thermophilus, one of the most important lactic acid bacteria, is widely used in food fermentation, which is beneficial to improve food quality. However, the current genetic transformation systems are inefficient for S. thermophilus S-3, which hinders its further study. RESULTS We developed three electroporation transformation methods for S. thermophilus S-3, and optimized various parameters to enhance the transformation efficiency up to 1.3 × 106  CFU/μg DNA, which was 32-fold higher than that of unoptimized. Additionally, transcriptional analysis showed that a series of competence genes in S. thermophilus S-3 were remarkedly up-regulated after optimization, indicating that improvement of transformation efficiency was attributed to the expression level of competence genes. Furthermore, to prove their potential, expression of competence genes (comEA, cbpD and comX) were employed to increase transformation efficiency. The maximum transformation efficiency was obtained by overexpression of comEA, which was 14-fold higher than that of control. CONCLUSION This is the first report of competence gene expression for enhancing transformability in S. thermophilus, which exerts a positive effect on the development of desirable characteristics strains. © 2021 Society of Chemical Industry.