Optimization of electrotransformation (ETF) conditions in lactic acid bacteria (LAB)

Lactic acid bacteria (LAB) play important roles in the food industry, animal husbandry and medicine which are closely related to human life. Modern gene engineering technology is the major means to reveal gene functions, study metabolic pathways and metabolomes of strains and improve the properties of strains. However, up to now, the molecular technologies that can be applied to LAB are still very scarce. One of the main reasons for this phenomenon is the low efficiency of transformation, furthermore, the transformation protocols developed are strain specific. At present, the most common method in the transformation of LAB is electrotransformation (ETF), which has relatively high transformation efficiency, convenient operation and good reproducibility. In the process of ETF, many factors may be involved in the regulation of the ETF efficiency of the strains, including the characteristics of the strains, the properties of exogenous plasmids, the parameters of electric pulse, the application of cell wall weakening agents, the composition of washing and electroporation buffers, the resuspending culture media and heat treatment. In recent years, other methods have also been utilized to boost the transformation efficiency of strains, such as combined chemical-physical methods and bacterial conjugation. Various experimental parameters and alternative technologies to ETF which may impact the transformation efficiency are summarized in this paper. This review describes some meaningful factors for the development of transformation systems, and provides direction and foundations for the optimization and establishment of novel transformation strategies of LAB.