Development of strong lactose/galactose-inducible expression system for Lactobacillus plantarum by optimizing promoter

Abstract

The lactose-inducible expression system was widely used in bacteria due to the safety of lactose. However, the strength of its promoter was limited in lactic acid bacteria. Here, the β-galactosidase activity in Lactobacillus plantarum WCFS1 was detected at the presence of lactose and galactose. Sequence analysis showed that two β-galactosidase encoding genes lacA and lacLM were identified in the genome of Lb. plantarum WCFS1. Using green fluorescent protein as a reporter, we found that the promoter PlacA of lacA was lactose-induced, while promoter PlacLM of lacLM was lactose/galactose-induced. Furthermore, by optimizing the sequences of –35, –10 regions and ribosome binding sites of these two promoters, the maximum strength of the promoter PlacA derivative increased 10.4-fold by lactose induction, while PlacLM derivative increased 12.7-fold by lactose induction and 9.0-fold by galactose induction compared with their original promoters, respectively. When the optimized promoters were used to drive the β-galactosidase gene from Streptococcus thermophilus CGMCC 7.179, the highest β-galactosidase activity was 45.72 ± 0.44 U/mL under PlacLM-35-10 control. The strength of these promoters was also confirmed by western-blot analysis. Thereby, this study provided a set of novel lactose/galactose-inducible promoters with high expression efficiency and thus expanded the toolbox to express recombinant protein in Lb. plantarum.