Characterization of endogenous constitutive promoters from Lactobacillus salivarius for finely-tuning gene expression

Lactobacillus salivarius is an important probiotic lactic acid bacterium that plays a major role in innate and ac-quired immunity. It has gained much attention in metabolic engineering and synthetic biology owing to its probiotic properties. However, few well-characterized constitutive promoters are available to modulate L. salivarius gene expression. Here, a pool of L. salivarius endogenous constitutive promoters was identified using RNA sequencing analysis. The promoters were sorted based on their transcript levels. The application potential of the promoters was evaluated using a fluorescence reporting system. This study provides the first well -characterized endogenous constitutive promoter library from L. salivarius, which has a potential for use as a basic toolbox in various lactic acid bacteria applications.