Identification and evaluation of a panel of strong constitutive promoters in Listeria monocytogenes for improving the expression of foreign antigens.

Attenuated Listeria monocytogenes could be a potential vaccine vector for the immunotherapy of tumors or pathogens. However, the lack of reliable promoters has limited its ability to express foreign antigens. In the present study, 21 promoters were identified from Listeria monocytogenes through RNA-seq analysis under two pH conditions of pH 7.4 and pH 5.5. Based on the constructed fluorescence report system, 7 constitutive promoters exhibited higher strength than Phelp (1.8-fold to 5.4-fold), a previously reported strong promoter. Furthermore, the selected 5 constitutive promoters exhibited higher UreB production activity than Phelp (1.1-fold to 8.3-fold). Notably, a well-characterized constitutive promoter P18 was found with the highest activity of fluorescence intensity and UreB production. In summary, the study provides a panel of strong constitutive promoters for Listeria monocytogenes and offers a theoretical basis for mining constitutive promoters in other organisms. KEY POINTS: • Twenty-one promoters were identified from L. monocytogenes through RNA-seq. • Fluorescent tracer of L. monocytogenes (P18) was performed in vitro and in vivo. • A well-characterized constitutive promoter P18 could improve the expression level of a foreign antigen UreB in L. monocytogenes.