Transcription terminators play a role in terminating the progress of gene transcription, and are thus essential elements in the gene circuit. Terminators have two main functions: terminating gene transcription and improving the stability of gene transcripts during translation. We therefore considered the detailed characteristics of terminators in relation to their different roles in gene transcription and translation, including transcription shut‐down degree (α) and upstream mRNA protection capacity (β), and apparent termination efficiency (η) reflecting the overall regulatory effect of the terminator. Based on a dual‐reporter gene system, we constructed three terminator‐probe plasmids to investigate each characteristic in Escherichia coli. According to multiple regression analysis, the transcription shut‐down degree and the upstream mRNA protection capacity contributed almost equally to the apparent termination efficiency. Sequence analysis of 12 terminators demonstrated that the terminator sequence was dominated by GC bases, and that a high ratio of GC bases in the stem structure of terminators might be associated with a high degree of transcription shut‐down. This comprehensive characterization of terminators furthers our understanding of the role of terminators in gene expression and provides a guide for synthetic terminator design.

The antimicrobial activity of lactic acid bacteria is closely related to its metabolites. Our results showed that Lactobacillus plantarum DY‐6 had the highest antibacterial activities among the seven bacteria tested in this study. To fully understand the active antimicrobial substances in L. plantarum DY‐6, the cell‐free supernatant (CFS) were analyzed. Our data indicated that the antibacterial effect of the CFS was positively correlated with the growth of the bacteria, and the main antibacterial substances were lactic acid, acetic acid, propionic acid, caprylic acid, and decyl acid. Finally, this study demonstrated that the antibacterial active substance produced by the lactic acid bacteria could destroy the cell membrane structure of the bacteria, causing bacteria to fail to grow and reproduce normally, thereby exerting a bacteriostatic action. Taken together, our current findings would provide an effective method for rapid screening of antimicrobial substances.

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Promoters and ribosome binding sites (RBSs) are routinely applied in gene expression regulation, but their orthogonality and combinatorial effects have not yet been systematically studied in Corynebacterium glutamicum. Here, 17 core promoters and 29 RBSs in C. glutamicum were characterized, which exhibited 470-fold and 430-fold in transcriptional and translational activity, respectively. By comparing the expression of two reporter genes regulated by multiple RBSs, the RBS efficacy showed significant dependence on the gene context, besides the RBSs' strength, reflecting the poor orthogonality of RBSs. Bicistronmodified RBS (referred as bc-RBS) was adapted to C. glutamicum, which improved RBS reliability. By coupling a series of promoters with RBSs/ bc-RBSs, a much broader regulation range that spanned 4 orders of magnitude was observed compared with that of a sole element, and the contribution to gene expression of RBS was more than that of promoter. Finally, promoters and RBSs were applied as builtin elements to fine-tune the gene cluster in the arginine synthesis pathway in C. glutamicum. Compared with the original strain, more arginine (1.61-fold) or citrulline (2.35-fold) was accumulated in a 7 L bioreactor by strains with the gene expression regulation system rationally engineered. We demonstrated that, via combination of well-characterized gene elements, and overall consideration for both transcription and translation, the biosynthesis pathway can be effectively balanced, and the yield of a target metabolite can be further improved.

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