sRNA C263 activated by transcriptional regulator RmaE modulates the cell wall under acid stress

Small RNAs (sRNAs) play crucial roles in response to environmental stress and contribute to bacterial survival. However, the understanding of sRNA response and regulatory mechanisms in Lactococcus lactis remains limited. In this study, a novel acid-activated sRNA, C263, was identified, which enhances cell wall peptidoglycan synthesis by base pairing with the mRNA 5’ untranslated region (5’UTR) of murA, murC, and mraY. Additionally, it was observed that transcriptional regulator RmaE can activated sRNA C263 through binding to its promoter region at 5'-AAAATTTT-3'. This binding was also validated using a LacZ reporter system in vivo. The β-galactosidase activity of the strain carrying p-C263p-lacZ-rmaE was 4.72-fold higher than that of the control group. These findings indicate that the transcriptional regulator RmaE can activate sRNA C263 to regulate cell wall homeostasis in response to acid stress in L. lactis. This study offers evidence for a synergistic regulatory mechanism involving transcriptional regulators and sRNAs in the cell wall of L. lactis in response to acid stress. L. lactis serves as an improtant strain in microbial cell factories. Therefore, understanding the regulatory mechanisms of the cell wall is essential for advancing molecular engineering and genetic editing strategies in industrial microorganisms such as L. lactis.