Conserved mycobacterial sRNA B11 regulates lipooligosaccharide synthesis at post-transcriptional level

Abstract

Extractable glycolipids of mycobacteria, such as lipooligosaccharides (LOS), play key roles in responding to environmental stress and altering the host immune response. However, although the biosynthesis of LOS is likely controlled at multiple levels to ensure proper composition of the cell wall, the key regulators are currently unknown. Here, we studied B11, a conserved mycobacterial sRNA, and found that it post-transcriptionally regulates LOS synthesis in Mycobacteria marinum. Deletion of B11 alters the colony morphology and RNA sequencing combined with mass spectrometry identified several genes in the LOS synthesis locus that are regulated by B11. We found that B11 uses the cytosine-rich loops of its rho-independent transcriptional terminator to interact with guanine-tracks adjacent to the ribosome binding sites of its target genes, thereby impeding translation and promoting mRNA degradation by RNase E. These comprehensive functional studies of mycobacterial sRNA B11 demonstrate sRNA-based regulation of cell wall synthesis in mycobacteria. ImportanceDespite being identified for more than a decade, the functional characterization and regulatory mechanisms of mycobacterial sRNAs remain largely unexplored. We present here the most comprehensive functional study of mycobacterial sRNAs to date, employing convincible target screening using multifaceted experimental approaches and phenotype analysis. Our work reveals how synthesis of mycobacterial lipooligosaccharides (LOS), one of the crucial extractable glycolipids involved in environmental stress response and host immune modulation, is regulated at the post-transcriptional level by the conserved sRNA B11. Furthermore, our discovery of a highly conserved sRNA exhibiting distinct functions across mycobacterial species exemplifies divergent functional evolution among sRNAs.