AUTHOR=Liu Xinqiang , Liu Yuanyuan , Lei Chao , Zhao Guoping , Wang Jin 

TITLE=GlnR Dominates Rifamycin Biosynthesis by Activating the rif Cluster Genes Transcription Both Directly and Indirectly in Amycolatopsis mediterranei

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00319

DOI=10.3389/fmicb.2020.00319

ISSN=1664-302X

ABSTRACT=<p>Because of the remarkable efficacy in treating <italic>mycobacterial</italic> infections, rifamycin and its derivatives are still first-line antimycobacterial drugs. It has been intensely studied to increase rifamycin yield from <italic>Amycolatopsis mediterranei</italic>, and nitrate is found to provide a stable and remarkable stimulating effect on the rifamycin production, a phenomenon known as “nitrate-stimulating effect (NSE)”. Although the NSE has been widely used for the industrial production of rifamycin, its detailed molecular mechanism remains ill-defined. And our previous study has established that the global nitrogen regulator GlnR may participate in the NSE, but the underlying mechanism is still enigmatic. Here, we demonstrate that GlnR directly controls rifamycin biosynthesis in <italic>A. mediterranei</italic> and thus plays an essential role in the NSE. Firstly, GlnR specifically binds to the upstream region of <italic>rifZ</italic>, which leads us to uncover that <italic>rifZ</italic> has its own promoter. As RifZ is a pathway-specific activator for the whole <italic>rif</italic> cluster, GlnR indirectly upregulates the whole <italic>rif</italic> cluster transcription by directly activating the <italic>rifZ</italic> expression. Secondly, GlnR specifically binds to the upstream region of <italic>rifK</italic>, which is also characterized to have its own promoter. It is well-known that RifK is a 3-amino-5-hydroxybenzoic acid (AHBA, the starter unit of rifamycin) synthase, thus GlnR can promote the supply of the rifamycin precursor by directly activating the <italic>rifK</italic> transcription. Notably, GlnR and RifZ independently activate the <italic>rifK</italic> transcription through binding to different sites in <italic>rifK</italic> promoter region, which suggests that the cells have a sophisticated regulatory mechanism to control the AHBA biosynthesis. Collectively, this study reveals that GlnR activates the <italic>rif</italic> cluster transcription in both direct (for <italic>rifZ</italic> and <italic>rifK</italic>) and indirect (for the whole <italic>rif</italic> cluster) manners, which well interprets the phenomenon that the NSE doesn’t occur in the <italic>glnR</italic> null mutant. Furthermore, this study deepens our understanding about the molecular mechanism of the NSE.</p>