AUTHOR=Gao He , Ma Lizhi , Qin Qin , Qiu Yue , Zhang Jingyun , Li Jie , Lou Jing , Diao Baowei , Zhao Hongqun , Shi Qiannan , Zhang Yiquan , Kan Biao 

TITLE=Fur Represses Vibrio cholerae Biofilm Formation via Direct Regulation of vieSAB, cdgD, vpsU, and vpsA-K Transcription

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.587159

DOI=10.3389/fmicb.2020.587159

ISSN=1664-302X

ABSTRACT=<p>Attached <italic>Vibrio cholerae</italic> biofilms are essential for environmental persistence and infectivity. The <italic>vps</italic> loci (<italic>vpsU</italic>, <italic>vpsA</italic>-K, and <italic>vpsL-Q</italic>) are required for mature biofilm formation and are responsible for the synthesis of exopolysaccharide. Transcription of <italic>vps</italic> genes is activated by the signaling molecule bis-(3′–5′)-cyclic di-GMP (c-di-GMP), whose metabolism is controlled by the proteins containing the GGDEF and/or EAL domains. The ferric uptake regulator (Fur) plays key roles in the transcription of many genes involved in iron metabolism and non-iron functions. However, roles for Fur in <italic>Vibrio</italic> biofilm production have not been documented. In this study, phenotypic assays demonstrated that Fur, independent of iron, decreases <italic>in vivo</italic> c-di-GMP levels and inhibits <italic>in vitro</italic> biofilm formation by <italic>Vibrio cholerae</italic>. The Fur box-like sequences were detected within the promoter-proximal DNA regions of <italic>vpsU</italic>, <italic>vpsA-K</italic>, <italic>vieSAB</italic>, and <italic>cdgD</italic>, suggesting that transcription of these genes may be under the direct control of Fur. Indeed, the results of luminescence, quantitative PCR (qPCR), electrophoretic mobility shift assay (EMSA), and DNase I footprinting assays demonstrated Fur to bind to the promoter-proximal DNA regions of <italic>vpsU</italic>, <italic>vpsA-K</italic>, and <italic>cdgD</italic> to repress their transcription. In contrast, Fur activates the transcription of <italic>vieSAB</italic> in a direct manner. The <italic>cdgD</italic> and <italic>vieSAB</italic> encode proteins with GGDEF and EAL domains, respectively. Thus, data presented here highlight a new physiological role for Fur wherein it acts as a repressor of <italic>V. cholerae</italic> biofilm formation mediated by decreasing the production of exopolysaccharide and the intracellular levels of c-di-GMP.</p>