AUTHOR=Hwang Seung-Ho , Park Jin Hwan , Lee Byungho , Choi Sang Ho 

TITLE=A Regulatory Network Controls cabABC Expression Leading to Biofilm and Rugose Colony Development in Vibrio vulnificus

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.03063

DOI=10.3389/fmicb.2019.03063

ISSN=1664-302X

ABSTRACT=<p>Biofilms provide bacteria with protection from environmental stresses and host immune defenses. The pathogenic marine bacterium <italic>Vibrio vulnificus</italic> forms biofilms and colonizes environmental niches such as oysters. The <italic>cabABC</italic> operon encodes an extracellular matrix protein CabA and the corresponding type I secretion system, which are essential for biofilm and rugose colony development of <italic>V. vulnificus</italic>. In this study, molecular biological analyses revealed the roles of three transcriptional regulators BrpR, BrpT, and BrpS in the regulatory pathway for the <italic>cabABC</italic> operon. BrpR induces <italic>brpT</italic> and BrpT in turn activates the <italic>cabABC</italic> operon in a sequential cascade, contributing to development of robust biofilm structures. BrpT also activates <italic>brpS</italic>, but BrpS represses <italic>brpT</italic>, constituting a negative feedback loop that stabilizes <italic>brpT</italic> expression. BrpT and BrpS directly bind to specific sequences upstream of <italic>cabA</italic>, and they constitute a feedforward loop in which BrpT induces <italic>brpS</italic> and together with BrpS activates <italic>cabABC</italic>, leading to precise regulation of <italic>cabABC</italic> expression. Accordingly, BrpS as well as BrpT plays a crucial role in complete development of rugose colonies. This elaborate network of three transcriptional regulators BrpR, BrpT, and BrpS thus tightly controls <italic>cabABC</italic> regulation, and contributes to successful development of robust biofilms and rugose colonies in <italic>V. vulnificus</italic>.</p>