Expression of Hemolysin Is Regulated Under the Collective Actions of HapR, Fur, and HlyU in Vibrio cholerae El Tor Serogroup O1.

He Gao,Jialiang Xu,Baowei Diao,Hongqun Zhao,Biao Kan,Xin Lu,Jie Li,Yiquan Zhang,Jing Lou,Qiannan Shi

doi:10.3389/fmicb.2018.01310

Abstract

The biotype El Tor of serogroup O1 and most of the non-O1/non-O139 strains of Vibrio cholerae can produce an extracellular pore-forming toxin known as cholera hemolysin (HlyA). Expression of HlyA has been previously reported to be regulated by the quorum sensing (QS) and the regulatory proteins HlyU and Fur, but lacks the direct evidence for their binding to the promoter of hlyA. In the present work, we showed that the QS regulator HapR, along with Fur and HlyU, regulates the transcription of hlyA in V. cholerae El Tor biotype. At the late mid-logarithmic growth phase, HapR binds to the three promoters of fur, hlyU, and hlyA to repress their transcription. At the early mid-logarithmic growth phase, Fur binds to the promoters of hlyU and hlyA to repress their transcription; meanwhile, HlyU binds to the promoter of hlyA to activate its transcription, but it manifests direct inhibition of its own gene. The highest transcriptional level of hlyA occurs at an OD600 value of around 0.6–0.7, which may be due to the subtle regulation of HapR, Fur, and HlyU. The complex regulation of HapR, Fur, and HlyU on hlyA would be beneficial to the invasion and pathogenesis of V. cholerae during the different infection stages.

Highlights

Vibrio cholerae, a Gram-negative and curved bacterium, is the causative agent of the diarrheal disease cholera (Clemens et al, 2017)
We showed that the highest transcription of hlyA occurs at early mid-logarithmic growth phase due to the collective and elaborate regulation of HapR, Fur, and HlyU, suggesting that HlyA would only function during the early mid-logarithmic growth phase in V. cholerae
The results showed that the wild type (WT)/pBAD24 and all of the complementary mutants exhibit α-type hemolysis, but hapR/pBAD24 and fur/pBAD24 manifest β-type hemolysis

Summary

Introduction

A Gram-negative and curved bacterium, is the causative agent of the diarrheal disease cholera (Clemens et al, 2017) This pathogen expresses various key virulence factors, including major ones, such as cholera toxin (CT), toxin co-regulated pilus (TCP), flagellum, and cholera hemolysin (HlyA; Almagro-Moreno et al, 2015; Benitez and Silva, 2016; Clemens et al, 2017). HlyA, an extracellular pore-forming toxin, is expressed in the El Tor biotype and most of the non-O1/non-O139 isolates (Yamamoto et al, 1990a; Singh et al, 2001; Diep et al, 2015) It possesses various biological activities including hemolytic activity, lethality, cardiotoxicity, cytotoxicity, and enterotoxicity (Ichinose et al, 1987; Benitez and Silva, 2016).

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