Nitric Oxide Enters Quorum Sensing via the H-NOX Signaling Pathway in Vibrio parahaemolyticus.

Takahiro Ueno,Jonathan T. Fischer,Elizabeth M. Boon

doi:10.3389/fmicb.2019.02108

Abstract

Nitric oxide (NO) plays a major role in the regulation of mammalian biological functions. In recent years, NO has also been implicated in bacterial life cycles, including in the regulation of biofilm formation, and the metabolism of the bacterial second messenger signaling molecule cyclic-di-GMP. In a previous study, we reported the discovery of an NO-responsive quorum sensing (QS) circuit in Vibrio harveyi. Here, we characterize the homologous QS pathway in Vibrio parahaemolyticus. Spectroscopic analysis shows V. parahaemolyticus H-NOX is an NO sensory protein that binds NO in 5/6-coordinated mixed manner. Further, we demonstrate that through ligation to H-NOX, NO inhibits the autophosphorylation activity of an H-NOX-associated histidine kinase (HqsK; H-NOX-associated quorum sensing kinase) that transfers phosphate to the Hpt (histidine-containing phosphotransfer protein) protein LuxU. Indeed, among the three Hpt proteins encoded by V. parahaemolyticus, HqsK transfers phosphate only to the QS-associated phosphotransfer protein LuxU. Finally, we show that NO promotes transcription of the master quorum sensing regulatory gene opaR at low cell density.

Highlights

Quorum sensing (QS) is a cell-to-cell communication system utilized by bacteria to assess their population density and to coordinate population-wide changes in gene expression
Many QS systems in Vibrio species consist of an AI synthase, a corresponding AIsensing histidine kinase (HK), and a cytoplasmic response regulator (RR)
We have demonstrated that Vp HqsK transfers phosphate to LuxU, but since many HKs can transfer phosphate to multiple partners, there remained a possibility that this HqsK/LuxU phosphotransfer was not exclusive and/or that LuxU is not a cognate phosphotransfer partner for HqsK

Summary

INTRODUCTION

Quorum sensing (QS) is a cell-to-cell communication system utilized by bacteria to assess their population density and to coordinate population-wide changes in gene expression. At high cell density, elevated AI concentrations drives HK binding to the AI, which switches the function of the kinase to act predominantly as a phosphatase This leads to the removal of phosphate from the RR and causes corresponding changes in gene expression (Waters and Bassler, 2005; Bassler and Losick, 2006; Boyer and Wisniewski-Dyé, 2009). A recent study conducted in our laboratory identified a fourth arm in the V. harveyi QS circuit In this pathway, the gaseous signaling molecule nitric oxide (NO) is integrated into QS via ligation to the hemoprotein H-NOX and its partner, an H-NOXassociated hybrid HK called HqsK (H-NOX-associated quorum sensing kinase) (Henares et al, 2012). We further characterize the NO-responsive QS circuit in the pathogenic marine bacterium V. parahaemolyticus

MATERIALS AND METHODS

Findings

DISCUSSION