Identification of a Key Amino Acid of LuxS Involved in AI-2 Production in Campylobacter jejuni

Paul Plummer,Masato Akiba,Qijing Zhang,Jinge Zhu,Dehua Pei

doi:10.1371/journal.pone.0015876

Paul Plummer, Masato Akiba + Show 3 more

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https://doi.org/10.1371/journal.pone.0015876

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Journal: PloS one	Publication Date: Jan 11, 2011
Citations: 73	License type: CC BY 4.0

Affiliation: Iowa State University, The Ohio State University

Abstract

Autoinducer-2 (AI-2) mediated quorum sensing has been associated with the expression of virulence factors in a number of pathogenic organisms and has been demonstrated to play a role in motility and cytolethal distending toxin (cdt) production in Campylobacter jejuni. We have initiated the work to determine the molecular basis of AI-2 synthesis and the biological functions of quorum sensing in C. jejuni. In this work, two naturally occurring variants of C. jejuni 81116 were identified, one producing high-levels of AI-2 while the other is defective in AI-2 synthesis. Sequence analysis revealed a G92D mutation in the luxS gene of the defective variant. Complementation of the AI-2− variant with a plasmid encoded copy of the wild-type luxS gene or reversion of the G92D mutation by site-directed mutagenesis fully restored AI-2 production by the variant. These results indicate that the G92D mutation alone is responsible for the loss of AI-2 activity in C. jejuni. Kinetic analyses showed that the G92D LuxS has a ∼100-fold reduced catalytic activity relative to the wild-type enzyme. Findings from this study identify a previously undescribed amino acid that is essential for AI-2 production by LuxS and provide a unique isogenic pair of naturally occurring variants for us to dissect the functions of AI-2 mediated quorum sensing in Campylobacter.

Highlights

The role of quorum sensing in the adaptation and colonization of bacterial pathogens has been of increasing interest over the last decade
The 81116 strain maintained in our laboratory was found to be deficient in AI-2 synthesis when assessed by the V. harvyei AI-2 bioassay and compared to the bioluminescence obtained with other C. jejuni isolates and the negative controls
Despite this considerable genome stability, the data presented clearly demonstrates the presence of a single nucleotide substitution in the open reading frame of the luxS gene of 81116AI2- that results in a single amino acid substitution and the loss of AI-2 phenotype

Summary

Introduction

The role of quorum sensing in the adaptation and colonization of bacterial pathogens has been of increasing interest over the last decade. [1,2,3] Examples of such changes include regulation of adherence, motility, toxin production and expression of type three secretion systems in a variety of bacterial species. While the quorum sensing mechanisms of Gram-positive bacteria are often associated with the production and sensing of modified peptide signals, the autoinducers of Gram-negative bacteria are more commonly acylhomoserine lactones[11,12]. Another form of quorum-sensing, mediated by autoinducer-2, has been described as a highly conserved inter-species mechanism of communication with genetic conservation over a large number of both Gram-positive and Gram-negative bacteria [12,13]. DPD spontaneously cyclizes to form a mixture of several furanones which are collectively referred to as AI-2

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