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Knockout mutations of the LuxR regulator PFL_3627 and the sRNA phrS causes pleiotropic effects on the biocontrol bacterium Pseudomonas protegens Pf-5

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posted on 2022-03-28, 15:50 authored by Huayu Qin
The Pseudomonas protegens Pf-5 (previously known as P.fluorescens Pf-5) has shown potential as a biological control agent against plant pathogenic bacteria, fungi and nematodes. The production of anti-pathogen compounds and rhizosphere colonisation are two of the key traits that determine its biocontrol competency. Genetic and biochemical studies of secondary metabolite biosynthesis combined with analysis of the genome sequence have clarified many aspects of the production of anti-pathogen compounds in Pf-5. However, there is only very limited data on the molecular factors important for rhizosphere colonisation. Successful rhizosphere colonisation is likely influenced by two features: motility and biofilm formation. In many bacteria, motility and biofilm are both regulated by quorum sensing (QS) and small RNAs (sRNA). This study focuses on a LuxR solo regulator PFL_3627 involved in QS, and a sRNA phrS. Gene knockouts of both of these genes reveal they have pleiotropic effects on both biofilm formation and motility. A microarray analysis of a PFL_3627 mutant revealed a large number of genes that are up- or down-regulated by this regulator. Generally, canonical QS regulation by LuxR is mediated by the exogenous or endogenous QS signalling molecules N-acyl-homoserine-lactone (AHL). The Pf-5 genome does not encode a LuxI homolog for AHL biosynthesis, and consistent with this no endogenous AHL production was detected using biosensor strains. An assay of exogenous addition of short or long chain AHLs suggested that the LuxR regulator PFL_3627 is not involved in sensing AHLs. Thus PFL_3627 is presumably involved in the sensing of an as yet unknown molecule, possibly of plant origin.


Table of Contents

Chapter 1. Introduction -- Chapter 2. Mutation of LuxR solo PFL_3627 in biocontrol strain Pseudomonas protegens Pf-5 facilitates early-phase biofilm formation by promoting the initial attachment and motility -- Chapter 3. The small regulatory RNA PhrS interferes with the bacterial motility and biofilm formation of biocontrol strain Psuedomonas protegens Pf-5 -- Chapter 4. Discussion & conclusion.


"December 2014" Includes bibliographical references Thesis by publication. "This thesis is presented as a partial fulfillment to the requirements for the degree of Master of Philosophy, Department of Chemistry and Biomolecular Sciences".

Awarding Institution

Macquarie University

Degree Type

Thesis MPhil


MPhil, Macquarie University, Faculty of Science and Engineering, Department of Chemistry and Biomolecular Sciences

Department, Centre or School

Department of Chemistry and Biomolecular Sciences

Year of Award


Principal Supervisor

Ian T. Paulsen

Additional Supervisor 1

Paul Haynes


Copyright Huayu Qin 2014. Copyright disclaimer: Copyright disclaimer:




1 online resource (x, 140 pages) illustrations (some colour)

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