Pyoverdine-Mediated Killing of Caenorhabditis elegans by Pseudomonas syringae MB03 and the Role of Iron in Its Pathogenicity.

Anum Bashir,Lin Li,Cui Meng,Xun Yu,Tian Tian,Muhammad Ali

doi:10.3390/ijms21062198

Abstract

The pathogenicity of the common phytopathogenic bacterium Pseudomonas syringae toward Caenorhabditis elegans has been recently demonstrated. However, the major virulence factors involved in this interaction remain unknown. In this study, we investigated the nematocidal activity of P. syringae against C. elegans under iron-sufficient/limited conditions, primarily focusing on the role of the ferric chelator pyoverdine in a P. syringae–C. elegans liquid-based pathogenicity model. Prediction-based analysis of pyoverdine-encoding genes in the genome of the wild-type P. syringae strain MB03 revealed that the genes are located in one large cluster. Two non-ribosomal peptide synthetase genes (pvdD and pvdJ) were disrupted via a Rec/TE recombination system, resulting in mutant strains with abrogated pyoverdine production and attenuated virulence against C. elegans. When used alone, pure pyoverdine also showed nematocidal activity. The role of iron used alone or with pyoverdine was further investigated in mutant and MB03-based bioassays. The results indicated that pyoverdine in P. syringae MB03 is a robust virulence factor that promotes the killing of C. elegans. We speculate that pyoverdine functions as a virulence determinant by capturing environmentally available iron for host bacterial cells, by limiting its availability for C. elegans worms, and by regulating and/or activating other intracellular virulence factors that ultimately kills C. elegans worms.

Highlights

Iron is an essential trace element that is used by most microorganisms to maintain normal life activities, and it functions as a cofactor for many oxidoreductases that catalyze redox reactions while being involved in a broad range of vital biochemical processes, such as electron transfer, oxygen transport, and energy production [1,2]
As almost all of the PVD genes of P. syringae MB03 could be identified in the P. aeruginosa PAO1 genome, we used the PAO1 genome as a reference model for PVD gene annotation in MB03 by alignment analysis, with the genes being considered orthologs when they had the same clusters of orthologous groups of proteins
The results identified 5 PVD genes in PAO1 that were not present in MB03, while 29 other PVD genes were present in both strains (Table S1)

Summary

Introduction

Iron is an essential trace element that is used by most microorganisms to maintain normal life activities, and it functions as a cofactor for many oxidoreductases that catalyze redox reactions while being involved in a broad range of vital biochemical processes, such as electron transfer, oxygen transport, and energy production [1,2]. Many siderophores are composed of peptides, which are commonly synthesized by non-ribosomal peptide synthetases (NRPSs) and multi-enzyme systems, whereas other non-polypeptide siderophores are produced by NRPS-independent synthesis pathways [7,8]. Following their biosynthesis, siderophores are secreted across the cell membrane to the extracellular space to capture ferric iron from the environment, resulting in the formation of ferric-siderophore complexes that bind to the corresponding receptors on the outer membrane (OM) and transport the iron to the cytosol via a cytoplasm-directed ABC (ATP-binding cassette) transporter [9,10]. Siderophores can uptake and transfer a variety of other metals, such as aluminum, cobalt, copper, and nickel [11,12,13,14], and more than 500 siderophores with strong strain specificity having been identified in various bacterial species [15]

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