Type III Secretion System and Virulence Markers Highlight Similarities and Differences between Human- and Plant-Associated Pseudomonads Related to Pseudomonas fluorescens and P. putida

Abstract

dPseudomonas fluorescens is commonly considered a saprophytic rhizobacterium devoid of pathogenic potential. Nevertheless, the recurrent isolation of strains from clinical human cases could indicate the emergence of novel strains originating from the rhizosphere reservoir, which could be particularly resistant to the immune system and clinical treatment. The importance of type three secretion systems (T3SSs) in the related Pseudomonas aeruginosa nosocomial species and the occurrence of this secretion system in plant-associated P. fluorescens raise the question of whether clinical isolates may also harbor T3SSs. In this study, isolates associated with clinical infections and identified in hospitals as belonging to P. fluorescens were compared with fluorescent pseudomonads harboring T3SSs isolated from plants. Bacterial isolates were tested for (i) their genetic relationships based on their 16S rRNA phylogeny, (ii) the presence of T3SS genes by PCR, and (iii) their infectious potential on animals and plants under environmental or physiological temperature conditions. Two groups of bacteria were delineated among the clinical isolates. The first group encompassed thermotolerant (41°C) isolates from patients suffering from blood infections; these isolates were finally found to not belong to P. fluorescens but were closely related and harbored highly conserved T3SS genes belonging to the Ysc-T3SS family, like the T3SSs from P. aeruginosa. The second group encompassed isolates from patients suffering from cystic fibrosis; these isolates belonged to P. fluorescens and harbored T3SS genes belonging to the Hrp1-T3SS family found commonly in plant-associated P. fluorescens. The group of fluorescent pseudomonads is composed of ubiquitous bacteria commonly encountered in aquatic, aerial, and soil environments (1, 2). Under iron limitation, members of this group share the ability to produce soluble greenish fluorescent siderophores that appear fluorescent under UV illumination (3). These bacteria display a broad potential for adaptation to fluctuating environmental conditions, such as temperature variations, thanks to their highly versatile metabolism and the plasticity of their large genome (4-6). Some species in this group, such as Pseudomonas fluorescens, are commonly associated with plants as saprotrophs, especially in the rhizosphere since their densities and activities are greater than in the surrounding soil (6-9). Some of these populations may have beneficial effects on plant growth and health (10). In contrast, other fluorescent Pseudomonas species are pathogens of humans, animals, and plants, i.e., eukaryotic hosts (11, 12).The type three secretion systems (T3SSs) have been shown to play a determining role in the pathogenicity produced by fluorescent pseudomonads such as P. aeruginosa and P. syringae, pathogens of humans and plants, respectively (11). In these two pathogenic species, T3SS is involved in cell-to-cell contact with the eukaryotic host and in bacterial virulence. Genes encoding the basic structure of th...

Specific Gene Loci of Clinical Pseudomonas putida Isolates

“…The presence of such system has been reported before in strains that belong to the “ P . putida complex” found in blood infections [ 64 ]. In pathogenic bacteria, this needle-like structure secretes effector proteins directly from the bacterial cell into the eukaryotic (host) cell, where they exert a number of effects that help the pathogen to survive and to escape an immune response [ 65 ].…”

“…putida , the only mention in scientific reports is a recent study that described the presence of this kind of structure in blood isolates that were assigned to the “ P . putida complex” [ 64 ].…”

Protective Plant Immune Responses are Elicited by Bacterial Outer Membrane Vesicles

“…A key difference between non-pathogenic commensals and pathogenic bacteria, specifically between P. fluorescens and P. syringae, is the ability of pathogens to overcome plant defenses using the type III secretion system (T3SS) (Deslandes and Rivas, 2012, Feng and Zhou, 2012, Gassmann and Bhattacharjee, 2012, Guo et al, 2009, Mazurier et al, 2015, Büttner and He, 2009. T3SS studies have been instrumental in identifying and defining the complex pathways in plant innate immune responses, but it is understood that many other bacterial secretion pathways also play a role in plantmicrobe interactions.…”

Antibiotic Resistance Patterns of Pseudomonas spp. Isolated from the River Danube

“…It causes a variety of different infections, from easy-to-cure ear infections, serious infections of burn patients, to severe lung infections which lead to major complications in cystic fibrosis patients (Barbier and Wolff, 2010 ; Azzopardi et al, 2014 ). Besides Pseudomonas aeruginosa , other species e.g., Pseudomonas putida or Pseudomonas fluorescens are also a cause for infections in clinical settings (Gilarranz et al, 2013 ; Erol et al, 2014 ; Bhattacharya et al, 2015 ; Mazurier et al, 2015 ).…”