Analysis of the pathogenic potential of nosocomial Pseudomonas putida strains

The Supplementary Material for this article can be found online at: http://journal.frontiersin.org/article/10.3389/fmicb.2015.00871Pseudomonas putida strains are ubiquitous in soil and water but have also been reported as opportunistic human pathogens capable of causing nosocomial infections. In this study we describe the multilocus sequence typing of four P. putida strains (HB13667, HB8234, HB4184, and HB3267) isolated from in-patients at the Besançon Hospital (France). The four isolates (in particular HB3267) were resistant to a number of antibiotics. The pathogenicity and virulence potential of the strains was tested ex vivo and in vivo using different biological models: human tissue culture, mammalian tissues, and insect larvae. Our results showed a significant variability in the ability of the four strains to damage the host; HB13667 did not exhibit any pathogenic traits, HB4184 caused damage only ex vivo in human tissue cultures, and HB8234 had a deleterious effect in tissue culture and in vivo on rat skin, but not in insect larvae. Interestingly, strain HB3267 caused damage in all the model systems studied. The putative evolution of these strains in medical environments is discussed.Work in this study was supported by the ERANET Pathogenomics Program through the ADHERS-Signature Project (reference: BIO2008-04419-E)Peer reviewe

Role of regulated proteolysis in the communication of bacteria with the environment

For bacteria to flourish in different niches, they need to sense signals from the environment and translate these into appropriate responses. Most bacterial signal transduction systems involve proteins that trigger the required response through the modification of gene transcription. These proteins are often produced in an inactive state that prevents their interaction with the RNA polymerase and/or the DNA in the absence of the inducing signal. Among other mechanisms, regulated proteolysis is becoming increasingly recognized as a key process in the modulation of the activity of these signal response proteins. Regulated proteolysis can either produce complete degradation or specific cleavage of the target protein, thus modifying its function. Because proteolysis is a fast process, the modulation of signaling proteins activity by this process allows for an immediate response to a given signal, which facilitates adaptation to the surrounding environment and bacterial survival. Moreover, regulated proteolysis is a fundamental process for the transmission of extracellular signals to the cytosol through the bacterial membranes. By a proteolytic mechanism known as regulated intramembrane proteolysis (RIP) transmembrane proteins are cleaved within the plane of the membrane to liberate a cytosolic domain or protein able to modify gene transcription. This allows the transmission of a signal present on one side of a membrane to the other side where the response is elicited. In this work, we review the role of regulated proteolysis in the bacterial communication with the environment through the modulation of the main bacterial signal transduction systems, namely one- and two-component systems, and alternative σ factors.This work was funded by the FEDER and the Spanish Ministry of Economy with grant BIO2017-83763-P. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI

Unraveling the roles of three uncharacterized extracytoplasmic function sigma (sigmaECF) of the human pathogen Pseudomonas aeruginosa

Resumen del poster presentado en: XIII Reunión del Grupo de Microbiología Molecular de La SEM. Granada, 7-9 septiembre (2022)This work is funded by MCIN/AEI/10.13039/501100011033 Spanish agency with project PID2020-115682GB-I00

Type VI secretion systems in plant-associated bacteria

The type VI secretion system (T6SS) is a bacterial nanomachine used to inject effectors into prokaryotic or eukaryotic cells and is thus involved in both host manipulation and interbacterial competition. The T6SS is widespread among Gram-negative bacteria, mostly within the Proteobacterium Phylum. This secretion system is commonly found in commensal and pathogenic plant-associated bacteria. Phylogenetic analysis of phytobacterial T6SS clusters shows that they are distributed in the five main clades previously described (group 1–5). The even distribution of the system among commensal and pathogenic phytobacteria suggests that the T6SS provides fitness and colonization advantages in planta and that the role of the T6SS is not restricted to virulence. This manuscript reviews the phylogeny and biological roles of the T6SS in plant-associated bacteria, highlighting a remarkable diversity both in terms of mechanism and function.PB is supported by the European Unión through a Marie Curie Individual Fellowship (Ref: 654135 BIOCONT6SS). MAL is supported by the Spanish Ministry of Economy through a Ramon & Cajal grant (RYC2011-08874). AF is supported by a BBSRC grant (BB/N002539/1).Peer Reviewe

Identification of the Pseudomonas aeruginosa sigma-HasI and sigma-HxuI regulons

Resumen del poster presentado en: XXIX Congreso de la Sociedad Española de Microbiología SEM. Microorganismos: un universo en continua evolucion. Burgos, España. 25-28 junio (2023)This work has been funded by the PAIDI-2020 program of Junta de Andalucía/FEDER with project P18-FR-1621 and the MCIN/AEI/10.13039/501100011033 Spanish agency with project PID2020- 115682GB-I00

Sigma ECF-mediated signalling in Pseudomonas aeruginosa: role of the anti-sigma domain (ASD) of the anti-sigma factor in the signalling pathway

Resumen de la comunicación oral presentada en: XIII Reunión del Grupo de Microbiología Molecular de La SEM. Granada, 7-9 septiembre (2022)This work has been funded by the PAIDI-2020 program of Junta de Andalucía/FEDER with project P18-FR-1621

Mechanisms of iron homeostasis in Pseudomonas aeruginosa and emerging therapeutics directed to disrupt this vital process

Pseudomonas aeruginosa is an opportunistic pathogen able to infect any human tissue. One of the reasons for its high adaptability and colonization of host tissues is its capacity of maintaining iron homeostasis through a wide array of iron acquisition and removal mechanisms. Due to their ability to cause life-threatening acute and chronic infections, especially among cystic fibrosis and immunocompromised patients, and their propensity to acquire resistance to many antibiotics, the World Health Organization (WHO) has encouraged the scientific community to find new strategies to eradicate this pathogen. Several recent strategies to battle P. aeruginosa focus on targeting iron homeostasis mechanisms, turning its greatest advantage into an exploitable weak point. In this review, we discuss the different mechanisms used by P. aeruginosa to maintain iron homeostasis and the strategies being developed to fight this pathogen by blocking these mechanisms. Among others, the use of iron chelators and mimics, as well as disruption of siderophore production and uptake, have shown promising results in reducing viability and/or virulence of this pathogen. The so-called ‘Trojan-horse’ strategy taking advantage of the siderophore uptake systems is emerging as an efficient method to improve delivery of antibiotics into the bacterial cells. Moreover, siderophore transporters are considered promising targets for the developing of P. aeruginosa vaccines.Consejería de Transformación Económica, Industria, Conocimiento y Universidades. Junta de Andalucia, Grant/Award Number: P18-FR-1621; Ministerio de Ciencia e Innovación, Gobierno de España. Agencia Estatal de Investigación, Grant/Award Number: PID2020-115682GB- I0

The extracytoplasmic function sigma factor σVreI is active during infection and contributes to phosphate starvation-induced virulence of Pseudomonas aeruginosa

The extracytoplasmic function sigma factor σVreI of the human pathogen Pseudomonas aeruginosa promotes transcription of potential virulence determinants, including secretion systems and secreted proteins. Its activity is modulated by the VreR anti-σ factor that inhibits the binding of σVreI to the RNA polymerase in the absence of a (still unknown) inducing signal. The vreI-vreR genes are expressed under inorganic phosphate (Pi) starvation, a physiological condition often encountered in the host that increases P. aeruginosa pathogenicity. However, whether or not σVreI is active in vivo during infection and contributes to the Pi starvation-induced virulence of this pathogen has not been analyzed yet. Using zebrafish embryos and a human alveolar basal epithelial cell line as P. aeruginosa hosts, we demonstrate in this work that σVreI is active during infection and that lack of σVreI considerably reduces the Pi starvation-induced virulence of this pathogen. Surprisingly, lack of the σVreI inhibitor, the VreR anti-σ factor, also diminishes the virulence of P. aeruginosa. By transcriptomic analyses we show that VreR modulates gene expression not only in a σVreI-dependent but also in a σVreI-independent manner. This includes potential virulence determinants and transcriptional regulators that could be responsible for the reduced virulence of the ΔvreR mutant.We thank W. Koudstaal for critical review of the manuscript, A. van der Sar and T. Verboom (AUMC, Amsterdam) for facilitating the work on zebrafish embryos, F. Madrazo (Instituto de Investigación Sanitaria Valdecilla) for assistance with the confocal fluorescence imaging, and R. Tobes (Era7 Bioinformatics) for the RNA-seq bioinformatics analysis. This work was funded by FEDER and the Spanish Ministry of Economy with grants SAF2015-68873-P and BIO2017-83763-P. JOA was supported by the Spanish Ministry of Economy through a FPI fellowship (BES-2013-066301)

The Pseudomonas putida T6SS is a plant warden against phytopathogens

Bacterial type VI secretion systems (T6SSs) are molecular weapons designed to deliver toxic effectors into prey cells. These nanomachines have an important role in inter-bacterial competition and provide advantages to T6SS active strains in polymicrobial environments. Here we analyze the genome of the biocontrol agent Pseudomonas putida KT2440 and identify three T6SS gene clusters (K1-, K2- and K3-T6SS). Besides, 10 T6SS effector-immunity pairs were found, including putative nucleases and pore-forming colicins. We show that the K1-T6SS is a potent antibacterial device, which secretes a toxic Rhs-type effector Tke2. Remarkably, P. putida eradicates a broad range of bacteria in a K1-T6SS-dependent manner, including resilient phytopathogens, which demonstrates that the T6SS is instrumental to empower P. putida to fight against competitors. Furthermore, we observed a drastically reduced necrosis on the leaves of Nicotiana benthamiana during co-infection with P. putida and Xanthomonas campestris. Such protection is dependent on the activity of the P. putida T6SS. Many routes have been explored to develop biocontrol agents capable of manipulating the microbial composition of the rhizosphere and phyllosphere. Here we unveil a novel mechanism for plant biocontrol, which needs to be considered for the selection of plant wardens whose mission is to prevent phytopathogen infections.We thank Milagros Lopez (IVIA, Spain) for providing X. campestris and P. carotovorum, Martin Buck (Imperial College London, UK) for P. syringae and Ehr Min Lai (Academia Sinica, Taiwan) for A. tumefaciens and the pRL662-gpf. We thank Tom Wood for kindly providing the T6SS scheme shown in Figure 1a. PB is supported by the Spanish Ministry of Economy through Juan de la Cierva grant (JCI-2010-06615), by the Andalusian Knowledge Agency through a Talent Hub grant (TAHUB-010) and by an EMBO short-term fellowship. MAL is supported by the Spanish Ministry of Economy through a Ramon&Cajal grant (RYC2011-08874). AF is supported by a BBSRC grant (BB/N002539/1). LA is supported by a BBSRC grant (BB/N002539/1) and a Marie curie Fellowship (PIIF-GA-2012-328261).Peer Reviewe

Diversity of extracytoplasmic function sigma (σECF) factor-dependent signaling in Pseudomonas

Pseudomonas bacteria are widespread and are found in soil and water, as well as pathogens of both plants and animals. The ability of Pseudomonas to colonize many different environments is facilitated by the multiple signaling systems these bacteria contain that allow Pseudomonas to adapt to changing circumstances by generating specific responses. Among others, signaling through extracytoplasmic function σ (σ) factors is extensively present in Pseudomonas. σ factors trigger expression of functions required under particular conditions in response to specific signals. This manuscript reviews the phylogeny and biological roles of σ factors in Pseudomonas, and highlights the diversity of σ-signaling pathways of this genus in terms of function and activation. We show that Pseudomonas σ factors belong to 16 different phylogenetic groups. Most of them are included within the iron starvation group and are mainly involved in iron acquisition. The second most abundant group is formed by RpoE-like σ factors, which regulate the responses to cell envelope stress. Other groups controlling solvent tolerance, biofilm formation and the response to oxidative stress, among other functions, are present in lower frequency. The role of σ factors in the virulence of Pseudomonas pathogenic species is described.We thank W. Koudstaal for critical review of the manuscript. This work was funded by the European Regional Development Fund and the Spanish Ministry of Economy and Competitiveness (MINECO) with grant BIO2017‐83763‐P.Peer Reviewe