The Type VI Secretion System of Pseudomonas aeruginosa: a gun loaded with antimicrobial bullets

Pseudomonas aeruginosa is an opportunistic pathogen that can cause severe respiratory infections in people who are immunocompromised. P. aeruginosa possesses the Type VI Secretion System (T6SS), a bacterial weapon that injects effectors into neighbouring prokaryotes and eukaryotes. The T6SS is crucial for bacterial warfare, allowing P. aeruginosa to kill its competitors, which promotes its dominance in mixed microbial environments. P. aeruginosa has three T6SSs, H1/2/3-T6SS, these are structural homologs but deliver unique effectors. Effectors are delivered via the secreted component, a Hcp tube topped with a VgrG and PAAR spike. Only the first three identified effectors are delivered by Hcp1. Since then, there has been a bias in identification of VgrG or PAAR delivered effectors, mostly as these are encoded next to the spike proteins. Some P. aeruginosa effectors not only kill bacteria but have a dual role in pathogenesis. Our aim was to identify a comprehensive set of Hcp-delivered effectors for all three systems. Using Hcp1/2/3, systematic pull-down screens were performed to identify novel interaction partners. After confirming interaction, antibacterial toxicity was evaluated, identifying new Hcp delivered T6SS effectors for Hcp2 and Hcp3, which are toxic in the bacterial cytoplasm. These new anti-bacterial effectors may kill bacteria in novel ways, which could lead to novel antibiotics. Additionally, a toxin fusion proved too large for secretion and blocked the T6SS, revealing a Hcp-delivered effector size limit. Future work will focus on fully characterising these new toxins, as well as to look into the potential eukaryotic role of other interaction partners.

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Transcriptional Response of Mucoid Pseudomonas aeruginosa to Human Respiratory Mucus

mBio ◽

10.1128/mbio.00410-12 ◽

2012 ◽

Vol 3 (6) ◽

Cited By ~ 13

Author(s):

V. Cattoir ◽

G. Narasimhan ◽

D. Skurnik ◽

H. Aschard ◽

D. Roux ◽

...

Keyword(s):

Cystic Fibrosis ◽

Pseudomonas Aeruginosa ◽

Opportunistic Pathogen ◽

Secretion System ◽

Type Vi Secretion System ◽

Transcript Levels ◽

Content Type ◽

Type Vi Secretion ◽

Small Regulatory Rnas ◽

Regulatory Rnas

ABSTRACTAdaptation of bacterial pathogens to a host can lead to the selection and accumulation of specific mutations in their genomes with profound effects on the overall physiology and virulence of the organisms. The opportunistic pathogenPseudomonas aeruginosais capable of colonizing the respiratory tract of individuals with cystic fibrosis (CF), where it undergoes evolution to optimize survival as a persistent chronic human colonizer. The transcriptome of a host-adapted, alginate-overproducing isolate from a CF patient was determined following growth of the bacteria in the presence of human respiratory mucus. This stable mucoid strain responded to a number of regulatory inputs from the mucus, resulting in an unexpected repression of alginate production. Mucus in the medium also induced the production of catalases and additional peroxide-detoxifying enzymes and caused reorganization of pathways of energy generation. A specific antibacterial type VI secretion system was also induced in mucus-grown cells. Finally, a group of small regulatory RNAs was identified and a fraction of these were mucus regulated. This report provides a snapshot of responses in a pathogen adapted to a human host through assimilation of regulatory signals from tissues, optimizing its long-term survival potential.IMPORTANCEThe basis for chronic colonization of patients with cystic fibrosis (CF) by the opportunistic pathogenPseudomonas aeruginosacontinues to represent a challenging problem for basic scientists and clinicians. In this study, the host-adapted, alginate-overproducingPseudomonas aeruginosa2192 strain was used to assess the changes in its transcript levels following growth in respiratory CF mucus. Several significant and unexpected discoveries were made: (i) although the alginate overproduction in strain 2192 was caused by a stable mutation, a mucus-derived signal caused reduction in the transcript levels of alginate biosynthetic genes; (ii) mucus activated the expression of the type VI secretion system, a mechanism for killing of other bacteria in a mixed population; (iii) expression of a number of genes involved in respiration was altered; and (iv) several small regulatory RNAs were identified, some being mucus regulated. This work highlights the strong influence of the host environment in shaping bacterial survival strategies.

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YbeY controls the type III and type VI secretion systems and biofilm formation through RetS in Pseudomonas aeruginosa

Applied and Environmental Microbiology ◽

10.1128/aem.02171-20 ◽

2020 ◽

Author(s):

Yushan Xia ◽

Congjuan Xu ◽

Dan Wang ◽

Yuding Weng ◽

Yongxin Jin ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Type Iii Secretion ◽

Biofilm Formation ◽

Small Rnas ◽

Type Iii Secretion System ◽

Secretion System ◽

Type Vi Secretion System ◽

Chronic Infections ◽

Type Iii ◽

Type Vi Secretion

YbeY is a highly conserved RNase in bacteria and plays essential roles in the maturation of 16S rRNA, regulation of small RNAs (sRNAs) and bacterial responses to environmental stresses. Previously, we verified the role of YbeY in rRNA processing and ribosome maturation in Pseudomonas aeruginosa and demonstrated YbeY-mediated regulation of rpoS through a sRNA ReaL. In this study, we demonstrate that mutation of the ybeY gene results in upregulation of the type III secretion system (T3SS) genes as well as downregulation of the type VI secretion system (T6SS) genes and reduction of biofilm formation. By examining the expression of the known sRNAs in P. aeruginosa, we found that mutation of the ybeY gene leads to downregulation of the small RNAs RsmY/Z that control the T3SS, the T6SS and biofilm formation. Further studies revealed that the reduced levels of RsmY/Z are due to upregulation of retS. Taken together, our results reveal the pleiotropic functions of YbeY and provide detailed mechanisms of YbeY-mediated regulation in P. aeruginosa. IMPORTANCE Pseudomonas aeruginosa causes a variety of acute and chronic infections in humans. The type III secretion system (T3SS) plays an important role in acute infection and the type VI secretion system (T6SS) and biofilm formation are associated with chronic infections. Understanding of the mechanisms that control the virulence determinants involved in acute and chronic infections will provide clues for the development of effective treatment strategies. Our results reveal a novel RNase mediated regulation on the T3SS, T6SS and biofilm formation in P. aeruginosa.

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ClpV3 of the H3-Type VI Secretion System (H3-T6SS) Affects Multiple Virulence Factors in Pseudomonas aeruginosa

Frontiers in Microbiology ◽

10.3389/fmicb.2020.01096 ◽

2020 ◽

Vol 11 ◽

Cited By ~ 1

Author(s):

Yanqi Li ◽

Lin Chen ◽

Pansong Zhang ◽

Anjali Y. Bhagirath ◽

Kangmin Duan

Keyword(s):

Pseudomonas Aeruginosa ◽

Virulence Factors ◽

Secretion System ◽

Type Vi Secretion System ◽

Type Vi Secretion

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Type VI Secretion System Dynamics Reveals a Novel Secretion Mechanism in Pseudomonas aeruginosa

Journal of Bacteriology ◽

10.1128/jb.00744-17 ◽

2018 ◽

Vol 200 (11) ◽

Cited By ~ 8

Author(s):

Jacqueline Corbitt ◽

Jun Seok Yeo ◽

C. Ian Davis ◽

Michele LeRoux ◽

Paul A. Wiggins

Keyword(s):

Pseudomonas Aeruginosa ◽

Vibrio Cholerae ◽

Conformational Change ◽

Secretion System ◽

Force Generation ◽

Type Vi Secretion System ◽

Content Type ◽

Evolutionary Diversification ◽

Type Vi Secretion ◽

Generation Mechanisms

ABSTRACT The type VI secretion system (T6SS) inhibits the growth of neighboring bacterial cells through a contact-mediated mechanism. Here, we describe a detailed characterization of the protein localization dynamics in the Pseudomonas aeruginosa T6SS. It has been proposed that the type VI secretion process is driven by a conformational-change-induced contraction of the T6SS sheath. However, although the contraction of an optically resolvable TssBC sheath and the subsequent localization of ClpV are observed in Vibrio cholerae , coordinated assembly and disassembly of TssB and ClpV are observed without TssB contraction in P. aeruginosa . These dynamics are inconsistent with the proposed contraction sheath model. Motivated by the phenomenon of dynamic instability, we propose a new model in which ATP hydrolysis, rather than conformational change, generates the force for secretion. IMPORTANCE The type VI secretion system (T6SS) is widely conserved among Gram-negative bacteria and is a central determinant of bacterial fitness in polymicrobial communities. The secretion system targets bacteria and secretes effectors that inhibit the growth of neighboring cells, using a contact-mediated-delivery system. Despite significant homology to the previously characterized Vibrio cholerae T6SS, our analysis reveals that effector secretion is driven by a distinct force generation mechanism in Pseudomonas aeruginosa . The presence of two distinct force generation mechanisms in T6SS represents an example of the evolutionary diversification of force generation mechanisms.

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A family of Type VI secretion system effector proteins that form ion-selective pores

Nature Communications ◽

10.1038/s41467-019-13439-0 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 18

Author(s):

Giuseppina Mariano ◽

Katharina Trunk ◽

David J. Williams ◽

Laura Monlezun ◽

Henrik Strahl ◽

...

Keyword(s):

Opportunistic Pathogen ◽

Effector Proteins ◽

Type Vi Secretion System ◽

Secretion Systems ◽

New Family ◽

Type Vi Secretion ◽

Genes Encoding ◽

Outer Membrane Permeability ◽

Bacterial Effectors

AbstractType VI secretion systems (T6SSs) are nanomachines widely used by bacteria to deliver toxic effector proteins directly into neighbouring cells. However, the modes of action of many effectors remain unknown. Here we report that Ssp6, an anti-bacterial effector delivered by a T6SS of the opportunistic pathogen Serratia marcescens, is a toxin that forms ion-selective pores. Ssp6 inhibits bacterial growth by causing depolarisation of the inner membrane in intoxicated cells, together with increased outer membrane permeability. Reconstruction of Ssp6 activity in vitro demonstrates that it forms cation-selective pores. A survey of bacterial genomes reveals that genes encoding Ssp6-like effectors are widespread in Enterobacteriaceae and often linked with T6SS genes. We conclude that Ssp6 and similar proteins represent a new family of T6SS-delivered anti-bacterial effectors.

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