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Microorganisms
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Bacterial Protein Secretion Systems and Toxins: Toolkits for Environmental Fitness
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Bacterial Protein Secretion Systems and Toxins: Toolkits for Environmental Fitness

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Molecular Microbiology and Immunology".

Deadline for manuscript submissions: closed (1 May 2021) | Viewed by 21558

Special Issue Editors

Dr. Dor Salomon

E-Mail Website
Guest Editor
Department of Clinical Microbiology and Immunology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel
Interests: T6SS; vibrio; toxins; bacterial competition; antibacterial; virulence
Prof. Dr. Guido Sessa

E-Mail Website
Guest Editor
Head of the School of Plant Sciences and Food Security, Tel-Aviv University, Tel-Aviv 6997801, Israel
Interests: T3SS; T6SS; effectors; pathogenicity; plant immunity; plant disease; Xanthomonas; Pantoea

Special Issue Information

Dear Colleagues,

Bacteria are social organisms that live in complex communities with other bacteria and predators, or in association with eukaryotic hosts including animals and plants. To manipulate the environment for their benefit, bacteria often employ protein secretion systems that deliver toxins and effector proteins to the extracellular milieu or directly into neighboring cells. Nine major secretion systems have been described, to date, in Gram-negative and Gram-positive bacteria (secretion systems Type 1–9), and they have been shown to play a role in virulence, symbiosis, and interbacterial competition. Understanding the function of secretion systems and identifying their secreted toxins is pivotal to the future development of antibacterial treatment strategies. It may also provide insights into the structure of bacterial communities and be important in areas of human disease, agriculture, and aquaculture. Furthermore, deciphering the mechanisms of action and cellular targets of bacterial toxins can shed light on general cellular processes.

The objective of this Special Issue of Microorganisms is to report novel insights into various aspects of bacterial secretion systems and their toxins, such as the regulatory networks that govern their activation, structure, secretion mechanisms, effector and toxin repertoires, and targets. Original research articles as well as review articles are invited.

Dr. Dor Salomon
Prof. Dr. Guido Sessa
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Microorganisms is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • T3SS
  • T4SS
  • T5SS
  • T6SS
  • T7SS
  • T9SS
  • toxin
  • effector
  • secretion mechanism
  • structure
  • regulation
  • virulence
  • antibacterial

Published Papers (4 papers)

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Review

24 pages, 1327 KiB  
Review
Regulation of the Pseudomonas syringae Type III Secretion System by Host Environment Signals
by Megan R. O’Malley and Jeffrey C. Anderson
Microorganisms 2021, 9(6), 1227; https://doi.org/10.3390/microorganisms9061227 - 5 Jun 2021
Cited by 16 | Viewed by 6111
Abstract
Pseudomonas syringae are Gram-negative, plant pathogenic bacteria that use a type III secretion system (T3SS) to disarm host immune responses and promote bacterial growth within plant tissues. Despite the critical role for type III secretion in promoting virulence, T3SS-encoding genes are not constitutively [...] Read more.
Pseudomonas syringae are Gram-negative, plant pathogenic bacteria that use a type III secretion system (T3SS) to disarm host immune responses and promote bacterial growth within plant tissues. Despite the critical role for type III secretion in promoting virulence, T3SS-encoding genes are not constitutively expressed by P. syringae and must instead be induced during infection. While it has been known for many years that culturing P. syringae in synthetic minimal media can induce the T3SS, relatively little is known about host signals that regulate the deployment of the T3SS during infection. The recent identification of specific plant-derived amino acids and organic acids that induce T3SS-inducing genes in P. syringae has provided new insights into host sensing mechanisms. This review summarizes current knowledge of the regulatory machinery governing T3SS deployment in P. syringae, including master regulators HrpRS and HrpL encoded within the T3SS pathogenicity island, and the environmental factors that modulate the abundance and/or activity of these key regulators. We highlight putative receptors and regulatory networks involved in linking the perception of host signals to the regulation of the core HrpRS–HrpL pathway. Positive and negative regulation of T3SS deployment is also discussed within the context of P. syringae infection, where contributions from distinct host signals and regulatory networks likely enable the fine-tuning of T3SS deployment within host tissues. Last, we propose future research directions necessary to construct a comprehensive model that (a) links the perception of host metabolite signals to T3SS deployment and (b) places these host–pathogen signaling events in the overall context of P. syringae infection. Full article
(This article belongs to the Special Issue Bacterial Protein Secretion Systems and Toxins: Toolkits for Environmental Fitness)
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48 pages, 983 KiB  
Review
What the Wild Things Do: Mechanisms of Plant Host Manipulation by Bacterial Type III-Secreted Effector Proteins
by Karl J. Schreiber, Ilea J. Chau-Ly and Jennifer D. Lewis
Microorganisms 2021, 9(5), 1029; https://doi.org/10.3390/microorganisms9051029 - 11 May 2021
Cited by 33 | Viewed by 5052
Abstract
Phytopathogenic bacteria possess an arsenal of effector proteins that enable them to subvert host recognition and manipulate the host to promote pathogen fitness. The type III secretion system (T3SS) delivers type III-secreted effector proteins (T3SEs) from bacterial pathogens such as Pseudomonas syringae, [...] Read more.
Phytopathogenic bacteria possess an arsenal of effector proteins that enable them to subvert host recognition and manipulate the host to promote pathogen fitness. The type III secretion system (T3SS) delivers type III-secreted effector proteins (T3SEs) from bacterial pathogens such as Pseudomonas syringae, Ralstonia solanacearum, and various Xanthomonas species. These T3SEs interact with and modify a range of intracellular host targets to alter their activity and thereby attenuate host immune signaling. Pathogens have evolved T3SEs with diverse biochemical activities, which can be difficult to predict in the absence of structural data. Interestingly, several T3SEs are activated following injection into the host cell. Here, we review T3SEs with documented enzymatic activities, as well as T3SEs that facilitate virulence-promoting processes either indirectly or through non-enzymatic mechanisms. We discuss the mechanisms by which T3SEs are activated in the cell, as well as how T3SEs modify host targets to promote virulence or trigger immunity. These mechanisms may suggest common enzymatic activities and convergent targets that could be manipulated to protect crop plants from infection. Full article
(This article belongs to the Special Issue Bacterial Protein Secretion Systems and Toxins: Toolkits for Environmental Fitness)
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16 pages, 3889 KiB  
Review
The HrpG/HrpX Regulon of Xanthomonads—An Insight to the Complexity of Regulation of Virulence Traits in Phytopathogenic Bacteria
by Doron Teper, Sheo Shankar Pandey and Nian Wang
Microorganisms 2021, 9(1), 187; https://doi.org/10.3390/microorganisms9010187 - 16 Jan 2021
Cited by 24 | Viewed by 3857
Abstract
Bacteria of the genus Xanthomonas cause a wide variety of economically important diseases in most crops. The virulence of the majority of Xanthomonas spp. is dependent on secretion and translocation of effectors by the type 3 secretion system (T3SS) that is controlled by [...] Read more.
Bacteria of the genus Xanthomonas cause a wide variety of economically important diseases in most crops. The virulence of the majority of Xanthomonas spp. is dependent on secretion and translocation of effectors by the type 3 secretion system (T3SS) that is controlled by two master transcriptional regulators HrpG and HrpX. Since their discovery in the 1990s, the two regulators were the focal point of many studies aiming to decipher the regulatory network that controls pathogenicity in Xanthomonas bacteria. HrpG controls the expression of HrpX, which subsequently controls the expression of T3SS apparatus genes and effectors. The HrpG/HrpX regulon is activated in planta and subjected to tight metabolic and genetic regulation. In this review, we cover the advances made in understanding the regulatory networks that control and are controlled by the HrpG/HrpX regulon and their conservation between different Xanthomonas spp. Full article
(This article belongs to the Special Issue Bacterial Protein Secretion Systems and Toxins: Toolkits for Environmental Fitness)
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9 pages, 1876 KiB  
Review
The Type IX Secretion System: Advances in Structure, Function and Organisation
by Dhana G. Gorasia, Paul D. Veith and Eric C. Reynolds
Microorganisms 2020, 8(8), 1173; https://doi.org/10.3390/microorganisms8081173 - 1 Aug 2020
Cited by 46 | Viewed by 5383
Abstract
The type IX secretion system (T9SS) is specific to the Bacteroidetes phylum. Porphyromonas gingivalis, a keystone pathogen for periodontitis, utilises the T9SS to transport many proteins—including its gingipain virulence factors—across the outer membrane and attach them to the cell surface. Additionally, the [...] Read more.
The type IX secretion system (T9SS) is specific to the Bacteroidetes phylum. Porphyromonas gingivalis, a keystone pathogen for periodontitis, utilises the T9SS to transport many proteins—including its gingipain virulence factors—across the outer membrane and attach them to the cell surface. Additionally, the T9SS is also required for gliding motility in motile organisms, such as Flavobacterium johnsoniae. At least nineteen proteins have been identified as components of the T9SS, including the three transcription regulators, PorX, PorY and SigP. Although the components are known, the overall organisation and the molecular mechanism of how the T9SS operates is largely unknown. This review focusses on the recent advances made in the structure, function, and organisation of the T9SS machinery to provide further insight into this highly novel secretion system. Full article
(This article belongs to the Special Issue Bacterial Protein Secretion Systems and Toxins: Toolkits for Environmental Fitness)
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