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Microorganisms
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Microbial Functional Amyloids
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Microbial Functional Amyloids

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

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 14117

Special Issue Editor

Prof. Dr. Meytal Landau

E-Mail Website
Guest Editor
Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
Interests: amyloids; functional fibrils; antimicrobials; antivirulence; structural biology; X-ray crystallography; electron microscopy; biophysics; drug discovery; infectious diseases; aggregation diseases

Special Issue Information

Dear Colleagues,

Microbial functional amyloids are proteins that self-assemble into fibrous structures that play roles mostly as virulence determinants, for example, in biofilm structuring, adhesion, and attacking host immune cells and competing bacteria. Microbial amyloids therefore offer promising targets for the design of antivirulence drugs. Due to their unique supramolecular structures, some microbial amyloids are considered templates for durable biomaterials. Microbial amyloids can potentially be regarded as transmissible agents, just like prions, affecting human aggregation diseases. Overall, they present attractive templates for numerous potential medical and technological applications. The biofilm-associated enterobacterial curli is the most extensively studied microbial amyloid system; yet, it is becoming clear that extensive differences exist between amyloids from different microbes, showing no sequence or structural conservation. One such example is the PSM peptide family secreted by the pathogenic Staphylococcus aureus bacterium, showing diverse structures of fibrils encoding mostly toxic activities against human and bacterial cells. The identification of numerous additional amyloids from bacteria, fungi, and viruses calls for comprehensive studies of each individual system. The objective of this Special Issue of Microorganisms is to present some of the latest insights into microbial amyloid functions, assembly mechanisms, structures, interactions, mechanism of action, and inhibition. Original research articles as well as review articles are invited.

Prof. Dr. Meytal Landau
Guest Editor

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.

Published Papers (5 papers)

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Editorial

Jump to: Research, Review

2 pages, 182 KiB  
Editorial
Beyond One-Trick Ponies: The Multifunctional Marvels of Microbial Functional Amyloids
by Meytal Landau
Microorganisms 2023, 11(5), 1201; https://doi.org/10.3390/microorganisms11051201 - 4 May 2023
Cited by 2 | Viewed by 856
Abstract
Various organisms, including bacteria, protists, fungi, plants, and animals, secrete proteins and peptides that self-assemble into ordered amyloid fibrils that perform different physiological functions [...] Full article
(This article belongs to the Special Issue Microbial Functional Amyloids)

Research

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12 pages, 2217 KiB  
Article
Fibrilar Polymorphism of the Bacterial Extracellular Matrix Protein TasA
by Mnar Ghrayeb, Shahar Hayet, Neta Lester-Zer, Yael Levi-Kalisman and Liraz Chai
Microorganisms 2021, 9(3), 529; https://doi.org/10.3390/microorganisms9030529 - 4 Mar 2021
Cited by 8 | Viewed by 2330
Abstract
Functional amyloid proteins often appear as fibers in extracellular matrices of microbial soft colonies. In contrast to disease-related amyloid structures, they serve a functional goal that benefits the organism that secretes them, which is the reason for the title “functional”. Biofilms are a [...] Read more.
Functional amyloid proteins often appear as fibers in extracellular matrices of microbial soft colonies. In contrast to disease-related amyloid structures, they serve a functional goal that benefits the organism that secretes them, which is the reason for the title “functional”. Biofilms are a specific example of a microbial community in which functional amyloid fibers play a role. Functional amyloid proteins contribute to the mechanical stability of biofilms and mediate the adhesion of the cells to themselves as well as to surfaces. Recently, it has been shown that functional amyloid proteins also play a regulatory role in biofilm development. TasA is the major proteinaceous fibrilar component of the extracellular matrix of biofilms made of the soil bacterium and Gram-positive Bacillus subtilis. We have previously shown, as later corroborated by others, that in acidic solutions, TasA forms compact aggregates that are composed of tangled fibers. Here, we show that in a neutral pH and above a certain TasA concentration, the fibers of TasA are elongated and straight and that they bundle up in highly concentrated salt solutions. TasA fibers resemble the canonic amyloid morphology; however, these fibers also bear an interesting nm-scale periodicity along the fiber axis. At the molecular level, TasA fibers contain a twisted β-sheet structure, as indicated by circular dichroism measurements. Our study shows that the morphology of TasA fibers depends on the environmental conditions. Different fibrilar morphologies may be related with different functional roles in biofilms, ranging from granting biofilms with a mechanical support to acting as antibiotic agents. Full article
(This article belongs to the Special Issue Microbial Functional Amyloids)
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17 pages, 2270 KiB  
Article
Modulating Kinetics of the Amyloid-Like Aggregation of S. aureus Phenol-Soluble Modulins by Changes in pH
by Masihuz Zaman and Maria Andreasen
Microorganisms 2021, 9(1), 117; https://doi.org/10.3390/microorganisms9010117 - 7 Jan 2021
Cited by 13 | Viewed by 2796
Abstract
The pathogen Staphylococcus aureus is recognized as one of the most frequent causes of biofilm-associated infections. The recently identified phenol-soluble modulin (PSM) peptides act as the key molecular effectors of staphylococcal biofilm maturation and promote the formation of an aggregated fibril structure. The [...] Read more.
The pathogen Staphylococcus aureus is recognized as one of the most frequent causes of biofilm-associated infections. The recently identified phenol-soluble modulin (PSM) peptides act as the key molecular effectors of staphylococcal biofilm maturation and promote the formation of an aggregated fibril structure. The aim of this study was to evaluate the effect of various pH values on the formation of functional amyloids of individual PSM peptides. Here, we combined a range of biophysical, chemical kinetics and microscopic techniques to address the structure and aggregation mechanism of individual PSMs under different conditions. We established that there is a pH-induced switch in PSM aggregation kinetics. Different lag times and growth of fibrils were observed, which indicates that there was no clear correlation between the rates of fibril elongation among different PSMs. This finding confirms that pH can modulate the aggregation properties of these peptides and suggest a deeper understanding of the formation of aggregates, which represents an important basis for strategies to interfere and might help in reducing the risk of biofilm-related infections. Full article
(This article belongs to the Special Issue Microbial Functional Amyloids)
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Review

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20 pages, 3399 KiB  
Review
Multifunctional Amyloids in the Biology of Gram-Positive Bacteria
by Ana Álvarez-Mena, Jesús Cámara-Almirón, Antonio de Vicente and Diego Romero
Microorganisms 2020, 8(12), 2020; https://doi.org/10.3390/microorganisms8122020 - 17 Dec 2020
Cited by 9 | Viewed by 3262
Abstract
Since they were discovered, amyloids have proven to be versatile proteins able to participate in a variety of cellular functions across all kingdoms of life. This multitask trait seems to reside in their ability to coexist as monomers, aggregates or fibrillar entities, with [...] Read more.
Since they were discovered, amyloids have proven to be versatile proteins able to participate in a variety of cellular functions across all kingdoms of life. This multitask trait seems to reside in their ability to coexist as monomers, aggregates or fibrillar entities, with morphological and biochemical peculiarities. It is precisely this common molecular behaviour that allows amyloids to cross react with one another, triggering heterologous aggregation. In bacteria, many of these functional amyloids are devoted to the assembly of biofilms by organizing the matrix scaffold that keeps cells together. However, consistent with their notion of multifunctional proteins, functional amyloids participate in other biological roles within the same organisms, and emerging unprecedented functions are being discovered. In this review, we focus on functional amyloids reported in gram-positive bacteria, which are diverse in their assembly mechanisms and remarkably specific in their biological functions that they perform. Finally, we consider cross-seeding between functional amyloids as an emerging theme in interspecies interactions that contributes to the diversification of bacterial biology. Full article
(This article belongs to the Special Issue Microbial Functional Amyloids)
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13 pages, 2029 KiB  
Review
Functional Amyloids Are the Rule Rather Than the Exception in Cellular Biology
by Anthony Balistreri, Emily Goetzler and Matthew Chapman
Microorganisms 2020, 8(12), 1951; https://doi.org/10.3390/microorganisms8121951 - 9 Dec 2020
Cited by 36 | Viewed by 4121
Abstract
Amyloids are a class of protein aggregates that have been historically characterized by their relationship with human disease. Indeed, amyloids can be the result of misfolded proteins that self-associate to form insoluble, extracellular plaques in diseased tissue. For the first 150 years of [...] Read more.
Amyloids are a class of protein aggregates that have been historically characterized by their relationship with human disease. Indeed, amyloids can be the result of misfolded proteins that self-associate to form insoluble, extracellular plaques in diseased tissue. For the first 150 years of their study, the pathogen-first definition of amyloids was sufficient. However, new observations of amyloids foster an appreciation for non-pathological roles for amyloids in cellular systems. There is now evidence from all domains of life that amyloids can be non-pathogenic and functional, and that their formation can be the result of purposeful and controlled cellular processes. So-called functional amyloids fulfill an assortment of biological functions including acting as structural scaffolds, regulatory mechanisms, and storage mechanisms. The conceptual convergence of amyloids serving a functional role has been repeatedly confirmed by discoveries of additional functional amyloids. With dozens already known, and with the vigorous rate of discovery, the biology of amyloids is robustly represented by non-pathogenic amyloids. Full article
(This article belongs to the Special Issue Microbial Functional Amyloids)
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