1
|
Arbulu S, Kjos M. Revisiting the Multifaceted Roles of Bacteriocins : The Multifaceted Roles of Bacteriocins. MICROBIAL ECOLOGY 2024; 87:41. [PMID: 38351266 PMCID: PMC10864542 DOI: 10.1007/s00248-024-02357-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Accepted: 02/01/2024] [Indexed: 02/16/2024]
Abstract
Bacteriocins are gene-encoded antimicrobial peptides produced by bacteria. These peptides are heterogeneous in terms of structure, antimicrobial activities, biosynthetic clusters, and regulatory mechanisms. Bacteriocins are widespread in nature and may contribute to microbial diversity due to their capacity to target specific bacteria. Primarily studied as food preservatives and therapeutic agents, their function in natural settings is however less known. This review emphasizes the ecological significance of bacteriocins as multifunctional peptides by exploring bacteriocin distribution, mobility, and their impact on bacterial population dynamics and biofilms.
Collapse
Affiliation(s)
- Sara Arbulu
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway.
| | - Morten Kjos
- Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway.
| |
Collapse
|
2
|
Paškevičius Š, Gleba Y, Ražanskienė A. Stenocins: novel modular bacteriocins from opportunistic pathogen Stenotrophomonas maltophilia. J Biotechnol 2022; 351:9-12. [DOI: 10.1016/j.jbiotec.2022.04.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Revised: 04/11/2022] [Accepted: 04/12/2022] [Indexed: 10/18/2022]
|
3
|
Antimicrobial Weapons of Pseudomonas aeruginosa. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1386:223-256. [DOI: 10.1007/978-3-031-08491-1_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
4
|
The Biology of Colicin M and Its Orthologs. Antibiotics (Basel) 2021; 10:antibiotics10091109. [PMID: 34572691 PMCID: PMC8469651 DOI: 10.3390/antibiotics10091109] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 09/06/2021] [Accepted: 09/09/2021] [Indexed: 12/24/2022] Open
Abstract
The misuse of antibiotics during the last decades led to the emergence of multidrug resistant pathogenic bacteria. This phenomenon constitutes a major public health issue. Consequently, the discovery of new antibacterials in the short term is crucial. Colicins, due to their antibacterial properties, thus constitute good candidates. These toxin proteins, produced by E. coli to kill enteric relative competitors, exhibit cytotoxicity through ionophoric activity or essential macromolecule degradation. Among the 25 colicin types known to date, colicin M (ColM) is the only one colicin interfering with peptidoglycan biosynthesis. Accordingly, ColM develops its lethal activity in E. coli periplasm by hydrolyzing the last peptidoglycan precursor, lipid II, into two dead-end products, thereby leading to cell lysis. Since the discovery of its unusual mode of action, several ColM orthologs have also been identified based on sequence alignments; all of the characterized ColM-like proteins display the same enzymatic activity of lipid II degradation and narrow antibacterial spectra. This publication aims at being an exhaustive review of the current knowledge on this new family of antibacterial enzymes as well as on their potential use as food preservatives or therapeutic agents.
Collapse
|
5
|
Carim S, Azadeh AL, Kazakov AE, Price MN, Walian PJ, Lui LM, Nielsen TN, Chakraborty R, Deutschbauer AM, Mutalik VK, Arkin AP. Systematic discovery of pseudomonad genetic factors involved in sensitivity to tailocins. THE ISME JOURNAL 2021; 15:2289-2305. [PMID: 33649553 PMCID: PMC8319346 DOI: 10.1038/s41396-021-00921-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 01/14/2021] [Accepted: 02/01/2021] [Indexed: 12/13/2022]
Abstract
Tailocins are bactericidal protein complexes produced by a wide variety of bacteria that kill closely related strains and may play a role in microbial community structure. Thanks to their high specificity, tailocins have been proposed as precision antibacterial agents for therapeutic applications. Compared to tailed phages, with whom they share an evolutionary and morphological relationship, bacterially produced tailocins kill their host upon production but producing strains display resistance to self-intoxication. Though lipopolysaccharide (LPS) has been shown to act as a receptor for tailocins, the breadth of factors involved in tailocin sensitivity, and the mechanisms behind resistance to self-intoxication, remain unclear. Here, we employed genome-wide screens in four non-model pseudomonads to identify mutants with altered fitness in the presence of tailocins produced by closely related pseudomonads. Our mutant screens identified O-antigen composition and display as most important in defining sensitivity to our tailocins. In addition, the screens suggest LPS thinning as a mechanism by which resistant strains can become more sensitive to tailocins. We validate many of these novel findings, and extend these observations of tailocin sensitivity to 130 genome-sequenced pseudomonads. This work offers insights into tailocin-bacteria interactions, informing the potential use of tailocins in microbiome manipulation and antibacterial therapy.
Collapse
Affiliation(s)
- Sean Carim
- Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA
| | - Ashley L Azadeh
- Innovative Genomics Institute, University of California, Berkeley, CA, USA
| | - Alexey E Kazakov
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Morgan N Price
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Peter J Walian
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Lauren M Lui
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Torben N Nielsen
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Romy Chakraborty
- Climate and Ecosystem Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Adam M Deutschbauer
- Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Vivek K Mutalik
- Innovative Genomics Institute, University of California, Berkeley, CA, USA.
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
| | - Adam P Arkin
- Innovative Genomics Institute, University of California, Berkeley, CA, USA.
- Environmental Genomics and Systems Biology, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
- Department of Bioengineering, University of California, Berkeley, CA, USA.
| |
Collapse
|
6
|
Sitter TL, Vaughan AL, Schoof M, Jackson SA, Glare TR, Cox MP, Fineran PC, Gardner PP, Hurst MRH. Evolution of virulence in a novel family of transmissible mega-plasmids. Environ Microbiol 2021; 23:5289-5304. [PMID: 33989447 DOI: 10.1111/1462-2920.15595] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 05/08/2021] [Accepted: 05/10/2021] [Indexed: 11/27/2022]
Abstract
Some Serratia entomophila isolates have been successfully exploited in biopesticides due to their ability to cause amber disease in larvae of the Aotearoa (New Zealand) endemic pasture pest, Costelytra giveni. Anti-feeding prophage and ABC toxin complex virulence determinants are encoded by a 153-kb single-copy conjugative plasmid (pADAP; amber disease-associated plasmid). Despite growing understanding of the S. entomophila pADAP model plasmid, little is known about the wider plasmid family. Here, we sequence and analyse mega-plasmids from 50 Serratia isolates that induce variable disease phenotypes in the C. giveni insect host. Mega-plasmids are highly conserved within S. entomophila, but show considerable divergence in Serratia proteamaculans with other variants in S. liquefaciens and S. marcescens, likely reflecting niche adaption. In this study to reconstruct ancestral relationships for a complex mega-plasmid system, strong co-evolution between Serratia species and their plasmids were found. We identify 12 distinct mega-plasmid genotypes, all sharing a conserved gene backbone, but encoding highly variable accessory regions including virulence factors, secondary metabolite biosynthesis, Nitrogen fixation genes and toxin-antitoxin systems. We show that the variable pathogenicity of Serratia isolates is largely caused by presence/absence of virulence clusters on the mega-plasmids, but notably, is augmented by external chromosomally encoded factors.
Collapse
Affiliation(s)
- Thomas L Sitter
- Forage Science, AgResearch, Lincoln Research Centre, Christchurch, New Zealand.,Bio-Protection Research Centre, Lincoln, New Zealand
| | - Amy L Vaughan
- Forage Science, AgResearch, Lincoln Research Centre, Christchurch, New Zealand.,Bio-Protection Research Centre, Lincoln, New Zealand
| | - Marion Schoof
- Forage Science, AgResearch, Lincoln Research Centre, Christchurch, New Zealand.,Bio-Protection Research Centre, Lincoln, New Zealand
| | - Simon A Jackson
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | | | - Murray P Cox
- Bio-Protection Research Centre, Lincoln, New Zealand.,Statistics and Bioinformatics Group, School of Fundamental Sciences, Massey University, Palmerston North, New Zealand
| | - Peter C Fineran
- Bio-Protection Research Centre, Lincoln, New Zealand.,Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Paul P Gardner
- Bio-Protection Research Centre, Lincoln, New Zealand.,Department of Biochemistry, University of Otago, Dunedin, New Zealand
| | - Mark R H Hurst
- Forage Science, AgResearch, Lincoln Research Centre, Christchurch, New Zealand.,Bio-Protection Research Centre, Lincoln, New Zealand
| |
Collapse
|
7
|
Shushan A, Kosloff M. Structural design principles for specific ultra-high affinity interactions between colicins/pyocins and immunity proteins. Sci Rep 2021; 11:3789. [PMID: 33589691 PMCID: PMC7884437 DOI: 10.1038/s41598-021-83265-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 01/28/2021] [Indexed: 12/13/2022] Open
Abstract
The interactions of the antibiotic proteins colicins/pyocins with immunity proteins is a seminal model system for studying protein–protein interactions and specificity. Yet, a precise and quantitative determination of which structural elements and residues determine their binding affinity and specificity is still lacking. Here, we used comparative structure-based energy calculations to map residues that substantially contribute to interactions across native and engineered complexes of colicins/pyocins and immunity proteins. We show that the immunity protein α1–α2 motif is a unique structurally-dissimilar element that restricts interaction specificity towards all colicins/pyocins, in both engineered and native complexes. This motif combines with a diverse and extensive array of electrostatic/polar interactions that enable the exquisite specificity that characterizes these interactions while achieving ultra-high affinity. Surprisingly, the divergence of these contributing colicin residues is reciprocal to residue conservation in immunity proteins. The structurally-dissimilar immunity protein α1–α2 motif is recognized by divergent colicins similarly, while the conserved immunity protein α3 helix interacts with diverse colicin residues. Electrostatics thus plays a key role in setting interaction specificity across all colicins and immunity proteins. Our analysis and resulting residue-level maps illuminate the molecular basis for these protein–protein interactions, with implications for drug development and rational engineering of these interfaces.
Collapse
Affiliation(s)
- Avital Shushan
- The Department of Human Biology, Faculty of Natural Sciences, University of Haifa, 199 Aba Khoushy Ave., Mt. Carmel, 3498838, Haifa, Israel
| | - Mickey Kosloff
- The Department of Human Biology, Faculty of Natural Sciences, University of Haifa, 199 Aba Khoushy Ave., Mt. Carmel, 3498838, Haifa, Israel.
| |
Collapse
|
8
|
Impact of FiuA Outer Membrane Receptor Polymorphism on the Resistance of Pseudomonas aeruginosa toward Peptidoglycan Lipid II-Targeting PaeM Pyocins. J Bacteriol 2019; 201:JB.00164-19. [PMID: 30988031 DOI: 10.1128/jb.00164-19] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2019] [Accepted: 04/04/2019] [Indexed: 12/29/2022] Open
Abstract
Certain Pseudomonas aeruginosa strains produce a homolog of colicin M, namely, PaeM, that specifically inhibits peptidoglycan biosynthesis of susceptible P. aeruginosa strains by hydrolyzing the lipid II intermediate precursor. Two variants of this pyocin were identified whose sequences mainly differed in the N-terminal protein moiety, i.e., the region involved in the binding to the FiuA outer membrane receptor and translocation into the periplasm. The antibacterial activity of these two variants, PaeM1 and PaeM2, was tested against various P. aeruginosa strains comprising reference strains PAO1 and PA14, PaeM-producing strains, and 60 clinical isolates. Seven of these strains, including PAO1, were susceptible to only one variant (2 to PaeM1 and 5 to PaeM2), and 11 were affected by both. The remaining strains, including PA14 and four PaeM1 producers, were resistant to both variants. The differences in the antibacterial spectra of the two PaeM homologs prompted us to investigate the molecular determinants allowing their internalization into P. aeruginosa cells, taking the PAO1 strain that is susceptible to PaeM2 but resistant to PaeM1 as the indicator strain. Heterologous expression of fiuA gene orthologs from different strains into PAO1, site-directed mutagenesis experiments, and construction of PaeM chimeric proteins provided evidence that the cell susceptibility and discrimination differences between the PaeM variants resulted from a polymorphism of both the pyocin and the outer membrane receptor FiuA. Moreover, we found that a third component, TonB1, a protein involved in iron transport in P. aeruginosa, working together with FiuA and the ExbB/ExbD complex, was directly implicated in this discrimination.IMPORTANCE Bacterial antibiotic resistance constitutes a threat to human health, imposing the need for identification of new targets and development of new strategies to fight multiresistant pathogens. Bacteriocins and other weapons that bacteria have themselves developed to kill competitors are therefore of great interest and a valuable source of inspiration for us. Attention was paid here to two variants of a colicin M homolog (PaeM) produced by certain strains of P. aeruginosa that inhibit the growth of their congeners by blocking cell wall peptidoglycan synthesis. Molecular determinants allowing recognition of these pyocins by the outer membrane receptor FiuA were identified, and a receptor polymorphism affecting the susceptibility of P. aeruginosa clinical strains was highlighted, providing new insights into the potential use of these pyocins as an alternative to antibiotics.
Collapse
|
9
|
Ghequire MGK, De Mot R. LlpB represents a second subclass of lectin-like bacteriocins. Microb Biotechnol 2019; 12:567-573. [PMID: 30702207 PMCID: PMC6465234 DOI: 10.1111/1751-7915.13373] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 01/14/2019] [Accepted: 01/15/2019] [Indexed: 12/11/2022] Open
Abstract
Bacteriocins are secreted bacterial proteins that selectively kill related strains. Lectin-like bacteriocins are atypical bacteriocins not requiring a cognate immunity factor and have been primarily studied in Pseudomonas. These so-called LlpAs are composed of a tandem of B-lectin domains. One domain interacts with d-rhamnose residues in the common polysaccharide antigen of Pseudomonas lipopolysaccharide (LPS). The other lectin domain is crucial for interference with the outer membrane protein assembly machinery by interacting with surface-exposed loops of its central component BamA. Via genome mining, we identified a second subclass of Pseudomonas lectin-like proteins, termed LlpB, consisting of a single B-lectin domain. We show that these proteins also display bactericidal activity. Among LlpB-resistant transposon mutants of an LlpB-susceptible Pseudomonas strain, a major subset was hit in an acyltransferase gene, predicted to be involved in LPS core modification, hereby suggesting that LlpBs equally attach to LPS for surface anchoring. This indicates that LPS binding and target strain specificity are condensed in a single B-lectin domain. The identification of this second subclass of lectin-like bacteriocins further expands the toolbox of antibacterial warfare deployed by bacteria and holds potential for their integration in biotechnological applications.
Collapse
Affiliation(s)
- Maarten G. K. Ghequire
- Centre of Microbial and Plant GeneticsKU LeuvenKasteelpark Arenberg 20 bus 24603001HeverleeBelgium
| | - René De Mot
- Centre of Microbial and Plant GeneticsKU LeuvenKasteelpark Arenberg 20 bus 24603001HeverleeBelgium
| |
Collapse
|
10
|
Ghequire MGK, Öztürk B, De Mot R. Lectin-Like Bacteriocins. Front Microbiol 2018; 9:2706. [PMID: 30483232 PMCID: PMC6240691 DOI: 10.3389/fmicb.2018.02706] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 10/23/2018] [Indexed: 12/22/2022] Open
Abstract
Bacteria produce a diverse array of antagonistic compounds to restrict growth of microbial rivals. Contributing to this warfare are bacteriocins: secreted antibacterial peptides, proteins and multi-protein complexes. These compounds typically eliminate competitors closely related to the producer. Lectin-like bacteriocins (LlpAs) constitute a distinct class of such proteins, produced by Pseudomonas as well as some other proteobacterial genera. LlpAs share a common architecture consisting of two B-lectin domains, followed by a short carboxy-terminal extension. Two surface-exposed moieties on susceptible Pseudomonas cells are targeted by the respective lectin modules. The carboxy-terminal domain binds D-rhamnose residues present in the lipopolysaccharide layer, whereas the amino-terminal domain interacts with a polymorphic external loop of the outer-membrane protein insertase BamA, hence determining selectivity. The absence of a toxin-immunity module as found in modular bacteriocins and other polymorphic toxin systems, hints toward a novel mode of killing initiated at the cellular surface, not requiring bacteriocin import. Despite significant progress in understanding the function of LlpAs, outstanding questions include the secretion machinery recruited by lectin-like bacteriocins for their release, as well as a better understanding of the environmental signals initiating their expression.
Collapse
Affiliation(s)
| | - Başak Öztürk
- Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen, Braunschweig, Germany
| | - René De Mot
- Centre of Microbial and Plant Genetics, KU Leuven, Leuven, Belgium
| |
Collapse
|
11
|
Ghequire MGK, Öztürk B. A Colicin M-Type Bacteriocin from Pseudomonas aeruginosa Targeting the HxuC Heme Receptor Requires a Novel Immunity Partner. Appl Environ Microbiol 2018; 84:e00716-18. [PMID: 29980560 PMCID: PMC6121995 DOI: 10.1128/aem.00716-18] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Accepted: 06/28/2018] [Indexed: 12/16/2022] Open
Abstract
Pyocins are bacteriocins secreted by Pseudomonas aeruginosa, and they assist in the colonization of different niches. A major subset of these antibacterial proteins adopt a modular organization characteristic of polymorphic toxins. They include a receptor-binding domain, a segment enabling membrane passage, and a toxin module at the carboxy terminus, which eventually kills the target cells. To protect themselves from their own products, bacteriocin-producing strains express an immunity gene concomitantly with the bacteriocin. We show here that a pyocin equipped with a phylogenetically distinct ColM toxin domain, PaeM4, mediates antagonism against a large set of P. aeruginosa isolates. Immunity to PaeM4 is provided by the inner membrane protein PmiC, which is equipped with a transmembrane topology not previously described for the ColM family. Given that strains lacking a pmiC gene are killed by PaeM4, the presence of such an immunity partner likely is a key criterion for escaping cellular death mediated by PaeM4. The presence of a TonB box in PaeM4 and enhanced bacteriocin activity under iron-poor conditions strongly suggested the targeting of a TonB-dependent receptor. Evaluation of PaeM4 activities against TonB-dependent receptor knockout mutants in P. aeruginosa PAO1 revealed that the heme receptor HxuC (PA1302) serves as a PaeM4 target at the cellular surface. Because other ColM-type pyocins may target the ferrichrome receptor FiuA, our results illustrate the versatility in target recognition conferred by the polymorphic nature of ColM-type bacteriocins.IMPORTANCE The antimicrobial armamentarium of a bacterium is a major asset for colonizing competitive environments. Bacteriocins comprise a subset of these compounds. Pyocins are an example of such antibacterial proteins produced by Pseudomonas aeruginosa, killing other P. aeruginosa strains. A large group of these molecules show a modular protein architecture that includes a receptor-binding domain for initial target cell attachment and a killer domain. In this study, we have shown that a novel modular pyocin (PaeM4) that kills target bacteria via interference with peptidoglycan assembly takes advantage of the HxuC heme receptor. Cells can protect themselves from killing by the presence of a dedicated immunity partner, an integral inner membrane protein that adopts a transmembrane topology distinct from that of proteins currently known to provide immunity against such toxin activity. Understanding the receptors with which pyocins interact and how immunity to pyocins is achieved is a pivotal step toward the rational design of bacteriocin cocktails for the treatment of P. aeruginosa infections.
Collapse
Affiliation(s)
| | - Başak Öztürk
- Leibniz Institut DSMZ-German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany
| |
Collapse
|
12
|
Abstract
Bacteria host an arsenal of antagonism-mediating molecules to combat for ecologic space. Bacteriocins represent a pivotal group of secreted antibacterial peptides and proteins assisting in this fight, mainly eliminating relatives. Colicin M, a model for peptidoglycan-interfering bacteriocins in Gram-negative bacteria, appears to be part of a set of polymorphic toxins equipped with such a catalytic domain (ColM) targeting lipid II. Diversifying recombination has enabled parasitism of different receptors and has also given rise to hybrid bacteriocins in which ColM is associated with another toxin module. Remarkably, ColM toxins have recruited a diverse array of immunity partners, comprising cytoplasmic membrane-associated proteins with different topologies. Together, these findings suggest that different immunity mechanisms have evolved for ColM, in contrast to bacteriocins with nuclease activities.
Collapse
|
13
|
A Natural Chimeric Pseudomonas Bacteriocin with Novel Pore-Forming Activity Parasitizes the Ferrichrome Transporter. mBio 2017; 8:mBio.01961-16. [PMID: 28223456 PMCID: PMC5358913 DOI: 10.1128/mbio.01961-16] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Modular bacteriocins represent a major group of secreted protein toxins with a narrow spectrum of activity, involved in interference competition between Gram-negative bacteria. These antibacterial proteins include a domain for binding to the target cell and a toxin module at the carboxy terminus. Self-inhibition of producers is provided by coexpression of linked immunity genes that transiently inhibit the toxin's activity through formation of bacteriocin-immunity complexes or by insertion in the inner membrane, depending on the type of toxin module. We demonstrate strain-specific inhibitory activity for PmnH, a Pseudomonas bacteriocin with an unprecedented dual-toxin architecture, hosting both a colicin M domain, potentially interfering with peptidoglycan synthesis, and a novel colicin N-type domain, a pore-forming module distinct from the colicin Ia-type domain in Pseudomonas aeruginosa pyocin S5. A downstream-linked gene product confers PmnH immunity upon susceptible strains. This protein, ImnH, has a transmembrane topology similar to that of Pseudomonas colicin M-like and pore-forming immunity proteins, although homology with either of these is essentially absent. The enhanced killing activity of PmnH under iron-limited growth conditions reflects parasitism of the ferrichrome-type transporter for entry into target cells, a strategy shown here to be used as well by monodomain colicin M-like bacteriocins from pseudomonads. The integration of a second type of toxin module in a bacteriocin gene could offer a competitive advantage against bacteria displaying immunity against only one of both toxic activities.IMPORTANCE In their continuous struggle for ecological space, bacteria face a huge load of contenders, including phylogenetically related strains that compete for the same niche. One important group of secreted antibacterial proteins assisting in eliminating these rivals are modular bacteriocins of Gram-negative bacteria, comprising a domain for docking onto the cell envelope of a target cell, a translocation domain enabling subsequent cellular entry, and a toxin module that kills target cells via enzymatic or pore-forming activity. We here demonstrate the antagonistic function of a Pseudomonas bacteriocin with unique architecture that combines a putative enzymatic colicin M-like domain and a novel pore-forming toxin module. For target cell recognition and entry, this bacteriocin hybrid takes advantage of the ferrichrome transporter, also parasitized by enzymatic Pseudomonas bacteriocins devoid of the pore-forming module. Bacteriocins with an expanded toxin potential may represent an inventive bacterial strategy to alleviate immunity in target cells.
Collapse
|