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Mozumdar D, Fossati A, Stevenson E, Guan J, Nieweglowska E, Rao S, Agard D, Swaney DL, Bondy-Denomy J. Characterization of a lipid-based jumbo phage compartment as a hub for early phage infection. Cell Host Microbe 2024; 32:1050-1058.e7. [PMID: 38870941 PMCID: PMC11239273 DOI: 10.1016/j.chom.2024.05.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2024] [Revised: 05/03/2024] [Accepted: 05/17/2024] [Indexed: 06/15/2024]
Abstract
Viral genomes are most vulnerable to cellular defenses at the start of the infection. A family of jumbo phages related to phage ΦKZ, which infects Pseudomonas aeruginosa, assembles a protein-based phage nucleus to protect replicating phage DNA, but how it is protected prior to phage nucleus assembly is unclear. We find that host proteins related to membrane and lipid biology interact with injected phage protein, clustering in an early phage infection (EPI) vesicle. The injected virion RNA polymerase (vRNAP) executes early gene expression until phage genome separation from the vRNAP and the EPI vesicle, moving into the nascent proteinaceous phage nucleus. Enzymes involved in DNA replication and CRISPR/restriction immune nucleases are excluded by the EPI vesicle. We propose that the EPI vesicle is rapidly constructed with injected phage proteins, phage DNA, host lipids, and host membrane proteins to enable genome protection, early transcription, localized translation, and to ensure faithful genome transfer to the proteinaceous nucleus.
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Affiliation(s)
- Deepto Mozumdar
- Department of Immunology and Microbiology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Andrea Fossati
- J. David Gladstone Institutes, San Francisco, CA 94158, USA; Quantitative Biosciences Institute (QBI), University of California, San Francisco, San Francisco, CA 94158, USA; Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Erica Stevenson
- J. David Gladstone Institutes, San Francisco, CA 94158, USA; Quantitative Biosciences Institute (QBI), University of California, San Francisco, San Francisco, CA 94158, USA; Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Jingwen Guan
- Department of Immunology and Microbiology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Eliza Nieweglowska
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Sanjana Rao
- Department of Immunology and Microbiology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - David Agard
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA; Chan Zuckerberg Imaging Institute, Redwood City, CA 94065, USA
| | - Danielle L Swaney
- J. David Gladstone Institutes, San Francisco, CA 94158, USA; Quantitative Biosciences Institute (QBI), University of California, San Francisco, San Francisco, CA 94158, USA; Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Joseph Bondy-Denomy
- Department of Immunology and Microbiology, University of California, San Francisco, San Francisco, CA 94158, USA; Quantitative Biosciences Institute (QBI), University of California, San Francisco, San Francisco, CA 94158, USA.
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2
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Prichard A, Pogliano J. The intricate organizational strategy of nucleus-forming phages. Curr Opin Microbiol 2024; 79:102457. [PMID: 38581914 DOI: 10.1016/j.mib.2024.102457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2024] [Revised: 03/01/2024] [Accepted: 03/08/2024] [Indexed: 04/08/2024]
Abstract
Nucleus-forming phages (chimalliviruses) encode numerous genes responsible for creating intricate structures for viral replication. Research on this newly appreciated family of phages has begun to reveal the mechanisms underlying the subcellular organization of the nucleus-based phage replication cycle. These discoveries include the structure of the phage nuclear shell, the identification of a membrane-bound early phage infection intermediate, the dynamic localization of phage RNA polymerases, the phylogeny and core genome of chimalliviruses, and the variation in replication mechanisms across diverse nucleus-forming phages. This research is being propelled forward through the application of fluorescence microscopy and cryo-electron microscopy and the innovative use of new tools such as proximity labeling and RNA-targeting Clustered Regularly Interspaced Short Palindromic Repeats-Cas systems.
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Affiliation(s)
- Amy Prichard
- School of Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Joe Pogliano
- School of Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA.
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3
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Enustun E, Deep A, Gu Y, Nguyen KT, Chaikeeratisak V, Armbruster E, Ghassemian M, Villa E, Pogliano J, Corbett KD. Identification of the bacteriophage nucleus protein interaction network. Nat Struct Mol Biol 2023; 30:1653-1662. [PMID: 37667030 PMCID: PMC10643120 DOI: 10.1038/s41594-023-01094-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 08/11/2023] [Indexed: 09/06/2023]
Abstract
In the arms race between bacteria and bacteriophages (phages), some large-genome jumbo phages have evolved a protein shell that encloses their replicating genome to protect it against host immune factors. By segregating the genome from the host cytoplasm, however, the 'phage nucleus' introduces the need to specifically translocate messenger RNA and proteins through the nuclear shell and to dock capsids on the shell for genome packaging. Here, we use proximity labeling and localization mapping to systematically identify proteins associated with the major nuclear shell protein chimallin (ChmA) and other distinctive structures assembled by these phages. We identify six uncharacterized nuclear-shell-associated proteins, one of which directly interacts with self-assembled ChmA. The structure and protein-protein interaction network of this protein, which we term ChmB, suggest that it forms pores in the ChmA lattice that serve as docking sites for capsid genome packaging and may also participate in messenger RNA and/or protein translocation.
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Affiliation(s)
- Eray Enustun
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
| | - Amar Deep
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA
| | - Yajie Gu
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA
| | - Katrina T Nguyen
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
| | - Vorrapon Chaikeeratisak
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
- Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
| | - Emily Armbruster
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
| | - Majid Ghassemian
- Biomolecular and Proteomics Mass Spectrometry Facility, University of California San Diego, La Jolla, CA, USA
| | - Elizabeth Villa
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
- Howard Hughes Medical Institute, La Jolla, CA, USA
| | - Joe Pogliano
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA.
| | - Kevin D Corbett
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA.
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA.
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4
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Enustun E, Deep A, Gu Y, Nguyen KT, Chaikeeratisak V, Armbruster E, Ghassemian M, Villa E, Pogliano J, Corbett KD. Identification of the bacteriophage nucleus protein interaction network. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.18.541317. [PMID: 37292858 PMCID: PMC10245766 DOI: 10.1101/2023.05.18.541317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
In the arms race between bacteria and bacteriophages (phages), some large-genome jumbo phages have evolved a protein shell that encloses their replicating genome to protect it against DNA-targeting immune factors. By segregating the genome from the host cytoplasm, however, the "phage nucleus" introduces the need to specifically transport mRNA and proteins through the nuclear shell, and to dock capsids on the shell for genome packaging. Here, we use proximity labeling and localization mapping to systematically identify proteins associated with the major nuclear shell protein chimallin (ChmA) and other distinctive structures assembled by these phages. We identify six uncharacterized nuclear shell-associated proteins, one of which directly interacts with self-assembled ChmA. The structure and protein-protein interaction network of this protein, which we term ChmB, suggests that it forms pores in the ChmA lattice that serve as docking sites for capsid genome packaging, and may also participate in mRNA and/or protein transport.
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Affiliation(s)
- Eray Enustun
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
| | - Amar Deep
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA
| | - Yajie Gu
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA
| | - Katrina T. Nguyen
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
| | - Vorrapon Chaikeeratisak
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
- Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
| | - Emily Armbruster
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
| | - Majid Ghassemian
- Biomolecular and Proteomics Mass Spectrometry Facility, University of California San Diego, La Jolla, CA, USA
| | - Elizabeth Villa
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
- Howard Hughes Medical Institute, La Jolla, California, USA
| | - Joe Pogliano
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
| | - Kevin D. Corbett
- Department of Molecular Biology, University of California San Diego, La Jolla, CA, USA
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA
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5
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Gao D, Ji H, Li X, Ke X, Li X, Chen P, Qian P. Host receptor identification of a polyvalent lytic phage GSP044, and preliminary assessment of its efficacy in the clearance of Salmonella. Microbiol Res 2023; 273:127412. [PMID: 37243984 DOI: 10.1016/j.micres.2023.127412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2023] [Revised: 05/15/2023] [Accepted: 05/16/2023] [Indexed: 05/29/2023]
Abstract
Salmonella and pathogenic Escherichia coli are important foodborne pathogens. Phages are being recognized as potential antibacterial agents to control foodborne pathogens. In the current study, a polyvalent broad-spectrum phage, GSP044, was isolated from pig farm sewage. It can simultaneously lyse many different serotypes of Salmonella and E. coli, exhibiting a broad host range. Using S. Enteritidis SE006 as the host bacterium, phage GSP044 was further characterized. GSP044 has a short latent period (10 min), high stability at different temperatures and pH, and good tolerance to chloroform. Genome sequencing analysis revealed that GSP044 has a double-stranded DNA (dsDNA) genome consisting of 110,563 bp with G + C content of 39%, and phylogenetic analysis of the terminase large subunit confirmed that GSP044 belonged to the Demerecviridae family, Epseptimavirus genus. In addition, the genomic sequence did not contain any lysogenicity-related, virulence-related, or antibiotic resistance-related genes. Analysis of phage-targeted host receptors revealed that the outer membrane protein (OMP) BtuB was identified as a required receptor for phage infection of host bacteria. The initial application capability of phage GSP044 was assessed using S. Enteritidis SE006. Phage GSP044 could effectively reduce biofilm formation and degrade the mature biofilm in vitro. Moreover, GSP044 significantly decreased the viable counts of artificially contaminated S. Enteritidis in chicken feed and drinking water. In vivo tests, a mouse model of intestinal infection demonstrated that phage GSP044 was able to reduce the number of colonized S. Enteritidis in the intestine. These results suggest that phage GSP044 may be a promising candidate biologic agent for controlling Salmonella infections.
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Affiliation(s)
- Dongyang Gao
- National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, the Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, People's Republic of China
| | - Hongyue Ji
- National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, the Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, People's Republic of China
| | - Xin Li
- National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, the Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, People's Republic of China
| | - Xiquan Ke
- National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, the Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, People's Republic of China
| | - Xiangmin Li
- National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, the Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, People's Republic of China
| | - Pin Chen
- National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, the Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, People's Republic of China.
| | - Ping Qian
- National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei 430070, People's Republic of China; Key Laboratory of Preventive Veterinary Medicine in Hubei Province, the Cooperative Innovation Center for Sustainable Pig Production, Wuhan, Hubei 430070, People's Republic of China.
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6
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Mass Spectral Analyses of Salmonella Myovirus SPN3US Reveal Conserved and Divergent Themes in Proteolytic Maturation of Large Icosahedral Capsids. Viruses 2023; 15:v15030723. [PMID: 36992431 PMCID: PMC10052503 DOI: 10.3390/v15030723] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 03/07/2023] [Accepted: 03/08/2023] [Indexed: 03/16/2023] Open
Abstract
Salmonella myovirus SPN3US has a T = 27 capsid composed of >50 different gene products, including many that are packaged along with the 240 kb genome and ejected into the host cell. Recently, we showed that an essential phage-encoded prohead protease gp245 is responsible for cleavage of proteins during SPN3US head assembly. This proteolytic maturation step induces major changes in precursor head particles, enabling them to expand and undergo genome packaging. To comprehensively define the composition of the mature SPN3US head and elucidate how it is modified by proteolysis during assembly, we conducted tandem mass spectrometry analysis of purified virions and tailless heads. Fourteen protease cleavage sites were identified in nine proteins, including eight sites not previously identified in head proteins in vivo. Among these was the maturation cleavage site of gp245 which was identical to the autocleavage site we had previously identified in purified recombinant gp245. Our findings underscore the value of employing multiple mass spectrometry-based experimental strategies as a way to enhance the detection of head protein cleavage sites in tailed phages. In addition, our results have identified a conserved set of head proteins in related giant phages that are similarly cleaved by their respective prohead proteases, suggesting that these proteins have important roles in governing the formation and function of large icosahedral capsids.
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7
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The Beauty of Bacteriophage T4 Research: Lindsay W. Black and the T4 Head Assembly. Viruses 2022; 14:v14040700. [PMID: 35458430 PMCID: PMC9026906 DOI: 10.3390/v14040700] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 03/22/2022] [Accepted: 03/23/2022] [Indexed: 02/06/2023] Open
Abstract
Viruses are biochemically complex structures and mainly consist of folded proteins that contain nucleic acids. Bacteriophage T4 is one of most prominent examples, having a tail structure that contracts during the infection process. Intracellular phage multiplication leads to separate self-directed assembly reactions of proheads, tails and tail fibers. The proheads are packaged with concatemeric DNA produced by tandem replication reactions of the parental DNA molecule. Once DNA packaging is completed, the head is joined with the tail and six long fibers are attached. The mature particles are then released from the cell via lysis, another tightly regulated process. These processes have been studied in molecular detail leading to a fascinating view of the protein-folding dynamics that direct the structural interplay of assembled complexes. Lindsay W. Black dedicated his career to identifying and defining the molecular events required to form the T4 virion. He leaves us with rich insights into the astonishingly precise molecular clockwork that co-ordinates all of the players in T4 assembly, both viral and cellular. Here, we summarize Lindsay’s key research contributions that are certain to stimulate our future science for many years to come.
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Laughlin TG, Deep A, Prichard AM, Seitz C, Gu Y, Enustun E, Suslov S, Khanna K, Birkholz EA, Armbruster E, McCammon JA, Amaro RE, Pogliano J, Corbett KD, Villa E. Architecture and self-assembly of the jumbo bacteriophage nuclear shell. Nature 2022; 608:429-435. [PMID: 35922510 PMCID: PMC9365700 DOI: 10.1038/s41586-022-05013-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 06/22/2022] [Indexed: 12/26/2022]
Abstract
Bacteria encode myriad defences that target the genomes of infecting bacteriophage, including restriction-modification and CRISPR-Cas systems1. In response, one family of large bacteriophages uses a nucleus-like compartment to protect its replicating genomes by excluding host defence factors2-4. However, the principal composition and structure of this compartment remain unknown. Here we find that the bacteriophage nuclear shell assembles primarily from one protein, which we name chimallin (ChmA). Combining cryo-electron tomography of nuclear shells in bacteriophage-infected cells and cryo-electron microscopy of a minimal chimallin compartment in vitro, we show that chimallin self-assembles as a flexible sheet into closed micrometre-scale compartments. The architecture and assembly dynamics of the chimallin shell suggest mechanisms for its nucleation and growth, and its role as a scaffold for phage-encoded factors mediating macromolecular transport, cytoskeletal interactions, and viral maturation.
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Affiliation(s)
- Thomas G. Laughlin
- grid.266100.30000 0001 2107 4242Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA USA
| | - Amar Deep
- grid.266100.30000 0001 2107 4242Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA USA
| | - Amy M. Prichard
- grid.266100.30000 0001 2107 4242Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA USA
| | - Christian Seitz
- grid.266100.30000 0001 2107 4242Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA USA
| | - Yajie Gu
- grid.266100.30000 0001 2107 4242Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA USA
| | - Eray Enustun
- grid.266100.30000 0001 2107 4242Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA USA
| | - Sergey Suslov
- grid.266100.30000 0001 2107 4242Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA USA
| | - Kanika Khanna
- grid.266100.30000 0001 2107 4242Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA USA ,grid.47840.3f0000 0001 2181 7878Present Address: Department of Molecular and Cell Biology, University of California, Berkeley, CA USA
| | - Erica A. Birkholz
- grid.266100.30000 0001 2107 4242Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA USA
| | - Emily Armbruster
- grid.266100.30000 0001 2107 4242Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA USA
| | - J. Andrew McCammon
- grid.266100.30000 0001 2107 4242Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA USA ,grid.266100.30000 0001 2107 4242Department of Pharmacology, University of California San Diego, La Jolla, CA USA
| | - Rommie E. Amaro
- grid.266100.30000 0001 2107 4242Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA USA
| | - Joe Pogliano
- Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA, USA.
| | - Kevin D. Corbett
- grid.266100.30000 0001 2107 4242Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA USA ,grid.266100.30000 0001 2107 4242Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA USA
| | - Elizabeth Villa
- Department of Molecular Biology, School of Biological Sciences, University of California San Diego, La Jolla, CA, USA. .,Howard Hughes Medical Institute, University of California San Diego, La Jolla, CA, USA.
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Maturation of Pseudo-Nucleus Compartment in P. aeruginosa, Infected with Giant phiKZ Phage. Viruses 2020; 12:v12101197. [PMID: 33096802 PMCID: PMC7589130 DOI: 10.3390/v12101197] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 10/19/2020] [Accepted: 10/19/2020] [Indexed: 12/25/2022] Open
Abstract
The giant phiKZ phage infection induces the appearance of a pseudo-nucleus inside the bacterial cytoplasm. Here, we used RT-PCR, fluorescent in situ hybridization (FISH), electron tomography, and analytical electron microscopy to study the morphology of this unique nucleus-like shell and to demonstrate the distribution of phiKZ and bacterial DNA in infected Pseudomonas aeruginosa cells. The maturation of the pseudo-nucleus was traced in short intervals for 40 min after infection and revealed the continuous spatial separation of the phage and host DNA. Immediately after ejection, phage DNA was located inside the newly-identified round compartments; at a later infection stage, it was replicated inside the pseudo-nucleus; in the mature pseudo-nucleus, a saturated internal network of filaments was observed. This network consisted of DNA bundles in complex with DNA-binding proteins. On the other hand, the bacterial nucleoid underwent significant rearrangements during phage infection, yet the host DNA did not completely degrade until at least 40 min after phage application. Energy dispersive x-ray spectroscopy (EDX) analysis revealed that, during the infection, the sulfur content in the bacterial cytoplasm increased, which suggests an increase of methionine-rich DNA-binding protein synthesis, whose role is to protect the bacterial DNA from stress caused by infection.
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