Carpe pili! Hunting strategy, structure, and replication of P. aeruginosa phage JBD30
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| Year of publication | 2024 |
| Type | Appeared in Conference without Proceedings |
| MU Faculty or unit | |
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| Description | Phages are the most abundant biological entities on Earth, but our understanding of many aspects of their lifecycles is still incomplete. Here, we have used cryo-electron and fluorescence microscopy to analyze the replication cycle of the siphophage Casadabanvirus JBD30. Phage JBD30 is atemperate phage that infects the bacterium Pseudomonas aeruginosa, a human pathogen known for causing infections that are often difficult to treat due to its multidrug resistance2,3.The virion of phage JBD30 consists of an icosahedral capsid, connector, long flexible non-contractile tail, and abaseplate equipped with the tail fibres. These tail fibres attach to P. aeruginosa type IV pilus. Type IV pili are thin filaments growing from the cell poles that the bacteria repeatedly extend and retract to move over surfaces4. The retraction of the pilus brings the phage to the bacterial cell surface. The interaction between the baseplate and the pilus orients the JBD30 virion so that the tripod of receptor-binding proteins faces the bacterial surface, ensuring proper orientation of the baseplate for cell attachment and genome ejection. Subsequently, the tripod of receptor-binding proteins attaches to the outer bacterial membrane and slides aside, triggering the opening of the baseplate, leading to the release of three copies of the tape-measure protein. The release of the tail tape measure proteins triggers DNA ejection. For replication, phage DNA redistributes from the cell poles throughout the cytoplasm.Capsids of JBD30 progeny are assembled as procapsids, which expand by 7% in diameter upon filling with newly synthesized dsDNA. The DNA-filled heads are then joined with 180-nm-long tails. The tails assemble independently by polymerization of major tail proteins around the tape measure protein into hexameric discs. The bending of the tail tube is allowed by the flexible loops of the major tail protein that mediate the contacts between successive tail discs. The JBD30 replication cycle ends with host cell lysis and the release of phage progeny. The first virions occur at 80 min post-infection, and the titer peaks at 100 min post-infection.The combination of cryo-electron tomography and fluorescent microscopy has enabled the characterization of the replication cycle of phage JBD30, shedding light on its intricate mechanisms of host cell recognition, genome delivery, and progeny particle formation. It is likely that the structural features and replication mechanisms described here for phage JBD30 are conserved among siphophages that utilize bacterial type IV pili for initial cell attachment. |
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