Structure of NO16, a marine non-tailed vibriophage with an unusual symmetry-mismatched vertex arrangement
5 affiliations
- 1Department of Macromolecular Structures, Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain
- 2Escuela de Doctorado, Universidad Autónoma de Madrid, Madrid, Spain
- 3Globe Institute, Center for Evolutionary Hologenomics, University of Copenhagen, Copenhagen, Denmark
- 4Department of Biology, Marine Biological Section, University of Copenhagen, Copenhagen, Denmark
- 5HADAL & Nordcee, Department of Biology, University of Southern Denmark, Odense, Denmark
Abstract
Non-tailed phages remain underexplored in marine environments, as tailed phages have long dominated sequence and culture collections. Yet recent surveys suggest that non-tailed phages may be more abundant and have distinct impacts on microbial mortality and gene transfer. Here, we solve the structure of Vibrio anguillarum bacteriophage NO16, one of the simplest members of the Varidnaviria realm. Mass spectrometry detected at least nine different proteins in the virion, which has a pseudoT = 21 capsid similar to that of related double jelly roll (DJR) phages, but differs in the organization of minor capsid proteins, particularly those mediating membrane-capsid contacts. The DJR major capsid protein GP19 is stabilized by strong electrostatic interactions between monomers, and possibly by a cation at its base, as seen in corticovirus PM2. Localized reconstruction revealed a symmetry mismatch at the vertex, where two trimeric GP13 spikes attach to the pentameric GP14 penton base. GP13 carbohydrate-binding sites and predicted glycosylase activity point to a role in host entry. Using structural and functional predictions for its entire proteome, we propose a complete atlas of the NO16 infectious cycle. Author summary: Bacteriophages are among the most abundant biological entities in the oceans. While most known phages use a tail to recognize and infect bacteria, simpler non-tailed phages may be just as important in marine ecosystems. NO16 is one such virus and infects Vibrio anguillarum, a bacterium that causes disease in fish farms. Here, we determined the three-dimensional structure of NO16 and identified the proteins that build the virus particle. We found that NO16 is one of the simplest known members of an ancient viral lineage found across all domains of life. Despite its simplicity, it contains an unusual arrangement of vertex proteins that likely recognize sugars on the bacterial surface and help the virus enter its host. By combining structural biology with protein function predictions, we also reconstructed the likely steps of the NO16 infectious cycle. Our findings provide new insight into this overlooked group of marine viruses and their evolution.
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BibTeX
@article{otaegiugartemendia2026structure,
title = {{Structure of NO16, a marine non-tailed vibriophage with an unusual symmetry-mismatched vertex arrangement}},
author = {Sara Otaegi-Ugartemendia and Gabriela N. Condezo and Marta Martínez and Panos G. Kalatzis and Mathias Middelboe and Carmen San Martín},
journal = {PLOS Pathogens},
year = {2026},
month = sep,
doi = {10.1371/journal.ppat.1014525},
url = {https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014525},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Structure of NO16, a marine non-tailed vibriophage with an unusual symmetry-mismatched vertex arrangement
AU - Sara Otaegi-Ugartemendia
AU - Gabriela N. Condezo
AU - Marta Martínez
AU - Panos G. Kalatzis
AU - Mathias Middelboe
AU - Carmen San Martín
PY - 2026
DA - 2026/09/08
JO - PLOS Pathogens
DO - 10.1371/journal.ppat.1014525
UR - https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014525
AB - Non-tailed phages remain underexplored in marine environments, as tailed phages have long dominated sequence and culture collections. Yet recent surveys suggest that non-tailed phages may be more abundant and have distinct impacts on microbial mortality and gene transfer. Here, we solve the structure of Vibrio anguillarum bacteriophage NO16, one of the simplest members of the Varidnaviria realm. Mass spectrometry detected at least nine different proteins in the virion, which has a pseudoT = 21 capsid similar to that of related double jelly roll (DJR) phages, but differs in the organization of minor capsid proteins, particularly those mediating membrane-capsid contacts. The DJR major capsid protein GP19 is stabilized by strong electrostatic interactions between monomers, and possibly by a cation at its base, as seen in corticovirus PM2. Localized reconstruction revealed a symmetry mismatch at the vertex, where two trimeric GP13 spikes attach to the pentameric GP14 penton base. GP13 carbohydrate-binding sites and predicted glycosylase activity point to a role in host entry. Using structural and functional predictions for its entire proteome, we propose a complete atlas of the NO16 infectious cycle. Author summary: Bacteriophages are among the most abundant biological entities in the oceans. While most known phages use a tail to recognize and infect bacteria, simpler non-tailed phages may be just as important in marine ecosystems. NO16 is one such virus and infects Vibrio anguillarum, a bacterium that causes disease in fish farms. Here, we determined the three-dimensional structure of NO16 and identified the proteins that build the virus particle. We found that NO16 is one of the simplest known members of an ancient viral lineage found across all domains of life. Despite its simplicity, it contains an unusual arrangement of vertex proteins that likely recognize sugars on the bacterial surface and help the virus enter its host. By combining structural biology with protein function predictions, we also reconstructed the likely steps of the NO16 infectious cycle. Our findings provide new insight into this overlooked group of marine viruses and their evolution.
SN - 1553-7374
ER -