Siphoviruses
Siphoviridae
Siphoviridae is a family of viruses in the order Caudovirales that infect bacteria and archaea. They possess an icosahedral capsid and a characteristic long, flexible, non-contractile tail. Their genetic material consists of linear double-stranded DNA. In aquatic ecosystems, they are significantly involved in the 'viral shunt' by converting biomass back into dissolved organic matter through cell lysis.
Details
Identification
Icosahedral capsid (approx. 60 nm diameter), long flexible tail (up to 500 nm), non-enveloped, dsDNA genome.
Diet
Obligate parasites; they infect specific bacterial hosts and utilize their metabolism for replication.
Hunting strategy
Adsorption to specific receptors on the host cell wall via specialized tail structures.
Overwintering
Persistence as a prophage within the host genome (lysogeny) or as viral particles in the environment.
Ecology
Ecological role
Regulation of bacterial density, promotion of nutrient cycling, and enabling horizontal gene transfer.
Natural predators
Degradation by extracellular enzymes, UV radiation, and ingestion by heterotrophic nanoflagellates.
Competitor species
Other bacteriophage families (e.g., Myoviridae, Podoviridae) that infect the same host strains.
Ecosystem service
Control of bacterial blooms and maintenance of microbial diversity in water bodies.
Scientific profile
Profile
Habitat
Ubiquitous in all ecosystems where bacteria are present: oceans, freshwater, soil, deep-sea sediments, and as part of the microbiome in animals and humans.
Ecological role
Essential role in the 'viral shunt'; by lysing bacteria, nutrients (C, N, P) are cycled back into the dissolved organic matter (DOM) pool, supporting the microbial food web.