Virophages of Giant Viruses: An Update at Eleven

Abstract

The last decade has been marked by two eminent discoveries that have changed our perception of the virology field: The discovery of giant viruses and a distinct new class of viral agents that parasitize their viral factories, the virophages. Coculture and metagenomics have actively contributed to the expansion of the virophage family by isolating dozens of new members. This increase in the body of data on virophage not only revealed the diversity of the virophage group, but also the relevant ecological impact of these small viruses and their potential role in the dynamics of the microbial network. In addition, the isolation of virophages has led us to discover previously unknown features displayed by their host viruses and cells. In this review, we present an update of all the knowledge on the isolation, biology, genomics, and morphological features of the virophages, a decade after the discovery of their first member, the Sputnik virophage. We discuss their parasitic lifestyle as bona fide viruses of the giant virus factories, genetic parasites of their genomes, and then their role as a key component or target for some host defense mechanisms during the tripartite virophage–giant virus–host cell interaction. We also present the latest advances regarding their origin, classification, and definition that have been widely discussed.

Giant virus vs amoeba: fight for supremacy

“…Their replication occurs in the giant virus factory and can be deleterious to viral replication, resulting in a decrease in amoebae lysis [15, 71] . Since their discovery, dozens of new virophages have been isolated and classified in a new viral family called Lavidaviridae [72–80]. It is believed that the virophage can mediate lateral gene transfer between giant viruses.…”

A virophage cross-species infection through mutant selection represses giant virus propagation, promoting host cell survival

“…Virophages are double-stranded (ds) DNA viruses that adopt a satellite-like lifestyle 6,7 . Studying the mechanism of host range in virophages is interesting because their replication requires the presence of two types of hosts, a giant virus and a cellular host of this giant virus, a protist.…”

Application of the omics sciences to the study of Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris: current status and future projections

“…These usually co-infect Acanthamoeba spp. cells, together with the Megaviruses, invading the transcription machinery used by the host-virus for its own subsistence, thus expanding the vision of viral variability in the environment [ 18 , 54 ].…”