Biological Trajectory of Virophage Research and the Emergence of Marine Virophages: A Scoping Review

Virophages are satellite viruses that depend on the replication machinery of giant double-stranded DNA viruses and influence the structure and dynamics of viral communities through multilayered interactions among giant viruses, their hosts, and virophages. Since the discovery of the Sputnik virophage in 2008, virophages have been increasingly recognized for their roles in regulating giant virus replication, contributing to host defense mechanisms, and shaping the evolution of mobile genetic elements. However, quantitative syntheses examining how virophage research has developed over time, particularly in marine environments, remain limited. Here, we conducted a bibliometric analysis of virophage research published between 2008 and 2025 using the Web of Science Core Collection. By comparing an overall virophage research corpus with a marine virophage sub-corpus, we assessed publication and citation trends, collaboration structures, and keyword-based intellectual and thematic evolution. Our results show that virophage research has gradually transitioned from an early phase dominated by landmark discoveries and experimental model systems to a data-intensive stage driven by genome- and metagenome-based analyses and computational approaches. Although marine virophage studies represent a relatively small proportion of the total literature, they exhibit sustained citation impact and form a distinct research axis within the field. In particular, marine-focused studies emphasize metagenomic discovery, genome sequence alignment, and the analysis of mobile genetic elements such as polinton-like viruses, highlighting the role of marine environments in accelerating the intellectual transition of virophage research. Collectively, these findings demonstrate that virophage research has moved beyond a "discovery and definition" phase toward data-driven integrative interpretation, with marine virophage research emerging as a key domain for understanding the structure and evolutionary dynamics of marine viral ecosystems.