New Giant Virus Discovery Sparks Scientific Curiosity About the Origins of Life

Researchers reported that the virus was found in a freshwater pond near Tokyo, where it infects a species of amoeba, Vermamoeba vermiformis. They named it "Oshikovirus" after Oshiko-no-uma Pond in Ibaraki Prefecture. Amoebas are single-celled microscopic organisms typically found in water or damp environments and belong to the group Protozoa.

Giant viruses, the scientists explained, received little attention in the early decades of virology due to their large size, which caused them to be mistaken for bacteria. Recent studies, however, have revealed that these viruses are widespread in nature.

Despite their abundance, much of the evolutionary history of giant viruses remains unknown, and their classification as living organisms continues to generate scientific debate.

The researchers noted that the impact of viruses extends beyond disease. They can influence the evolution of organisms by transferring genes across species or integrating their genetic material into host cells, as retroviruses do. Studies indicate that remnants of ancient retroviruses make up roughly 8% of the human genome and have contributed to key vertebrate features, such as myelin production and placenta formation.

Scientists speculate that viruses may have played a central role in one of evolution’s major leaps: the transition from single-celled organisms to nucleated multicellular life. This hypothesis draws on the “viral eukaryogenesis” theory proposed by Masaharu Takemura in 2001, which suggests that the nucleus of eukaryotic cells originated from a large DNA virus that settled inside a primitive cell and gradually transformed into a nucleus.

Support for this theory has grown with the discovery of “viral factories” inside infected cells, structures that resemble and function like modern cell nuclei.

Since then, multiple types of giant viruses have been identified, including members of the Mimiviridae and Klosneuviridae families. However, isolating these viruses remains challenging, making the discovery of Oshikovirus a significant scientific achievement.

The new virus infects Vermamoeba vermiformis and shares some traits with other viruses, but it is unique in its ability to destroy the host’s nuclear membrane and create its own viral factory. It also forces infected cells to grow abnormally and has a distinctive protein shell, making it an important model for studying giant virus evolution.

Takemura, a co-author of the study, emphasized that giant viruses remain “an untapped scientific treasure,” and he expects that this discovery will deepen understanding of the relationship between viruses and living organisms. He added that finding a new Mimiviridae virus infecting a different host family will expand scientific knowledge and stimulate discussion about the classification and evolution of giant viruses.