Metabolic genes identified in giant viruses

The giant viruses, recently discovered, are organisms apart, even in their own class. Able to reach the size and genetic complexity of a bacterium, they also carry genes involved in metabolism according to a new scientific study.

There is a category apart in the world of virus, giant viruses. They can reach the size of a small bacterium, 1.5 µm, and their genome2.5 million base pairs for the largest. In comparison, the coronavirus SARS-CoV-2 is only a hundred nanometers and its genome contains only 29,000 base pairs.

Their size and complexity therefore place them on the border of the living, those who are considered non-living. Definitions of this term vary, but it is commonly accepted that a living organism must be able to produce its own energy through a set of cellular reactions called metabolism.

Viruses carry in their genome the genetic elements essential for the replication of their genome and the construction of their protein structures. But for metabolic reactions, they depend entirely on the cell they parasitize. For example, this will provide the ribosomes for the translation of protein, and all the energy needed to assemble the virus despite its survival.

Despite this, researchers from Virginia Tech in the United States built 501 giant virus genomes from literature data and found traces of Genoa metabolic. Their results are published in Nature Communication.

Viral metabolic genes

The study of 501 genomes, mostly belonging to giant viruses infecting single-celled aquatic organisms, first revealed the obvious: giant viruses have genes to replicate their material genetic and produce their structural proteins. But scientists did not expect to find as many genes linked to metabolic functions specific to living cells.

Bioinformatics analysis revealed the presence of genes close to those regulating oxidative stress, cell stress potentially lethal which must be checked. Others are involved in the photosynthesis and transportation of nutrient. Their presence would allow viruses to divert these functions to their advantage during infection.

If these metabolic genes are not the first identified in giant viruses, it is the first time that such a diversity has been discovered. Obviously, alone, these genes cannot form a functional metabolism but testify to past infections.

The legacy of old infections

Researchers believe they were acquired by chance over the course of infections. Some viral genes are very close to their cellular version, but they still carry genetic markers specific to viruses.

Microalgae play a predominant role in the cycle of carbon in lakes and oceans. Understanding giant viruses also allows us to understand their impact on biogeochemical cycles. The researchers who worked on this study now want to understand how these genes interact with cell metabolism and when they were acquired. Although not alive, viruses have a major role in ecosystems living.

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