Giant Viruses Have Genes for Their Own Metabolism

A team of researchers from Virginia Tech has discovered a significant collection of genes or building blocks in a diverse range of giant viruses. These genes are responsible for cellular metabolic cycles, which are a crucial characteristic of cellular life.

The research was published in Nature Communications where the researchers generated 501 metagenome-assembled genomes of Nucleo-Cytoplasmic Large DNA Viruses or NCLDV. They have gathered these from environments in various parts of the globe and analyzed their encoded functional capacity.

The researchers have observed a significant diversity of metabolic genes in prevalent giant viruses. Many of these metabolic genes involved nutrient uptake, nitrogen metabolism, and light-harvesting. As stated in their study, it came as a surprise to the researchers to have discovered that a lot of the NCLDV or giant viruses have preset components like glycolysis and TCA Cycle. These suggest that giant viruses can re-program certain essential aspects of their host's fundamental carbon metabolism.

Their findings reveal that large viruses program complex metabolic abilities with evolutionary histories that are mostly independent of cellular life. This finding strongly signifies that these giant viruses are crucial drivers of wide, global biogeochemical cycles.

Large DNA viruses challenge the common notion about viruses because the latter are the minutest resident of the microbiome, and they have a few genes of DNA or RNA that are gathered in a shell. They are so small that a small electron microscope is needed to see it. On the other hand, giant viruses are ten times the size of common compact viruses, and they contain hundreds or even thousands of genes within. These large viruses are so different than the rest of the virus family, that when scientists discovered the first species in 1992, they dismissed them as bacteria.

Frank Aylward, lead researcher and assistant professor of biological sciences in the Virginia Tech College of Science, explained that scientists often miss giant viruses in routine surveys because of a simple reason: their size is so big that filters meant to separate viruses from bacteria, and other big organisms catch them. So despite correctly classifying them earlier, scientists just considered them as isolated oddities.

Slowly, it became clear that these large DNA viruses are everywhere, and are particularly plentiful in aquatic environments. These giant viruses infect algae and protozoans, and the researchers emphasized that this discovery is crucial since the metabolism of the aforementioned single-celled organisms heavily affects and influences the conditions of the oceans, lakes, and other bodies of water where they live in, and eventually, affects the planet's carbon cycle.

Monir Moniruzzaman, the lead author of the study, used publicly available metagenome databases and by using known large DNA virus-genes as markers, and data from the patterns as clues, he pieced together genomes for the 501 giant viruses.

The team was surprised to see so many metabolic genes. Metabolism is a hallmark of cellular life, which is supposedly absent from viruses, and the metabolic genes discovered included many functions that had never been seen before in other viruses. The team has also explained that these genes are working mechanisms that the virus uses to commandeer its host, and this implies that it is responsible for alteration in the cell's metabolism.