Viruses are alive and deserve place on tree of life: Study

Viruses are siblings of humans and deserve a place on the tree of life, according to a new study.

While centuries of scientists had held that viruses were not living things, University of Illinois researchers found that viruses and cells shared hundreds of common protein structures which was solid evidence that the two shared closely-related ancestors.

"This tells you that you can build a tree of life, because you've found a multitude of features in viruses that have all the properties that cells have," said lead researcher Gustavo Caetano-Anollés, crop sciences and genomic biology professor at University of Illinois, Mailonline reported.

In the study, published in Science Advances journal, Caetano-Anollés and his graduate student, Arshan Nasir, state that early viruses were remarkably similar to the cells from which humans and modern organisms descended.

Historically, scientists had had difficulty determining where viruses came from due to their diversity and the fact that they evolved or mutated very fast.

Many scientists believe viruses were not part of the tree of life - suggesting that they could not be alive if they did not have metabolisms and they could not independently reproduce.

However, that argument overlooked the fact that viruses could form networks, the authors counter.

When viruses infected cells, taking over in order to reproduce, they acted much like many parasitic bacteria - which were fully accepted as living.

Until now, viruses had been difficult to classify, Caetano-Anollés said.

In its latest report, the International Committee on the Taxonomy of Viruses recognised seven orders of viruses, on the basis of their shapes and sizes, genetic structure and means of reproducing.

"Under this classification, viral families belonging to the same order have likely diverged from a common ancestral virus," wrote the authors. "However, only 26 (of 104) viral families have been assigned to an order, and the evolutionary relationships of most of them remain unclear."

Part of the confusion stemmed from the abundance and diversity of viruses. Less than 4,900 viruses had been identified and sequenced so far, even though according to scientists there were more than a million viral species.

Many viruses were tiny significantly smaller than bacteria or other microbes - and contain only a handful of genes, while others like the recently discovered mimiviruses, were huge, with genomes bigger than those of some bacteria.

Thanks to a system devised by biological engineers, it is now possible to tweak genomes of bacteria-eating viruses to target specific pathogens. (See: Scientists customise viruses to kill bacteria).