The border between the living and non-living world is now more blurred: the missing link that unites these two worlds has been discovered and is a virus never seen, much larger than its peers and above all equipped with a set of proteins characteristic of bacteria. The discovery, published in the journal Nature, for the first time dissolves the boundary that has so far separated machine-like parasites, such as viruses, from living organisms; it could also provide new weapons for the medicine of the future.
Graphical representation of a bacteriophage (source: Pixabay)
The discovery is due to the group of the University of California in Berkeley led by Jill Banfield with Basem Al-Shayeb, in collaboration with Canada, Denmark and Japan. Although new viruses are present everywhere on Earth, finding them was only possible thanks to the largest research on microorganisms on the planet, which has reviewed 30 environments: from Tibetan sources to hospitals, from the oceans and the subsoil to pregnant women.
"These large viruses form the bridge between non-living bacteriophages and bacteria," observed Banfield, "hybrids between traditional viruses and traditional living organisms." They belong to the family of virus parasites of bacteria, called bacteriophages (or phages), and are anomalous not only for their size, really very large, but because they contain genes that are usually found in bacteria. At least 351 were found, divided into 10 groups, each of which is called 'large' in the languages of the authors of the research, from Arabic to Chinese.
The genealogical tree of bacteriophages. On the left the names of the ten identified groups (source: UC Berkeley, Jill Banfield lab)
All new phages are at least four times larger than their cousins in the inanimate world; the largest has a genetic make-up of 735,000 base pairs: even greater than that of a bacterium. Digging inside these gene packs, a truly surprising set of tools emerged, between enzymes and proteins, including those used in the DNA cut-paste technique, called Crispr .
Graphical representation of a bacteriophage that infects a bacterium (source: UC Berkeley, Jill Banfield lab)
One is the impersonator of the Cas-9 molecular scissors discovered in bacteria and recognized by Jennifer Doudna, who with Emmanuelle Charpentier has developed the technique and who is among the authors of the research. He called it Cas-Phi, where Phi is the Greek letter for phages. Furthermore, in the same issue of Nature, Doudna signs another article, which reviews the future applications of Crispr.
"Having found a protein similar to Cas-9 is the proof that was missing to understand where the ability of bacteria to defend against viruses came from," commented the director of the Laboratory of Development Biology of the University of Pavia, Carlo Alberto Redi . "Having found it in viruses - he added - opens new doors to many applications and constitutes a remarkable therapeutic opening to face them".
A potential of which the authors of the research are perfectly aware: "in these large bacteriophages there is enormous potential for discovering new tools for genetic engineering," said Rohan Sachdeva. "Many of these genes are unknown, have no identified function and could be a source of new proteins for industrial, medical or agricultural applications."