Scientists are listening in on the ways viruses communicate and cooperate. Decoding what the microbes are saying could be a boon to human health.
Geneticist Rotem Sorek could see that his bacteria were sick — so far, so good. He had deliberately infected them with a virus to test whether each ailing microbe soldiered on alone or communicated with its allies to fight the attack.
But when he and his team at the Weizmann Institute of Science in Rehovot, Israel, looked into the contents of their flasks, they saw something completely unexpected: the bacteria were silent, and it was the viruses that were chattering away, passing notes to each other in a molecular language only they could understand. They were deciding together when to lie low in the host cell and when to replicate and burst out, in search of new victims.
It was an accidental discovery that would fundamentally change scientists’ understanding of how viruses behave.
Viruses that infect bacteria — spiky lollipop-like creatures known as bacteriophages (or phages) — have surveillance mechanisms that bring them intel on whether to stay dormant or attack, depending on the availability of fresh victims. But researchers long thought these processes were passive; the phages seemed to just sit back and listen in, waiting for bacterial distress signals to reach fever pitch before taking action.
Sorek and his colleagues had found phages actively discussing their choices. They realized that as a phage infects a cell, it releases a tiny protein — a peptide just six amino acids long — that serves as a message to its brethren: “I’ve taken a victim”. As the phages infect more cells, the message gets louder, signalling that uninfected hosts are becoming scarce. Phages then put a halt to lysis — the process of replicating and breaking out of their hosts — instead staying hidden in a sluggish state called lysogeny.
The viruses, it turns out, did not depend on bacterial cues to make their decisions. They controlled their own destiny. “This finding was a big, important, revolutionary concept in virology,” says Wei Cheng, a structural microbiologist at Sichuan University in Chengdu, China.
Sorek named this viral peptide ‘arbitrium’, after the Latin word for decision. It seemed to work much like the communication system used by bacteria — quorum sensing — to share information about cell density and adjust the population accordingly. Yet it was the first time anyone had demonstrated molecular messaging of this kind in viruses. And it fitted into an emerging picture of viruses as much more sophisticated social agents than scientists had given them credit for.
Virologists have long studied their subjects in isolation, targeting cells with just a single viral particle. But it’s become increasingly clear that many viruses cooperate, teaming up to co-infect hosts and break down antiviral immune defences.
The implication is that researchers might have been going about their experiments all wrong. “It has shaken one of the pillars of virology,” says Sam Díaz-Muñoz, an evolutionary biologist at the University of California, Davis.
Learning the language behind these viral interactions could inform the design of new treatments for cancer and nasty superinfections. The social predilections of viruses even help to explain how they evade the bacterial immune system known as CRISPR. “Conceptually, it’s really powerful,” Díaz-Muñoz says.
To read more, Source: https://www.nature.com/articles/d41586-019-01880-6
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