Scientists opened up the doors of the bizarre world of phages and brought never before seen monsters to the light. All over the planet, in various ecosystems, they found hundreds of unknown megaphages.
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The Scary Miniature World
Again and again, we get to be surprised by viruses. Their world is a wild world full of terror and violence on a cellular level where strange organisms live and despite all, we thought about life. Recently, scientists found many gigantic phages that we can easily call bacteria-eaters. These are monsters that are far bigger than common phages and can do things you would never expect from a virus.
Jill Banfield from the University of California, Berkeley and her coworkers are hunting for DNA sequences in various places of our planet. Really, for example, they pulled out DNA sequences from the intestines of unborn children and pregnant women, baboons, pigs, a hot spring in Tibet, a bioreactor in South Africa, hospital rooms, oceans, lakes, or even from the depths under the surface of the Earth.
Phages That Use CRISPR
Among DNA sequences that come from almost 30 such environments were 351 various gigantic phages. Phages are viruses that infect bacteria but the genomes of these megaphages were more than four times larger than the average genomes of phages scientists have seen until now. The largest one with a genome of 735 thousand bases is the largest phage we have ever seen and its genome is about fifteen times larger than the average phage. Seriously, if you met this phage in a dark alley you would be scared.
These megaphages not only attack but undoubtedly successfully destroy various bacteria. Many of them have sophisticated destructive weapons at their disposal that help them achieve their ominous goals. For example, some have a modified version of CRISPR which itself is originally a bacterial antiviral defense system. The megaphages adjusted it so when they attack a bacteria they pump parts of this CRISPR into it – mostly different variants of Cas proteins. Everything suggests they do this to point them towards fighting different phages. Thus, it is a weapon against their competition that is great at fighting remorseless viral battles that quietly rage everywhere around us – in every drop of water and on every grain of sand.
One of the discovered megaphages has the Cas phi protein in its weapon arsenal. Cas phi is an analog to the Cas9 protein which is part of the popular Cas9 genetic editor. This didn't go unnoticed by Banfield and her team and they say we could find many different, interesting, and useful tools for molecular laboratories. At this time, megaphages are full of genes about which we have no idea what their purpose is. So – a lot of fun for scientists.
But the megaphages also have genes we know well. Just that we have never seen them in viruses. Many different genes for transfer tRNA and its accompanying proteins or genes that have parts of the ribosome. That is unheard of. This is why the researchers say that megaphages sort of fill the void between the world of cells and viruses as viruses usually do not have ribosomes that belong to cells. And that just isn't enough – some of the megaphages have exotic, alternative genetic codes. And megaphages aren't monsters from some unique ecosystem – they are everywhere around us. We just do know practically nothing about them.
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