This Megavirus has its own CRISPR-like Defense System

crispr mimivire aix nature virus synbio biotech

MIMIVIRE is the name French researchers have given to the immunity mechanism of mimivirus, and that they have now described in a new paper for Nature.

mimivire_mimivirus_crispr_virophage_nature_aixWhat is a mimivirus? What is viral immunity? What is life? What is CRISPR?

Well, for the last question, you should read our review on CRISPR. As for the rest, you might look for the answer in some of the latest research covered by well-known journal Nature.

Researchers of Aix-Marseille University (France) have published an interesting study on a type of virus called mimivirus.

They have a diameter of about 0.5 mm (enough to be seen with an optical microscope) and the size of their genomes is comparable to bacteria: physical characteristics you really wouldn’t expect from typical viruses.

Also unlike most virus types, they can code amino acids and nucleotides (proteins and DNA building blocks). So they seem to be somewhere between regular viruses and bacteria.

Didier Raoult, one of the authors, defends that mimivirus are alive. In fact, he argues they are a fourth domain of life (but other scientists don’t agree). This theory was spurred by the fact these mimivirus can be infected by other viruses (virophages, similar to bacteriophages that infect bacteria) – like a living organism.

(CC 3.0: Invader Xan)

So what did they discover?

With the ‘Live-or-not’ debate aside, the key finding in this paper is that a certain virophage is able to infect some mimiviruses and use them as a host, but not others. So, these giant virus have evolved a sort of immunity system, in a similar way to which bacteria have developed CRISPR to attack infecting phages and chop them up.

The resistant mimiviruses included sections of the attacking phage’s genetic material in its own genome. Not only that, these sections were located next to genes coding for enzymes which break down DNA. This is another parallel to how CRISPR works, whereby genetic material of previous infections (or attempted infection) are ‘remembered’ by the Host defense system.

Fig 1: Comparison of MIMIVIRE and CRISPR. The mimivirus has a sequence of 28 nucleotides that matches the genes of Zamilon, a virophage.

Researchers still need to understand the precise mechanism of this viral immunity, but they are confident that will hold a lot of answers in the biology field. For example, the origin of these viruses – and perhaps even help the debate on whether viruses can be considered a part of the Tree of Life?

And not only that, but there is a lot of curiosity regarding potential technological applications of this new system. CRISPR was described only some years ago and is already hailed as the key biotechnology discovery of the century.

So will MIMIVIRE be the a second CRISPR, something completely different…or just a textbook curiosity?  

Feature image credit: © Sergey Nivens (BigStock ID98726111)
Figure 1 credit: Levasseur et. al (2016) MIMIVIRE is a defence system in mimivirus that confers resistance to virophage. Nature (doi: 10.1038/nature17146)


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