« Science Brief Today: Water Bears | Main | Child Genius »
Tuesday
Mar292011

Virus-Killers: Are virophages alive?

I had highlighted in a previous post about drilling 4,000 meters down into Lake Vostok in Antarctica – and how exciting it will be to find microbes & more in a lake that has been closed off for millions of years… but today this is exciting news about a surface lake, Organic Lake, in eastern Antarctica and the weird creatures it harbors. Extremophile scientists have been capitalizing on now cheap cheap cheap sequencing techniques (metaproteogenomic analysis) where you can collect a water samples from lakes, sediment, ocean, etc. and sequence all of the microbes in each sample (you only need one copy of the genome of each organism for this to work). They use this technique to access the diversity in different environments. Using this technique an Australian research team found a new virophage – a virus that attacks viruses.

In 2008 the first virophage identified was isolated from a water tower in Paris and named Sputnik because it was found along side a giant virus named mamavirus (acting as a satellite virus, get it… Sputnik…). Sputnik contains a mere 21 genes compared to the humongous mamavirus that encodes more than 900 genes. Mamavirus is the second found Acanthamoeba polyphaga mimivirus (AMPV), the largest known viruses, it was named mamavirus because it is slightly bigger than known mimiviruses. Here’s the cool part: when the mamavirus infects an amoeba it uses its 900 protein-encoding genes to build a viral factory for replication that works within the amoeba – Sputnik hijacks this factory and uses it to replicate, therefore lowering the replication of the mamavirus particles making the virus less infective.


Pictured is immunofluorescence labeling of an amoeba (A. castellannii) infected with a mixture of mamavirus and Sputnik. Red – mamavirus, Green – Sputnik, Blue – nucleic acids (DAPI). A) Sputnik virions entering cytoplasm 30 minutes after infection. B) 4 hours after infection, the first viral factories were seen as distinct, stongly stained patches (Red/yellow). C) 6 hours after infection the viral factories expanded and were strongly stained with DAPI (blue = DNA, because of viral replication). D) 8 hours after infection, mamavirus production observed, E) 12 hours after infection. F) 16 hours after infection.

They named Sputnik a virophage because it was acting as a viral parasite, using the machinery already set up by the mamavirus (just like the mamavirus uses the amoeba machinery to replicate – this is very meta). When La Scola et al. looked further into Sputnik’s genome they found that 3 of the 21 genes shared homology with mamavirus proteins! They not only hijack the mamavirus viral factory, but they might have picked up mamavirus viral particles or genes while using its factory. Like a boss.

Skip ahead 3 years… a new virophage is found in Antarctica in Organic Lake, named Organic Lake Virophage (OLV). OLV preys on phycodnaviruses (big viruses) that infect prasinophytes (algae found in Organic Lake). In Organic Lake (and in nearby lake, Ace Lake and two tropical lakes in the Galapagos) phycodnaviruses infect algae with intent to kill & OLV comes to save the day by inhibiting the viral production of phycodnavirsus by hijacking its already set up viral factory in the algae, therefore letting algae live to see another day. They determined that the this new virophage affects the entire microbial community and marine environment by “reducing overall mortality of the host and increasing frequency of blooms during polar summer light periods”. Although Organic Lake isn’t 4,000 meters under ice, it is 6,000 years old and has proven to harbor some pretty amazing biodiversity.

Picture (right) is transmission electron micrographs of negatively stained virus-like particles from Organic Lake. A) Phycodnavirus B) virophage C) bacteriophage (thrown in there to show similarities to the bacteria-specific viruses, bacteriophages).

ResearchBlogging.org

La Scola, B., Desnues, C., Pagnier, I., Robert, C., Barrassi, L., Fournous, G., Merchat, M., Suzan-Monti, M., Forterre, P., Koonin, E., & Raoult, D. (2008). The virophage as a unique parasite of the giant mimivirus Nature, 455 (7209), 100-104 DOI: 10.1038/nature07218

Sheree Yau, Federico M. Lauro, Matthew Z. DeMaere, Mark V. Brown, Torsten Thomas, Mark J. Raftery, Cynthia Andrews-Pfannkoch, Matthew Lewis, Jeffrey M. Hoffman, John A. Gibson, and Ricardo Cavicchioli (2011). Virophage control of antarctic algal host–virus dynamics Proceedings of the National Academy of Sciences of the United States of America (PNAS) : 1018221108

EmailEmail Article to Friend

References (4)

References allow you to track sources for this article, as well as articles that were written in response to this article.

Reader Comments (4)

Sputnik is quite cool! But the authors should realize they aren't first virophage. In fact, the phenomenon had been seen before them, and been termed "satellite phage"

Bacteriophage P4 hijacks phage P2 structural proteins to make a unique capsid for its own DNA (and inhibits the growth of P2 in the process).
http://www.thebacteriophages.org/chapters/0260.htm

These are both, however, further examples of how "all the world's a phage."

March 29, 2011 | Unregistered CommenterAnonymous

Eggcellent, it's not a far-stretch to imagine eukaryotic biologists COMPLETELY ignoring prokaryotic biology. Good to note!

March 29, 2011 | Unregistered CommenterBrooke N.

Are the subfields of biology as separated as the subfields of astronomy?

March 29, 2011 | Unregistered CommenterSarah Scoles

I wouldn't know about the subfields of astronomy, BUT generally you only see what you want to see - some have got their Nature & Science blinders on.

March 29, 2011 | Unregistered CommenterBrooke N.

PostPost a New Comment

Enter your information below to add a new comment.

My response is on my own website »
Author Email (optional):
Author URL (optional):
Post:
 
Some HTML allowed: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <code> <em> <i> <strike> <strong>