Scientists have found a second even more amazing super sized virus. It truly approaches being something between being a virus and being a life form. What they finally learn from this virus about life forms remains to be seen but it should result in some interesting discoveries.
Newfound Virus is a Giant with Lifelike Properties
Scientists have found the ocean's largest virus.
Fortunately, this microbial monster is a menace only to a particular
Based on the size of its genome, or complete DNA sequence, the
microbe dubbed CroV is the second to be considered a "giant virus."
The only virus with a larger genome lives in fresh water.
CroV's enormous, and surprising, genetic code further blurs
the boundary between viruses and cellular life, according to the researchers
who described it.
CroV is equipped with genes that allow it to repair its genome,
synthesize sugars and even gain more control over the machinery that it hijacks
within the host cells to replicate itself.
"They take over the cell, and they basically run the
cell," said Matthias Fischer, who described CroV for his doctoral
dissertation at the University of British Columbia. He added that the
production of new CroV viruses within an infected cell resembles an assembly line.
Viruses are essentially genetic material
wrapped in a thin protein coat, and they must use the goods of a host in order
to make more of themselves.
Traditionally, viruses were considered nonliving. However, these
discoveries about CroV add more weight to the argument that viruses are alive, Fischer
Big virus, tiny host
Fischer found that CroV's genome contains approximately
730,000 base pairs, the building blocks of DNA. By comparison, the largest
virus on record, Mimivirus,
has a genome of about 1.2 million base pairs. Prior to confirmation in 2003 that
Mimivirus was indeed a virus, the largest known virus had a genome of around 331,000
base pairs, according to Fischer.
Despite its size, CroV is a threat only to the relatively small.
It infects a common, single-celled grazing creature called Cafeteria roenbergensis. In fact, the virus is approximately a
twentieth the size of its host. (For a person who stood 5-foot-6, or 1.7 meters,
this would translate roughly into being infected by
a virus the size of a softball.)
C. roenbergensis's diet of bacteria and
viruses may explain the strange collection of genes possessed by the giant
virus that infects it. Perhaps the oddest of these include the genes that code
for the entire pathway to create a key component to a bacterial outer membrane
CroV may have acquired these genes by picking up DNA from
the remains of a bacterium eaten by a cell the virus later infected, according
to the researchers. Something similar also may have occurred with Mimivirus,
which infects a bacteria-eating amoeba and
also appears to contain genes of bacterial origin. This is a possible
explanation for the origin of 10 to 20 percent of the giant virus genes.
Other genes within CroV are even more mysterious. The
researchers could not recognize 51 percent of the genes they encountered in the
new virus. This is actually a low proportion – about 90 percent of the genes within
certain viruses are unknown, Fischer said.
"Every virus you pull out has a new set of genes that
is unique to this virus, that has never been seen before," he said.
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This makes it unlikely that many viral genes have cellular
origins. It is currently hypothesized that viral genes are ancient, and have
never been part of cellular organisms, he said.