Since the discovery of viruses in 1892, the scientific community has been in constant debate whether viruses are or are not living organisms. A majority of scientists fall on the “not” side of the debate arguing that viruses are just too small to be considered living organisms. This is a valid point; however, recent discoveries may be able to take the issue of size right off the table.
Ten years ago, a research team from the French National Center for Scientific Research in Marseille discovered what until now had been the largest virus known to man, the mimivirus. Mimivirus and its relative, megavirus, can reach the size of some bacteria; tipping the scales at 750 nanometers and 1000 genes, these viruses are roughly 70 times larger than HIV. Now the same research team has unearthed two new viruses that are even bigger!
The team termed them “pandoravirus” for their far-reaching implications on the scientific community; pandoraviruses have very little in common with known viruses: size, shape, replication, and DNA make-up all set these viruses apart. Pandoraviruses can reach one micrometer in length and 2,500 genes. That makes these viruses large enough to see with a light microscope, and it also makes these viruses larger than some intracellular bacteria, such as Rickettsia, and some free living bacteria. Pandoraviruses have an ovoid shape with a pore at one and a three-layered envelope. Normal viruses replicate by creating a capsid (box) then filling it with DNA, but pandoraviruses synthesize the DNA and the capsid simultaneously; the French research team termed this process as “knitting.” Of pandoravirus’ 2500 genes, 93% of them are not recognized by scientists; the genes are not found on any other organism known (i.e. they are alien to us).
The first pandoravirus, Pandoravirus salinus, was found in the Tunquen River in Chile. The next one, Pandoravirus dulcis, was discovered in a pond near Melbourne, Australia. Both viruses were found inside the amoeba Acanthamoeba castellani, though many scientists believe the amoebas are not the definitive host; protozoa are another possibility. Researchers have made assurances that these viruses are not harmful to humans or animals, so do not worry about swimming in these areas. Pandoraviruses seem to like to hang out in the sediment at the bottom of the body of water.
The discovery of these new viruses can have profound impacts on viral knowledge; it can lead scientists to a better understanding of viruses as a whole in hopes of enhancing the fight against these corresponding diseases. No one is ready to definitively say that viruses are living organisms, but you cannot help but wonder if these pandoraviruses are some sort of missing link between viruses and bacteria or some other organism yet to be discovered.
The world is full of things waiting to be discovered. All you have to do is take a closer look at the mud in your local pond.
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