Group: I (dsDNA viruses)
Species genus: Pandoravirus salinus
Description and Significance
Pandoravirus salinus is the largest known virus to date. It is found in the sediments of Chile coastal area by Professor Jean-Michel Claverie and Professor Chantal Abergel. Both of them are evolutionary biologists at the Aix-Marseille University of France . The largest known virus on Earth is classified as Group I virus under the Baltimore Classification. The existence of Pandoravirus salinus hint the unknown parts of the tree of life and also suggest the existence of the fourth domain because only 7% of their genes match those in existing databases . P. salinus might be ignored in the past or classified as bacteria due to their lack of regular geometries. However, with its novel morphological features and genetic code twice the size of Megavirus, pandoraviruses will spark a whole new range of questions to the abiding question of the origins of life on Earth . Therefore, it is important for scientists to further investigate this unique microorganism.
Structure, Metabolism, and Life Cycle
The size of P. salinus is 1 μm long and 0.5 μm across, which is large enough to be observed under a bright field microscope  & . A fascinating fact about the P. salinus is that they have a collection of 2,556 genes in their genome as opposed to the flu which consists of 7 genes and human immunodeficiency virus (HIV) which consists of 9 genes . According to the researchers that discovered the largest known virus off the coast of central Chile, the virus happens to have no morphological or genomic resemblance to any previously defined virus families . Their micrometer-sized ovoid particles contain DNA genomes of at least 2.5 and 1.9 megabases, respectively .
Pandoravirus salinus do not make their own proteins, produce energy via ATP synthesis or reproduce by dividing. However, they contain some of the core genes that are common to other giant viruses. They survive through a typical viral life cycle. Using an electron microscope, the researchers witnessed how Pandoravirus salinus inject themselves to an Amoeba hosts. After entering the host, P. salinus empty their own proteins and DNA into the host, hijack the host's nuclei and produce hundreds of new viral particles. The final stage of the viral life cycle would be to lyse the host cells open .
Ecology and Pathogenesis
It is reported that the virus was isolated from the mouth of Chile's Tunquen River located in central of Chile . Furthermore, another member of the Pandoravirus genus, Pandoravirus dulcius were found in a freshwater pond near Melbourne, Australia . Therefore, their habitat is most likely to be in water. Based on Claverie and Abergel's observation, the Pandoraviruses parasitize amoebas. Thus, it is concluded that the P. salinus infect their host via lytic life cycle. Additionally, the researchers who are responsible for the discovery said that these megaviruses which live underwater, are so far harmless to mankind .
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Page authored by Mei Kuen Tang, student of Mandy Brosnahan, Instructor at the University of Minnesota-Twin Cities, MICB 3301/3303: Biology of Microorganisms.