There are three known domains of life: Bacteria, Archaea, and Eukaryotes.
Now scientists believe they may have discovered a fourth domain—a previously unknown branch of life.
Fox News has reported a study by the French National Research Agency at Aix-Marseille University that has uncovered two large viruses named “Pandoraviruses,” a reference to Pandora, the mythical Greek figure who opened a box and released evil into the world.
Our knowledge of Earth’s microbial biodiversity is still incomplete, says virologist Jean-Michel Claverie, a coauthor of the study, which has been published in this week’s issue of the journal Science.
One of the viruses, Pandoravirus salinus, was unearthed from sediments collected off the coast of Chile. The other, Pandoravirus dulcis, was picked up in a freshwater pond near Melbourne, Australia. (Fox News)
The average virus is about one one-hundredth the size of the average bacterium. Most viruses are too small to be seen directly with an optical microscope. (Wikipedia) Both of the new viruses are big enough to be seen using a traditional light microscope. (Fox News)
The genome of P. salinus is 1.91 million DNA bases long, while that of P. dulcis is 2.47 million DNA bases. The size of the largest viral genome previously encountered, Megavirus chilensis, is 1.18 million bases in length. (Fox News)
A typical flu virus can have as few as 10 genes, and M. chilensis harbors about 1,000 genes. Pandoraviruses have more than 2,000 new genes coding for proteins and enzymes. The purpose of the genes has yet to be determined. (Fox News)
A genome consists of all of the DNA in an organism. The human genome is 3 billion bases long, arranged on 23 pairs of chromosomes. A gene is a piece of genetic material inside the chromosome. Genes are arranged in a line along the DNA molecule. Each gene contains several thousand bases. The sequence of bases in the gene determines the properties of the gene. There are between 30,000 and 40,000 genes in our bodies. (The Human Genome Project)
Proteins make up a large part of each cell. There are an estimated 100,000 different proteins in the human body. (Wikipedia)
Pandoraviruses may expand our knowledge of life on Earth because they represent a fourth domain of microbial organisms. (Fox News)
Three tests are used to determine if an organism is a virus. One is that viruses spawn hundreds of new copies in one cycle, rather than splitting in two, like typical bacterium or cells. The second is that Pandoraviruses lack the genes needed for energy production. Third, viruses cannot produce proteins without infecting single-celled organisms, such as amoebas. An amoeba is a single blobby cell surrounded by a porous membrane. It can live in fresh water, salt water, wet soil, and animals, which makes it conveniently available to viruses. (Enchanted Learning) Amoebas are the viral hosts preferred by Pandoraviruses. (Fox News) Viruses have to rely on living cells in order to multiply.
Pandoraviruses satisfy all three tests for a virus.
Claverie and his team theorize that the ancient ancestors of Pandoraviruses were once free-living cells that gradually lost most of their genes as they became parasitic. (Fox News)
Scientists previously believed that there were three domains of cellular life. The first, bacterium, is a single-celled organism. It is a type of prokaryote, which is the kind of organism that does not possess a distinct nucleus.
The second, archaea, are the largest group of prokaryotes. They are also single-celled organisms, but they can thrive in extreme environmental conditions, which make them extremophiles. (Free Online Dictionary)
A eukaryote is an organism made up of one of more cells with distinct nuclei. Animals and plants fall within this domain. (Fox News) Eukaryotes constitute a very small minority of all living things. The human body has ten times more microbes than Eukaryotes. (Wikipedia)
Pandoraviruses may constitute a fourth domain of life. Their biochemical and regulatory functions may have significant biotechnical and biomedical applications.
By: Tom Ukinski