Everyone who has studied Biology in high school or college has learned about the Linnaean system of classification. This system was developed back in the 1700’s by Carl Linnaeus to create a descriptive hierarchy of species, genus, family, order, class, phylum and kingdom. The system then placed everything living into one of two domains, eukaryotes (which includes animals, plants and fungi) and bacteria. In the 1970’s a third domain was dicovered. Named archaea, the organisms that make up this domain, resemble bacteria. However, unlike bacteria they give off methane as a waste product.
As technology has gotten better, scientists have been able to discover and view smaller and smaller micro-organisms, which leads us to the development of Metagenomics. Metagenomics is the study of metagenomes, which is the genetic material recovered from environmental samples. Traditionally, genome sequencing relies on the ability to clone cultures in a laboratory and then study them, however metagenomics enables studies of organisms that are not easily cultured in a laboratory. It is estimated that up to 97% of living organisms cannot be cultured, so this new technique is very promising to the discovery of new micro-organisms.
Between 2003 and 2007, environmental samples were taken from the Atlantic, Pacific and Indian Ocean by Dr. Craig Venter, who was studying the diversity of micro-organisms in those oceans. Dr. Jonathan Eisen of the University of California, Davis began looking through the data to determine if there could possibly be new domains of life. Dr. Eisen discovered two genes, RecA and RpoB. When Dr. Eisen began the process of tracking the evolutionary relationships between all of the RecA and RpoB genes found in the samples taken by Dr. Venter, it was discovered that one branch did not fit on the existing tree of life. Could it possibly be the fourth domain of living organism? More research and testing needs to be performed to conclusively make that determination.
What does a fourth domain on the tree of life mean to the average person—not much. But, when you look back to the discovery of the third domain back in the 1970’s was not seen as very important. Now these methane producing organisms are now a factor in many scientist’s climate-change calculations. What will this fourth domain, if it exists, mean to the world?