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DNA evidence allowed biologists to identify a new type of bacteria

Taxonomy is the system biologists use to name living things. DNA evidence allows us to see how related living things are to one another, verifying (or changing!) the naming system.


Remember “King Phillip came over for good soup?” from biology class? This sentence has helped kids everywhere remember “Kingdom, Phylum, Class, Family, Order, Genus, Species” — one way biologists name and categorize living things. Biologists do this so it is easier to talk about them when conducting research.  Even the most microscopic organisms can be organized into “like” groups so that scientists can understand how they are related. . Taxonomy is the science of naming, describing, and classifying all organisms on Earth, including the ones you can’t see with the naked eye — “microorganisms” like bacteria.

Unfortunately, taxonomic knowledge is far from complete. In the past 250 years of research, scientists have named about 1.78 million species of animals, plants and microorganisms, yet there are still an estimated 5 to 30 million more species to be identified! Of those undiscovered, up to 95% of microorganisms are undescribed. That means we have only identified and described about 5% of all microorganisms that can exist in the world!  

50 years ago, microorganisms called cyanobacteria (incorrectly named “blue-green algae” for a while) were grouped by their shapes, simply by looking at them under a microscope. But now, science has advanced to a point where we can now read their DNA, and the study authors wanted to see if doing that instead could provide a more accurate way to group them.The authors hypothesized that their studies would result in more accurate classification.

The authors collected 26 samples of water, soil, and bone for analysis, from varied cold-weather locations around the globe (Antarctica, the Arctic, Greenland, Sweden, and Germany), each suspected to contain  different types of cyanobacteria in the genus Phormidesmis. They grew Phormidesmis from each sample in the laboratory, and then analyzed each of them using a heavy-duty microscope to characterize their shapes and compare them to known cyanobacterial cells.

DNA is a very long molecule made of four “bases” and the order of those bases is unique for each living thing. The cyanobacteria’s DNA was then extracted and isolated from each sample and the base order for each DNA strand was determined. This is referred to as genome sequencing. The authors sequenced a gene known as the “16S rRNA gene” that is commonly used for classification of bacteria. Those gene sequences were compared to other gene sequences in large public databases of already-identified sequences to see if there was a match. 

Based on these DNA results, the researchers were able to provide better classification of cyanobacteria. They also unexpectedly discovered two new species of cyanobacteria based on visual observations and DNA testing. These new organisms were named Phormidesmis arctica and Phormidesmis communis, and the scientists reclassified one species that was previously in the genus Leptolyngbya to Phormidesmis. This species is now Phormidesmis nigrescens

A new genus was also suggested, Leptodesmis, as the genome is not easily recognizable by its shape and appears to belong to more than one taxonomic group. The importance of properly classifying all life forms gives scientists a better understanding of the interrelationships of these organisms and is the necessary basis for other studies. Humankind must understand the smallest living organisms in order to fully understand all living things.

Study Information

Original study: Review of the genus Phormidesmis (Cyanobacteria) based on environmental, morphological, and molecular data with description of a new genus Leptodesmis

Study was published on: March 6, 2019

Study author(s): Lenka Raabova, Lubomir Kovacik, Josef Elster, & Otakar Strunecky

The study was done at: University of Ss. Cyril and Methodius, Trnava, Slovakia; Comenius University in Bratislava, Slovakia; Academy of Sciences of the Czech Republic, Trebon, Czech Republic; University of South Bohemia, Ceske Budejovice, Czech Republic; The Institute of Technology and Business, Ceske Budejovice, Czech Republic

The study was funded by:

Raw data availability:

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This summary was edited by: Gina Riggio