Bacteria are usually organisms that are so small that they can only be seen through a microscope. However, scientists just found the world's largest bacterium in a mangrove swamp in the Caribbean.
Marine biologists found it lurking on rotting leaves in the brackish waters of a red mangrove swamp in Guadeloupe in the Lesser Antilles. The bacterium was so large that it could be easily seen with the naked eye. Also, it is a long, filamentous microbe with a more complex structure and stores its DNA in little packets, unlike most bacteria, Science Alert reported.
This illustration depicted a three-dimensional (3D), computer-generated image, of a group of Gram-positive, Streptococcus pneumoniae bacteria. The artistic recreation was based upon scanning electron microscopic (SEM) imagery.
The Mount Everest of Bacteria
Researchers named the new species Thiomargarita magnifica. It is 5,000 times larger than most bacteria and 50 times bigger than all known giant bacteria. California-based marine biologist Jean-Marie Volland, who also works as the lead author of the study, said that the new bacteria is like a human encountering another human who is as big as Mount Everest.
Researchers have discovered a bacterium—named Thiomargarita magnifica—that challenges the prevailing view of bacterial cell size. It is larger than all other known giant bacteria by ~50-fold. Learn more: https://t.co/bvUSuR2ebK #ScienceResearch pic.twitter.com/RC8YWm4sVA
— Science Magazine (@ScienceMagazine) June 23, 2022
According to a press release via Berkeley Lab, the world's largest bacterium was first discovered in 2009 by marine biology professor Olivier Gros of the Université des Antilles in Guadeloupe. His research focused on the marine mangrove system and he was looking for sulfur-oxidizing symbionts when he first encountered T. magnifica.
He recalled seeing it for the first time and was in awe after realizing it was a bacterium. He conducted microscopy studies over the next couple of years and found that it was a sulfur-oxidizing prokaryote, which somehow changes their view of single-celled organisms.
Study co-first author Silvina Gonzalez-Rizzo, an associate professor of molecular biology at the same university, performed 16S rRNA gene sequencing to classify what kind of prokaryote it was. She also did not expect it to be a bacteria, but results showed that it was indeed a single cell that they refer to as a "macro" microbe.
T. magnifica Has Unique Placement of Organelles
Researchers also found in their analysis that T. magnifica has unique placements of its organelles, Inverse reported. They expected its DNA, membranes, and ribosomes to spread out across the cell since most bacteria have their DNA typically floating freely inside of them. Only complex organisms, like animals, keep their DNA bound inside cell structures.
But using a dye and molecular tools to illuminate the insides of the bacterium, they found that the bacterium's DNA, and ribosomes, are clustered together in tiny pockets surrounded by a membrane. Volland says that it was not something they expected to find, which took them some time to understand what they were looking at.
Further tests eliminated other possibilities and were left with the conclusion that these cell structures are responsible for replicating the bacteria's genome. They call them "pepins," which are translated to "seeds" in French because they look like seeds of watermelon or kiwi.
They discussed the full findings of their study in the paper titled "A Centimeter-Long Bacterium With DNA Contained in Metabolically Active, Membrane-Bound Organelles," published in Science.
Watch the video video about how the researchers discovered the world's largest bacterium.
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