World’s Largest Bacterium Discovered in Caribbean Mangrove Swamps

Scientists have identified a macroscopic species of bacterium in the waters of a Caribbean mangrove swamp, changing the size of how big bacteria were thought to be. The new species, Thiomargarita magnifica, meaning “sulfur pearl,” is a huge thin white filament visible to the naked eye.

The bacterium also has a complex membrane organization and a predictable life cycle, reports Gizmodo's Isaac Schultz. Details on the mega bacterium were published this week in Science.

"These bacteria are about 5,000 times larger than most bacteria," marine biologist and lead-author Jean-Marie Volland says in a statement. "To put things into perspective, it is the equivalent for us humans to encounter another human who would be as tall as Mount Everest."

Scientists have not been able to grow the bacteria in lab culture yet. But they have been making discoveries about the bacteria anyway. Inside the gigantic cell, they found an unusual structure. It has a large central compartment, or vacuole. Vacuoles are frequently generalist, multi-functional spaces within cells that contain fluids, waste or collections of enzymes. The vacuole in these cells, however, is strange in that it runs the entire length of the cell and takes up most of the cell’s volume, Christina Larson for the Associated Press reports. "The acquisition of this large central vacuole definitely helps a cell to bypass physical limitations ... on how big a cell can be," says biologist Manuel Campos at the French National Center for Scientific Research, to the Associated Press. He was not involved in the study.

The bacterium, roughly the shape and size of an eyelash, was first discovered in 2009 in the mangrove swamps of Guadeloupe, an island in the Lesser Antilles. The bacteria appeared as long translucent centimeter-long strings on decaying leaf matter in the water, Gizmodo reports. Because of the bacterium's size, scientists initially thought the white strands were eukaryotes. 

After researchers brought samples back to the lab and viewed them under a microscope, they saw that T. magnifica did not have nuclei or mitochondria, organelles typically found in eukaryotic cells. Instead, the team found sulfur granules inside, per Gizmodo. Scientists further analyzed the bacterium's genome of 12 million base pairs and found that it reproduces by constricting one end before the cell splits in two. 

Bacteria are commonly thought to be “bags of enzymes,” where there is no nucleus or Golgi apparatus or any other organelles, and DNA simply floats freely through the cell. However, T. magnifica not only contains DNA within a membrane, but also ribosomes—which create proteins—cohabitating with the genome.

While researchers are unsure why T. magnifica is so big. According to the Associated Press, it may be an adaption to help it avoid being eaten by smaller organisms. Next, the team plans on exploring how the bacterium plays a role in the mangrove ecosystem.

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.