Jun 25, 2022 - Science

Scientists discover world's largest known bacteria

Filaments of Thiomargarita magnifica.

Filaments of Thiomargarita magnifica. Image: Olivier Gros/Université des Antilles in Guadeloupe

A single cell the size of a human eyelash is now the world's largest known bacteria, scientists report this week.

The big picture: The discovery challenges theories about how big bacteria can be.

  • "It would be like a human encountering another human as tall as Mount Everest," Jean-Marie Volland, a researcher at Lawrence Berkeley National Laboratory (LBNL) and a co-author of the new study said in a news briefing.

Details: Thiomargarita magnifica is 50 times larger than other known giant bacteria and can be seen with the naked eye.

  • Marine biologist Olivier Gros of the Université des Antilles in Guadeloupe discovered the nearly centimeter-long bacterium attached to sunken mangrove leaves. It was first reported in a preprint paper earlier this year and is described in more detail in a paper published today in the journal Science.
  • The bacterium has more than 500,000 copies of its genome (which has three times as many genes as most other bacteria) in a single cell. With six terabytes of DNA, the bacterium stores 1,000 times more DNA than a human cell, said co-author Tanja Woyke of LBNL.
  • Unlike other bacteria in which DNA floats around the cell, the bacterium's DNA is encapsulated in compartments in the cells — an unusual degree of complexity for bacteria.
  • The researchers suggest the DNA is compartmentalized because the bacterium has to have multiple copies of its genome to produce the proteins it needs throughout its giant structure.

The intrigue: The giant cells aren't fragile.

  • It is "actually quite puzzling to realize that a single bacterium can be so strong and hold its shape like this," Volland said, adding "it is probably the first opportunity we have to play with tweezers with a single bacterium."
  • It's unclear why the bacterium is big. One possibility is it allows them to escape predators.

What they're saying: The complex bacterium isn't the missing link between single-celled prokaryotes and multicellular eukaryotes, the researchers said.

  • "But it has come close to achieving similar kinds of complexity as you would see in eukaryotic cells," co-author Shailesh Date of the Laboratory for Research in Complex Systems said.
  • "The project has opened our eyes to the unexplored microbial diversity that exists. Who knows what interesting things we are yet to discover?"
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