The world’s largest bacteria is visible to the naked eye

The new discovery is 50 times bigger than the previous record-holder.
Grant Currin
Close-up images of the new bacteria. Tomas Tyml

The record for the largest bacterium known to science has been shattered to pieces. The newly discovered Thiomargarita magnifica is an astonishing 50 times bigger than the previous record-holder. And that's not all. T. magnifica — first discovered in a mangrove swamp in Guadeloupe, Lesser Antilles — violates a ton of assumptions about microbes.

For one thing, it's not a microbe.

"We are reporting a new species of a giant bacteria... that forms filaments up to 20,000 micrometers long," marine microbiologist Jean-Marie Volland told reporters at a press conference on Tuesday. "They are by far the largest bacteria known today. The average length of a single cell is about one centimeter," he said. T. magnifica is the size and shape of an eyelash "yet it is a single bacterial cell."

Seriously, T. magnifica is huge

It's hard to overstate just how big these bacteria are. Here's one way to think about it. If you were the size of a typical bacterium, encountering T. magnifica would be like coming across someone as tall as Mt. Everest. Of course, someone that tall would have all kinds of problems. Could their heart pump blood a couple of miles up to their head? Could their ankles bear all the weight? 

Researchers have been asking similar questions about other types of "giant" bacteria. It turns out that T. magnifica could provide some answers. In a related article published alongside the new research, cellular biologist Petra Anne Levin explains that "[f]or large cells, the diffusion of molecules is likely a primary challenge." Eukaryotic cells have organelles to speed along important tasks like sending messages and moving materials, but bacteria don't have those tools. She writes that this discovery "helps to solve the puzzle of what factors limit cell size."

A new organelle supports the huge size

Early research on this newly discovered organism has revealed that T. magnifica has developed some unusual anatomy, including a never-before-seen organelle. "Instead of having their DNA floating freely in their cytoplasm, these giant cells have their DNA inside small, membrane-bound compartments," Volland says. "These compartments represent a new type of bacterial organism that we named 'pepins,' which means, in French, the small seeds in fruits," he says.

That's a huge deal — and it breaks a lot of ideas about what makes different types of cells distinctive. "Until now, the packing of a cell's DNA inside of membrane-bound organelles was considered to be strictly limited to the eukaryotic cells, which are the building blocks of organisms such as humans, other animals, or plants," Volland says. "T. magnifica is therefore a fascinating example of a bacterium that has evolved a higher level of complexity." 

And in case you were wondering if T. magnifica poses any threat to humansthe answer is a flat-out no, according to experts who've had a chance to study the organism. 

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