A newly discovered species of bacteria is the largest ever observed by an absolutely colossal margin, according to a new study published in Science. The single-celled bacterial cell is so big it’s comparable in size and shape to a centimeter-long human eyelash, approximately 5,000 times larger than most other known bacteria. 

“To put things in perspective, it is the equivalent for humans to encounter another human that who would be as tall as Mount Everest,” said Jean-Marie Volland, first study author and marine biologist from Lawrence Berkeley National Laboratory, in a press conference. 

“Of course, that was quite a surprise,” he added. 

Named Thiomargarita magnifica, this unbelievably big bacterium was first discovered by Olivier Gros, a marine biology professor at the Université des Antilles in Guadeloupe, while trawling through the waters of a Caribbean mangrove swamp. 

Due to its huge size, he first assumed it was a eukaryote, the type of cells that animals and plants are made up of. However, when viewed under a powerful microscope, he noticed it lacked the classic hallmarks of a eukaryotic cell, namely a clearly defined nucleus and mitochondria. Further prying revealed that this was, much to his surprise, a bacterium.

Since discovering the strange filament-like bacteria, Gros has found them in the mangroves attached to leaves, oyster shells, glass bottles, and even plastic bags. 

Most bacterial cells are microscopic, typically around two micrometers in length. Some "giant bacteria" can be a few hundred micrometers, a size that scientists have previously believed to be the theoretical maximum for the size of a bacteria. However, this new species shatters that theoretical maximum, measuring 20,000 micrometers, or 2 centimeters, about as wide as your thumb.

Many things about these bacteria are deeply weird. Bacteria typically have their DNA floating freely within the cytoplasm of their cells, but these giant bacteria take a more organized approach, holding multiple genome copies throughout the whole cell within structures that feature a membrane.

They're also as tough as nails. The scientists are able to pick up the lash-sized cells and play around with them without concern they're going to break – a quality the researchers described as “puzzling.”

On top of this, it reproduces in an unusual way. The filament constricts and eventually separates to form a bud containing the DNA. This bud is then “pinched” off and falls into the environment.   

Despite their intimidating size, however, they don’t appear to pose any risk to humans. 

“They are not pathogens for humans. I don’t think we have any problems with humans,“ remarked Gros. 

Since T. magnifica challenges much of what we know about bacteria, the scientists were keen to dive into its genomic complexity. DNA analysis showed that it had three times more genes than most bacteria. Interestingly, it also had duplicates of genes that code for elongation genes and lacked some self-division genes.

However, it isn’t clear when the giant diverged from other members of the genus. It’s also uncertain why the bacteria evolved these bizarre characteristics, but the team has begun to loosely speculate on the possible advantages of becoming a giant.

One idea is that it helps avoid predation. “If you become 100,000 times bigger than your predecessors, you can’t be consumed by your predecessors,” Volland explained.

Another prime theory is its vast elongated shape helps the bacteria to obtain energy. This bacteria uses chemosynthesis to obtain its “food” from hydrogen sulfide found in the mangrove sediment, but it also requires oxygen from water. This elongated shape may help the bacteria “bridge the gap” between the interface between the sulfur-rich sediment and the seawater. 

There are many unknowns that surround T. magnifica. To answer some of these questions, the next step is to cultivate the bacteria in the lab, which has so far proved to be tricky. This bacteria behemoth remains a bit of an enigma for now, but the team is confident that science will unearth more unusual and surprisingly complex bacteria the more we dig into the world of microbes.

“We should look at the evolution of complexity. We have really not explored the microbial world,” concluded Shailesh Date, founder and CEO of the Laboratory for Research in Complex Systems, and one of the article’s senior authors. "[We] might find a whole lot of bacteria that have these amazing morphological features that come closer to what you would see in supposedly higher order forms, like eukaryotes.“