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Biggest bacterium ever discovered amazes scientists with its complexity

Image of a rod-like bacterium
A newfound bacterium can grow up to 0.78 inches (2 centimeters) long. This image shows a different bacterium with a similar long, skinny shape to the newly discovered microbe. (Image credit: STEVE GSCHMEISSNER via Getty Images)

Scientists discovered an absolutely massive bacterium that can be seen without the aid of a microscope and lurks among the mangroves of Grande-Terre in the Caribbean, Science magazine reported (opens in new tab).

The single-celled organism can grow up to 0.78 inches (2 centimeters) long and resembles a thin string, according to a report describing the discovery, posted Feb. 18 to the preprint database bioRxiv (opens in new tab). The bacterium carries all its DNA inside a membranous pouch, unlike most bacteria, whose genetic material floats, unbound, within their cells. This feature not only sets the newfound microbe apart from other bacteria, but also distinguishes it from other prokaryotes — a group of organisms with very small, simple cell structures. The group includes organisms found in the Bacteria and Archaea domains. 

In contrast to prokaryotes, eukaryotes, such as animals, plants and fungi, have more complex cells that contain a nucleus and other membrane-bound organelles. The newfound, enormous micobe toes the line between prokaryote and eukaryote in that it carries its DNA in a membrane-bound pouch, and it also carries a second, large pouch full of water, which takes up more than 70% of the cell's total volume, Science reported. 

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This water-filled pouch squishes all the cell's contents up against its outermost edge, which may help life-sustaining molecules diffuse into the cell more easily, while toxins pass easily out, Science reported.

A large, sulfur-eating bacterium in the genus Thiomargarita carries the same kind of water-filled pouch, and based on this similarity, plus a genetic analysis, the researchers concluded that the newfound bacterium might belong to the same genus. They proposed that the humongous microbe be named T. magnifica

The humongous bacterium "could be a missing link in the evolution of complex cells," Kazuhiro Takemoto, a computational biologist at Kyushu Institute of Technology, told Science.

"All too often, bacteria are thought of as small, simple, 'unevolved' life-forms — so-called 'bags of proteins,'" Chris Greening, a microbiologist at Monash University who was not involved in the study, told Science. "But this bacterium shows this couldn't be much further from the truth."

Read more about the expectation-defying microbe in Science (opens in new tab)

Originally published on Live Science. 

Nicoletta Lanese
Staff Writer

Nicoletta Lanese is a staff writer for Live Science covering health and medicine, along with an assortment of biology, animal, environment and climate stories. She holds degrees in neuroscience and dance from the University of Florida and a graduate certificate in science communication from the University of California, Santa Cruz. Her work has appeared in The Scientist Magazine, Science News, The San Jose Mercury News and Mongabay, among other outlets.