There’s a new record for the biggest bacterium – and you don’t need a microscope to see it.
The newly discovered species, Thiomargarita magnifica, is about a centimeter long and its cells are surprisingly complex, researchers in Science reported on June 24.
The bacterial hippopotamus is about the size and shape of a human eyelash, said marine biologist Jean-Marie Woland of the Complex Systems Research Laboratory in Menlo Park, California, at a news conference on June 21. Maximum size of about 2 centimeters, T. magnifica is about 50 times larger than other giant bacteria and about 5,000 times larger than most other medium-sized bacterial species.
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Moreover, while the genetic material of most bacteria floats freely inside the cell, T. magnifica packs its DNA in a sac surrounded by a membrane (SN: 6/22/17). Such a compartment is a hallmark of the larger, more complex cells of eukaryotes, a group of organisms that includes plants and animals.
The study’s co-author, Oliver Gross, a marine biologist at the Université des Antilles Pointe-á-Pitre in Guadeloupe, France, first discovered T. magnifica while collecting water samples in tropical marine mangrove forests in the Lesser Antilles of the Caribbean. At first, he mistaken the long white threads for some kind of eukaryote, Gross told a news conference. But a few years later, genetic analysis showed that the organisms were actually bacteria. A closer look under a microscope revealed the bags of cells containing DNA.
Previous studies have predicted that the overall lack of complexity of bacterial cells means that there is a limit to how large bacteria can grow. But the new discovery “breaks our way of thinking about bacteria,” said Ferran Garcia-Pichel, a microbiologist at Arizona State University in Tempe who was not involved in the study. When it comes to bacteria, people usually think small and simple. But this way of thinking can lead researchers to miss many other bacterial species, says Garcia-Pichel. It’s a bit like thinking that the largest animal that exists is a small frog, but then scientists discover elephants.
It is not yet clear what role T. magnifica plays among mangrove forests. It is also not known why it evolved to such a large extent. One possibility, Woland said, is that the length of centimeters helps cells have access to both oxygen and sulfide, which bacteria need to survive.
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