The Largest Bacterium Has Been Found

The biggest known bacteria was discovered in a Caribbean mangrove swamp, and now researchers believe they have discovered how it got to such a massive size.

Thiomargarita magnifica is a species of bacterium that is 50 times bigger than all other known gigantic bacteria and 5,000 times bigger than other bacteria. (The Latin word for "big" and the French term "magnifique" are referenced in the name Magnifica.)

"To put it into context, it would be like a human encountering another human as tall as Mount Everest," according to marine researcher Jean-Marie Volland, the study's primary author from California.

On one of Guadeloupe's beautiful, green islets, the centimeter-long T. magnifica was found back in 2009.

Professor of marine biology Olivier Gros was searching for microorganisms that used sulfur as a source of energy when he made the finding.

But when he poured his sample of swamp water into a petri plate, he saw something quite strange. Over the leaves and the mud, there were tiny, 'vermicelli-like' threads that could be seen with the naked eye.

"When I saw them, I thought, 'strange'," he remarked. "In the beginning I thought it was just something curious, some white filaments that needed to be attached to something in the sediment like a leaf."  

More than ten years later, a number of researchers have examined the odd tiny prokaryotes under microscopes.

Fluorescence, X-rays, electron microscopy, and genome sequencing were used to probe the strange creature in order to prove that it was, in fact, a massive single-cell bacteria.

The scientists published their results in Science today, outlining a number of intriguing methods that could help to explain how the awkward bacterium exceeds the bounds of what is conceivably feasible in terms of size.

Bacteria belong to a group of organisms called prokaryotes, which are traditionally thought of as "uncompartmentalized bags of enzymes" without any internal membranes to separate off genetic material. This is in contrast to larger, multicellular organisms, or eukaryotes like us, which have membrane enclosed organelles in their cells like the nucleus.

T. magnifica buckes that trend by storing DNA and ribosomes inside internal membranes.

These tiny bacterial organelles were given the name "pepins" by the researchers (a reference to the small seeds found inside fruits such as watermelon or kiwi).

"Because it segregates its genetic material in membrane-bound organelles, T. magnifica challenges our concept of a bacterial cell," the authors of the research claim.

T. magnifica can disperse the protein machines that produce ATP, the cellular energy currency, since it has more internal membranes to work with (adenosine triphosphate).

Since other bacteria lack internal membranes, the sole location for ATP synthase is in the cell envelope that surrounds the entire organism.

This constraint restricts the growth of most bacterial cells since it is difficult to transmit this energy very far.

The requirement for most bacteria to be able to double in volume in order to divide in two to reproduce is another restriction.

T. magnifica, unlike other bacteria, simply separates a little section of itself to produce a daughter cell, circumventing this restriction.

T. magnifica's genome is substantially bigger than that of other bacteria; it has 11,788 genes as opposed to the typical prokaryote's 3,935 genes.

A group of genes for sulfur oxidation and carbon fixation were discovered by genomic research, suggesting that T. magnifica relies on chemoautotrophy (it harvests energy through the oxidation of chemicals).

While "confirmation bias related to viral size prevented the discovery of giant viruses for more than a century" the scientists speculated that there may also be giant bacteria "hiding in plain sight."

This paper was published in Science.