Giant Bacteria: The Brontosaurus of Bacteria

Ulf von Rauchhaupt

Editor in the “Science” section of the Frankfurter Allgemeine Sunday newspaper.

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The stately stature alone makes

something very special: the organism is a good one centimeter long and visible to the naked eye.

This certainly seems remarkable because the life form that researchers working with the French biologist Jean-Marie Volland from the University of California at Berkeley discovered in the mangrove swamps of Guadeloupe is a unicellular organism.

And it's remarkable, but not entirely out of the ordinary either.

There are several marine protozoa that are anything but microbes in the sense of microscopic life, such as the bladder

, also known as "sailor's eyeball" in English, whose cells can reach diameters of up to four centimeters.

But

is not an alga or any other higher creature in a cell-biological sense, but a bacterium.

The largest species of bacteria known to date, the sulfur

, grows to an average length of 180 micrometers, isolated specimens reach a proud 750 micrometers or 0.75 millimeters, for which you then need at least a magnifying glass as a person with normal vision.

As the name suggests,

is related to this now-dethroned record holder, but grows to be 50 times its size, larger than some animals, such as nematodes or fruit flies.

The vast majority of bacteria, on the other hand, do not reach more than a few micrometers.

This towers over

by five thousand times.

"It's like meeting a human being the size of Mount Everest," says Jean-Marie Volland.

A soul of nitrate

was discovered

as an unusual cluster of long white filaments on the surface of decaying leaves in the mangrove swamp of the French Caribbean island.

As Volland and co-authors now report in Science, the macroscopic microbe lives by “breathing” nitrate and oxidizing sulfur in the process.

The name Thiomargarita literally means "sulphur pearl" and comes from the sulfur granules that members of this genus carry in their cytoplasm.

The giant bacilli stores the nitrate in a gigantic sac, or vacuole, that occupies most of its cell, leaving only two to three microns of space beneath the cell membrane for the sulfur granules and other organelles.

solves

the problem of all giant protozoa: how to transport the molecules responsible for metabolism through the enormous dimensions of the cell quickly enough when mere diffusion only allows the biomolecules to move at typical speeds of one millimeter per hour.

Another trick of large protozoa is to distribute the genetic material with the instructions for the synthesis of important biomolecules throughout the cell.

A

cell contains an estimated 40,000 copies of its genetic information and takes the principle of the decentralized genome to the extreme in that it packs each of these sets of DNA individually into its own vesicles, so-called pepins.

Petra Anne Levin of Washington University in St. Louis, in her commentary accompanying the

publication, writes that data indicated that these pepins are key sites for protein synthesis.

"Along with this, the structure of the pepines suggests that they function almost like autonomous organisms within the cell as a whole."

The fascination, but also the mystery, of

is its sheer, unexpected size.

This raises questions similar to those asked by paleontologists in the face of the enormous herbivorous sauropods of the Jurassic and Cretaceous periods: Why - through which evolutionary processes - could or had these bacteria become so large?

And: Have they already reached the upper limit of what can become of bacterial cells in terms of their dimensions and the associated metabolic issues?