A gigantic bacterium found in a Caribbean mangrove is by far the largest ever discovered, and now scientists think they have figured out how it grew to such enormous size.
This species of bacteria, Thiomargarita magnifica, is 5,000 times larger than most bacteria and 50 times larger than all other known giant bacteria. (The name Magnifica refers to the Latin word for “great” and the French word for “magnificent”.)
“To put it in context, it would be like a human meeting another human as big as Mount Everest,” said a California-based marine biologist. Jean-Marie Volland who was the lead author of the study.
centimeter long T. magnifica was discovered on one of the verdant islands of Guadeloupe back in 2009.
At the time of the discovery, marine biology professor Olivier Gros was looking for bacteria that sulfur used to generate energy.
However, he saw something very strange once he poured his swamp water sample into a petri dish. Thin “vermicelli-like” threads visible to the naked eye drifted above the leaves and earth.
“When I saw them I thought ‘strange’,” he said. “At first I thought it was just something curious, white filaments that must have been attached to something in the sediment like a sheet.”
More than a decade later, several researchers have been peering through microscopes to examine the strange little prokaryotes.
The unusual organism was nudged and nudged using fluorescence, X-rays, electron microscopy and genome sequencing so scientists could confirm it was in fact a gigantic single-celled bacterium .
Reporting their findings in Science Today, the team revealed several curious mechanisms that may explain how the unwieldy bacterium pushes the limits of what is theoretically possible in terms of size.
Unlike larger multicellular organisms – eukaryotes like us which have membrane organelles in their cells like the nucleus – bacteria belong to a group of organisms called prokaryotes, which are traditionally thought to be “uncompartmentalized enzyme bags” without internal membranes to separate genetic material.
T. magnifica bucks this trend by having internal membranes to store DNA and ribosomes.
The researchers decided to call these tiny bacterial organelles “pips” (a reference to the tiny seeds found inside fruits such as watermelon or kiwi).
“Because it separates its genetic material into membrane-bound organelles, T. magnifica challenges our concept of the bacterial cell,” the authors of the study write.
As T. magnifica has more internal membranes to play with, it can distribute the protein machinery that is the energy currency of cells, ATP (adenosine triphosphate).
Other bacteria don’t have internal membranes, so the only place to put the ATP-generating machinery (ATP synthase) is in the cell envelope that encapsulates the entire organism.
Because it is difficult to transport this energy very far, this restriction limits the size of most bacterial cells.
Another limitation of most bacteria is that they must be able to double in size in order to split in two to reproduce.
Unlike other bacteria, T. magnifica simply detaches a small part of itself to create a daughter cell, thus freeing itself from this constraint.
T. magnifica has a much larger genome than other bacteria – 11,788 genes compared to 3,935 genes for the average prokaryote.
Genetic analysis revealed a set of genes for sulfur oxidation and carbon fixation, which suggests that T. magnifica is based on chemoautotrophy (it harvests energy through the oxidation of chemicals).
While “confirmation bias related to viral size prevented the discovery of giants virus for more than a century,” there may be other giant bacteria “hiding in plain sight,” the authors concluded.
This article was published in Science.