In a swampy, stinky mangrove forest in the French Caribbean, a strange giant hides among the fallen leaves.
Key points:
- Scientists have found a bacterium that is thousands of times larger than most bacteria
- Their genetic model is stored similarly to more complex organisms
- The discovery challenges the idea that bacteria are simple microbes
It looks more like a noodle noodle than something from The Creature from the Black Lagoon and has an insatiable appetite for sulfur, the material that gives rotten egg gas its unmistakable stench.
Meet Thiomargarita magnifica, the largest bacterium scientists have found to date.
At 1 to 2 centimeters long, this giant microbe is larger than a fruit fly and can be seen with the naked eye, according to research published today in Science.
“It’s about 5,000 times larger than most bacteria,” said lead author Jean-Marie Volland, a microbiologist at Lawrence Berkeley National Laboratory in California.
“It would be the same as meeting a human being the size of Everest.”
A giant hidden from view
This mangrove forest is home to the best known bacteria. (Supplied by: Pierre Yves Pascal)
Discovering the largest known bacterium was the last he had in the mind of Olivier Gros when he hunted microbes in the mangrove forests of Guadeloupe in the French Caribbean nearly two decades ago.
As he collected samples of the murky water, Professor Gros noticed a long white filament clinging to a leaf.
The marine biologist decided he needed to take a closer look and took the hair-like filament to his lab at the University of the West Indies in Guadeloupe and saw it with a microscope.
“It was so big,” Professor Gros said.
“I didn’t think it was a bacterium. I thought they were fungi or something.”
Professor Gros could not see any of the typical cellular characteristics you would find in eukaryotes, the broad group that includes plants, animals, and fungi.
For starters, there were no mitochondria, the energy-producing cellular machines.
There were also no nuclei, the small structures within our cells that contain genetic information.
In contrast, the thread-like organism looked more like a single cell than a chain of hundreds.
“It was a weird thing,” he said.
The bacterium is thousands of times larger than most other bacteria. (Supplied by: Olivier Gros)
But an initial genetic analysis revealed that the foreign organism’s makeup matched Thiomargarita, a genus that includes sulfur-feeding bacteria.
So Professor Gros and his team tentatively named the microbe Thiomargarita magnifica, a look at “magnus,” the Latin word meaning “big.”
Strange inside and out
When Dr. Volland joined the lab a few years later, his heart was determined to study the “macromicrobial” and confirm that it was indeed a bacterium made up of a cell.
The team collected more samples from the mangrove forests of Guadalupe and used a series of powerful microscopy techniques to observe the three-dimensional filaments.
When Dr. Volland and his team zoomed in on these unicellular threads and scanned their entire length, he could not see the segments you would expect to see in a multicellular organism.
He also saw small seed-like compartments that contained the genetic model of the bacterium.
These “cucumbers” were a strange feature, because bacterial DNA normally floats freely inside cells instead of clustering perfectly within cellular containers as happens in humans, plants, and animals.
“This had never been observed before in bacteria,” Dr. Volland said.
“It’s actually something that’s characteristic of complex organisms.”
In most bacteria, DNA floats freely within the cell. (Getty Images: Vitalii Dumma)
These packets of genetic material could have allowed the bacterium to grow to its massive size, said Ashley Franks, an environmental microbiologist at La Trobe University who did not participate in the study.
“I used to think that [bacteria] they were always like a soccer ball and were fitted to a certain size, ”Professor Franks said.
“Everything was mixed in the middle and that’s how you got all the features.”
This was thought to be the reason most bacteria have become small, as growing too much would cause their inner chemistry to fall apart, Professor Franks said.
But because the interior of T. magnifica is relatively organized and somewhat separate, it was able to grow to its enormous size without losing its chemical balance.
“It starts to tell us how it goes from something basic like a bacterium to something much more complex,” Professor Franks said.
A library of genetic possibilities
The team then sequenced the T. magnifica genome using five of the filaments they collected.
The genome itself was huge and contained about 12,000 genes, which is three to four times more than most bacteria, Dr. Volland said.
A large portion of the giant bacterium’s genes also indicated that it stores carbon and depends on sulfur for energy.
The bacterium also contains about 37,000 copies of its genome per millimeter, the largest number of copies ever found in a bacterial cell.
Professor Franks said the wealth of genetic material in T.magnifica offered a tempting new toolbox for designing and designing organisms to create products such as biofuels, pharmaceuticals and food.
“I always think of a genome as a book, and that’s a massive library of 37,000 copies of the book, and you can have different books for different things,” he said.
“You can contain a lot of different copies of information in different genomes and make them turn on and off, depending on what you need.”
More questions than answers
For Dr. Volland, T. magnifica opens up a treasure trove of questions, from how the bacterium evolved to being so large to what its role is in the mangrove ecosystem where it lives.
The discovery also challenges the idea that bacteria are simple organisms that can only be seen under a microscope.
“It tells us that bacteria evolve to a higher level of complexity,” Dr. Volland said.
“It’s actually a pretty unique system to look at, because it can be seen as an opportunity to study the evolution of biological complexity in real time.”
Professor Gros said the next step would be to figure out how to grow giant bacteria in the lab and learn more about their physiology, such as how it binds to fallen mangrove leaves.
“We [will] they have many, many years of experiments with this model, ”he said.
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Posted 14 hours ago 14 hours ago Thu, June 23, 2022 at 6:30 PM, updated 8 hours, 8 hours ago, Friday, June 24, 2022 at 1:08 AM