Largest-known bacterium found in mangrove — and you can see it without a microscope

The hair-like bacteria is larger than a fruit fly.(Supplied: Tomas Tyml)

In a stinky, swampy mangrove forest in the French Caribbean, a strange giant lurks among the fallen leaves.

Key points:

  • Scientists have found a bacterium that is thousands of times larger than most bacteria
  • Its genetic blueprint is stored in a similar way to more complex organisms 
  • The discovery challenges the idea that bacteria are simple microbes

It looks more like a vermicelli noodle than something out of The Creature from the Black Lagoon and it has an insatiable appetite for sulphur — the stuff that gives rotten egg gas its unmistakable stench.

Meet Thiomargarita magnifica, the largest bacterium that scientists have found so far.

At a whopping 1 to 2 centimetres long, this giant microbe is bigger than a fruit fly and can be seen with the naked eye, according to the research published today in Science.

“It’s about 5,000 times bigger than most bacteria,” said lead author Jean-Marie Volland, a microbiologist at the Lawrence Berkeley National Laboratory in California.

Discovering the largest-known bacterium was the last thing on Olivier Gros’s mind when he was hunting for microbes in the mangrove forests of Guadeloupe in the French Caribbean almost two decades ago.

While collecting samples from the murky water, Professor Gros noticed a long white filament clinging onto a leaf.

The marine biologist decided a closer look was in order, and took the hair-like filament back to his lab at the University of the Antilles in Guadeloupe and viewed it under a microscope. 

“It was so huge,” Professor Gros said.

Professor Gros couldn’t see any of the typical cellular features you would find in eukaryotes, the broad group that includes plants, animals and fungi.

For a start, there were no mitochondria — the cellular machines that produce energy.

There were also no nuclei, the tiny structures within our cells that hold genetic information.

Instead, the thread-like organism looked more like a single cell than a chain of hundreds.

“It was just something strange,” he said.

Bizarre inside and out

The bacterium is thousands of times bigger than most other bacteria.(Supplied: Olivier Gros)

When Dr Volland joined the lab a few years later, his heart was set on studying the “macro-microbe” and confirming that it was indeed a bacterium made up of one cell.

The team collected more samples from the mangrove forests in Guadeloupe and used a range of powerful microscopy techniques to look at the filaments in three dimensions.

When Dr Volland and his team zoomed in on these single-celled threads and scanned their entire length, he couldn’t see segments you would expect to see in a multicellular organism.

He also saw tiny seed-like compartments containing the bacterium’s genetic blueprint.

These “pepins” were a bizarre feature, because bacterial DNA typically floats freely inside cells instead of being neatly bundled inside cellular containers as it is in humans, plants and animals.

“This has never been observed in bacteria before,” Dr Volland said.

“It is actually something that is characteristic of complex organisms.”

More questions than answers

For Dr Volland, T. magnifica opens up a treasure trove of questions, from how the bacterium evolved to be so huge to what its role is in the mangrove ecosystem it inhabits. 

The discovery also challenges the idea that bacteria are simple organisms that can only be seen under a microscope.

“It tells us that bacteria do evolve to a higher level of complexity,” Dr Volland said.

Professor Gros said the next step would be to figure out how to grow the giant bacteria in the lab and learn more about its physiology, such as how it attaches itself to fallen mangrove tree leaves.

“We [will] have many, many years of experiments with this model,” he said.

Source: ABC News