Scientists discover giant bacteria that is visible to the naked eye

27 Jun 2022

A single filament of Thiomargarita magnifica, the largest bacteria discovered to date. Image: Jean-Marie Volland

The centimetre-long Thiomargarita magnifica is larger than any other bacteria discovered to date.

Scientists have discovered a giant bacteria that is roughly 1cm long and the first to be visible with the naked eye, challenging views of the theoretical limits of bacteria growth.

The bacteria, named Thiomargarita magnifica, is around 50 times larger than any other known giant bacteria and is also surprisingly complex.

“It’s 5,000 times bigger than most bacteria,” said Jean-Marie Volland, lead author of the research paper. “To put it into context, it would be like a human encountering another human as tall as Mount Everest.”

The thin white filaments of the bacteria, which are around the size of human eyelashes, were discovered on decaying mangrove leaves in the waters of a shallow tropical marine swamp in Guadeloupe.

They were first found by Olivier Gros, a marine biology professor who was looking for sulfur-oxidising symbionts in the area.

“When I saw them, I thought, ‘Strange,’” Gros said. “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.”

After examining the bacteria, the researchers believe a complex membrane is how the organism managed to grow so large.

Most bacteria have their DNA floating freely inside the cell. However, the DNA of Thiomargarita magnifica is compartmentalised within membrane-bound structures, which is an innovation characteristic of more complex cells.

These membrane-bound compartments are metabolically active, according to the study, with activity occurring throughout the bacterium cell length.

Microbiologist Petra Anne Levin, who was not involved in the paper, said the discovery helps to solve the puzzle “of what factors limit cell size”.

Levin said that it is unclear why these organisms need to be so large in the first place, but added that it is unlikely that Thiomargarita magnifica represents the upper limit of bacteria. This view is shared by the study authors, who said that large and more complex bacteria “may be hiding in plain sight”.

“Bacteria are endlessly adaptable and always surprising – and should never be underestimated,” Levin said.

10 things you need to know direct to your inbox every weekday. Sign up for the Daily Brief, Silicon Republic’s digest of essential sci-tech news.

Leigh Mc Gowran is a journalist with Silicon Republic