World’s largest bacteria discovered: it can be seen with the naked eye

Scientists have discovered the world’s largest bacteria in a swamp in the Caribbean. Unlike most, it is not microscopic and can be seen with the naked eye.

The thin white filament, about the size of a human eyelash, is “by far the largest bacterium known to date,” said Jean-Marie Volland, a marine biologist at Lawrence Berkeley National Laboratory and co-author of a paper in which the discovery was made.

Olivier Gros, co-author and biologist at the University of the French West Indies and Guyana, found the first specimen of this bacterium – called Thiomargarita magnifica , or “magnificent sulfur pearl” – clinging to submerged leaves in the Guadeloupe archipelago, in the Caribbean Sea, in 2009.

The scientist did not immediately identify that this was a bacterium, due to its surprisingly large size, on average, a length of 0.9 centimetres.

Only later genetic analysis revealed that the organism was a single bacterial cell.

“It’s an incredible discovery. It opens up the question of how many of these giant bacteria there are in the world and reminds us not to underestimate bacteria,” said Petra Levin, a microbiologist at the University of Washington, who was not involved in the study.

Olivier Gros also found the bacteria attached to oyster shells, rocks and glass bottles in the Guadeloupe swamp.

Scientists have not yet been able to grow it in the laboratory, but researchers say the cell has an unusual structure for bacteria.

The fundamental difference is that it has a large central compartment, or vacuole (cavity of a cell’s protoplasm), which allows some cellular functions to take place in this controlled environment, rather than throughout the cell.

“Acquiring this large central vacuole definitely helps a cell get around the physical limitations on the size of a cell,” said Manuel Campos, a biologist at the French National Center for Scientific Research, who was not involved in the study.

The researchers also noted that they are not sure why the bacterium is so large, but co-author Jean-Marie Volland has hypothesized that it could be an adaptation, to help it avoid being eaten by smaller organisms.