The 'Mount Everest' of bacteria discovered in Caribbean swamps

WASHINGTON • The largest-known bacterium - a vermicelli-shaped organism that was discovered in shallow mangrove swamps in the Caribbean and is big enough to be seen with the naked eye - is redefining what is possible for bacteria, earth's most ancient life form.

Scientists said on Thursday the bacterium, called Thiomargarita magnifica, is noteworthy not merely for its size - colossal for a single-celled organism at up to about 2cm long - but also because its internal architecture is unlike other bacteria.

The DNA, an organism's blueprint, is not free-floating inside the cell like in most bacteria but contained within numerous small membrane-bound sacs. Membrane-bound structures in cells are called organelles.

"It is thousands of times larger than regular-sized bacteria. Discovering this bacterium is like encountering a human being as tall as Mount Everest," said marine biologist Jean-Marie Volland of the US Department of Energy's Joint Genome Institute and the Laboratory for Research in Complex Systems in California, a co-leader of the study published in the journal Science.

The bacterium has been found in several locations in Guadeloupe, a French archipelago in the Caribbean.

It was first spotted in the sulphur-rich seawater of a Guadeloupe swamp by Universite des Antilles microbiologist and study co-leader Olivier Gros.

"In 2009, I found long white filaments attached to a sunken leaf of a mangrove tree. I found such filaments intriguing. I brought them back to the lab to analyse them," Professor Gros said. "Big surprise for me to have so huge a bacterium living in the mangroves of Guadeloupe."

A normal bacterial species measures 1 to 5 micrometres long. This species averages 10,000 micrometres long, with some Thiomargarita magnifica twice that length.

"It is orders of magnitude bigger than what we thought was the maximum possible size for a single bacterium," Dr Volland said.

"They are about the same size and shape of an eyelash."

The largest-known bacterium until now had a maximum length of around 750 micrometres.

Bacteria are single-celled organisms that reside nearly everywhere on the planet, vital to its ecosystems and most living things.

Bacteria are thought to have been the first organisms to inhabit earth and remain quite simple in structure billions of years later.

The bodies of people are teeming with bacteria, only a relatively small number of which cause disease.

Thiomargarita magnifica is not the largest-known single-celled organism. That honour goes to the aquatic alga Caulerpa taxifolia, reaching 15 to 30cm long.

REUTERS