Pictured: Giant bacteria so big they can be picked up with tweezers

The jumbo species Thiomargarita magnifica is 50 times larger than usual types but is not thought to be dangerous to humans

Giant bacteria which are so big they can be seen by the naked eye – and even picked up with tweezers – have been found by scientists in a discovery which rewrites biology.

The jumbo species Thiomargarita magnificawas found in the marine mangrove swamps of Guadeloupe, in the Caribbean, and is 50 times larger than even the biggest bacteria.

T.magnifica seen against the perspective of a small coin Credit: Tomas Tyml

Researchers say it is so big in comparison to most bacteria that it would be the equivalent of a human finding another human who was as tall as Everest.

Until now, bacteria were always thought to be microorganisms which could only grow to a tiny size and only be viewed under a microscope. But the new organism can grow up to 0.4in (1cm) and resembles a small worm.

Dr Jean-Marie Volland, of Lawrence Berkeley National Laboratory, said: “This is two orders of magnitude above what bacteria can theoretically achieve. It would be like encountering another human that is as tall as Mount Everest.

“They are quite puzzling and it’s interesting that a single bacteria this large can hold its shape. We can play with them with tweezers and remove them from the water. It is fascinating to see how strong it is.

“It tells us we probably are a little bit biased about what bacteria should look like and how complex they should be, when actually there is an incredible diversity and this shows us we should also be looking outside for more examples.”

The enormous bacteria are more complex than usual types but not dangerous to humans Credit: Olivier Gros/Lawrence Berkeley National Labor

Despite its alarming size, T.magnifica is not dangerous to humans, and unlikely to cause any infections except in the immunocompromised.

The enormous bacteria are also more complex than usual types, with their DNA contained in a sac-like structure rather than floating around inside the cell.

Until now, the packing away of DNA in such a way was thought to be the preserve of humans, animals and plants.

Researchers think the unique arrangement may be what allows it to grow to its large size, with experts speculating that it is unlikely T. magnifica represents the upper limit of bacterial cell size.

Despite this, the bacterium is similar genetically to others of its genus although it has more genes linked to elongation.

The bacteria may have evolved to their size in the tropical marine mangrove swamps of Guadeloupe to avoid predators

Scientists are unclear why the species has grown so big but think it may have helped it to survive in the mixed salt water and fresh water of its estuarine environment. It may also have helped it avoid being killed.

Dr Shailesh Date, of the Laboratory for Research in Complex Systems, University of California San Francisco, said: “This has opened our eyes to the unexplored microbial diversity that exists and the origin and evolution of complexity in biological systems

“We don’t know why or how it evolved towards these giant sizes. If you grow hundreds or thousands of times bigger than your predator then you cannot be consumed by your predator. So it could be to escape predation.”

The organism was first discovered growing as thin white filaments on the surfaces of decaying mangrove leaves in shallow waters.

The research was published in the journal Science.