They are usually beings of microscopic scale. But is this true in all cases? Nature can surprise us. It does so with the giant-sized bacterium. It is called Thiomargarita magnifica. This huge bacterium can measure up to two centimeters long and be seen before the human eye.
These bacteria are 5,000 times larger than their peers. They could grow even larger if no external agent damages them. It was first seen 10 years ago in the Grand-Terre mangroves in the Caribbean. It was not known to be a bacterium. Now, a preliminary study by the Kyushu Institute of Technology in Japan has classified it as one.
Traditional science divides organisms into two groups according to their cells. There are prokaryotes (unicellular) and eukaryotes (multicellular). Examples of the former are microbes and bacteria. Examples of the latter are animals, plants and fungi. The DNA of prokaryotes floats freely in their cytoplasm. And eukaryotes package their genome in a nucleus.
But this colossal bacterium is different. “It could be a missing link in the evolution of complex cells,” says Kazuhiro Takemoto. He is a computational biologist who participated in the study.
The single cell of T. magnifica possesses two membrane sacs inside. The inner sac is composed of water and the outer sac, located at the edges of the cell, contains all the DNA. It has 11 million bases harboring 11,000 genes, a number far greater than that of average bacteria.
For the researchers, this particularity of T. magnifica brings them a surprising conclusion. Perhaps the two branches of life (prokaryotic and eukaryotic) are not as different as believed. “Bacteria are thought to be small, simple, ‘unevolved’ life forms. They are so-called ‘protein pockets.’ But such bacteria show that this couldn’t be much further from the truth,” says Chris Greening. He is a microbiologist at Monash University.
The giant-sized bacterium doesn’t just surprise us. It is also about to change the very definition of what a bacterium is. Nature always surprises us.