The largest bacteria in the world are visible to the naked eye. His name is Thiomargarita magnifica and reaches between 1 and 2 centimeters. It is a species of sulfur-oxidizing chemotrophic filamentous bacterium that was discovered by the French biologist Olivier Gros in the detached leaves of red mangrove trees in the Guadeloupe archipelago in the Lesser Antilles.
Compared to the rest of the bacterium, it has an enormous size which, to get an idea, is as if a person measured it like Everest.
It is considered a bacterium because it meets the definition of a unicellular “micro” organism without a differentiated nucleus. The largest bacterium until its discovery was Thiomargarita namibiensisalthough this does not exceed 750 millimeters.
Today, a French-American team of researchers has sequenced the genome of T. magnifica and published it in the journal Science.
In addition to its size, its unprecedented DNA distribution has captured the attention of researchers, further challenging traditional concepts of bacterial cells.
The usual thing, as they point out in SINC, is that a bacterial cell has its DNA free floating in the cytoplasm. However, in T. magnifica it is found in membrane-bound compartments called pips, a characteristic innovation of more complex cells.
These organelles, which also incorporate ribosomes, are metabolically active, according to the authors’ analyses, with activity occurring along the entire length of the bacterial cell, rather than just at its growing tip.
“We know that the pips store the genetic code of the cell. DNA is read and translated into proteins inside of it, and it seems that they are also involved in the production of energy for the cell, but we are far from understanding the full extent of their biochemical functions. “, Volland comments to SINC, “and we don’t know how they form and whether or not they play a role in the giant size of the cell.
In fact, the current status of the largest bacterium in the world is Candidatus (Ca.) Thiomargarita magnifica. The first term is used when a species or genus is well characterized but has not yet been cultivated.
For his part, Volland adds other challenges ahead of us: “Now we have a lot more questions than at the start of the project. We do not know how the general cell structure of this bacterium is maintained. We know that it feeds on sulfur and that it is chemosynthetic, that is to say that it is able to use carbon dioxide to produce complex biomolecules, but we do not know its ecological function, nor where more can be found nor how abundant it is in nature. . »
Another key question is to explain why the cells of Thiomargarita magnifica are so large. “It evolved towards gigantism, which means that being giant gave it a selective advantage, but we don’t know which one and we still don’t have the data to answer this question,” admits the researcher.
“However – he points out – there are certain hypotheses in the scientific community to explain why other large bacteria have become so large. The first is that becoming a giant can be a way of escaping the predator, and in fact , if you become hundreds of times larger than it, you no longer have to worry about it eating you.Another hypothesis is that becoming a long filamentous cell may be advantageous to better exploit the chemical energy available in the body. environment of large sulfur bacteria.
In any case, the authors suspect that the complex organization of its membrane is probably what allowed this bacterium to reach its record size, overcoming the typical biophysical and bioenergetic limitations associated with this type of microorganism.