Bacteria are considered microscopic isolated cells or colonies. They are single microscopic cells with DNA free-floating in their cytoplasm. The size of the bacterial cells varies in size from 2 micrometers to the highest 750 micrometers.
In a recent study, researchers have discovered a bacterium that challenges the prevailing view of bacterial cell size. The bacterium named Thiomargarita Magnifica is the largest bacterium discovered yet. This bacterium is almost 50 times larger than all other known bacteria and can easily be visible to the naked eye. Its complex structure challenges existing notions of bacterial cells. This bacterium is discovered on sunken leaves in the waters of a Caribbean mangrove swamp.
“This discovery adds to the group of large sulfur bacteria and helps to solve the puzzle of what factors limit cell size,” writes Petra Anne Levin in a related Perspective.
Single-cell bacteria, however, often show a surprising range of diversity when in a group.
In this study, Jean-Marie Volland et al. add to this diversity by reporting the discovery and characterization of a sulfur-oxidizing bacterium that can grow orders of magnitude over theoretical limits for bacterial cell size, with a complex membrane organization that likely allowed it to grow to such size, circumventing typical biophysical and bioenergetic limitations.
The organism was first discovered growing as thin white filaments on the surfaces of decaying mangrove leaves in shallow tropical marine mangrove swamps in Guadeloupe, Lesser Antilles.
With the help of various techniques, Volland and colleagues aimed to find out its characteristics. As bacteria are visible only with a compound microscope, with a magnifying capacity of 100 to 1,000 times, this particular bacteria has a length of almost 1 centimeter, which is very easily visible to the naked eye.
Its DNA is compartmentalized within membrane-bound structures, an innovation characteristic of more complex cells, unlike another bacterium with DNA freely floating inside the cell.
The authors’ analyses show that these membrane-bound compartments are metabolically active, with activity occurring throughout the bacterium cell length, as opposed to just at its growing tip.
It is possible that this unique spatial organization and bioenergetic membrane system, which indicate a gain of complexity in the Thiomargarita lineage, may have allowed T. Magnifica to overcome size- and volume-related limitations typically associated with bacteria.
Why do these organisms need to be so large? It is an open question, says Levin.
Levin suggested that it is unlikely that T. Magnifica represents the upper limit of bacterial cell size.
“We really should not underestimate evolution, because we can’t guess where it’s going to go,” says Levin. “I would not have guessed this thing exists, but now that I see it, I can see the logic in the evolution to this point.”
The discovery suggests that large and more complex bacteria may be hiding in plain sight.
- Jean-Marie Volland, Silvina Gonzalez-Rizzo, Olivier Gros, Tomáš Tyml, Natalia Ivanova, Frederik Schulz, Danielle Goudeau, Nathalie H. Elisabeth Nandita Nathdaniel Udwary, Rex R. Malmstrom, Chantal Guidi-Rontani, Susanne Bolte-Kluge, Karen M. Davies Maïtena R. Jean, Jean-Louis Mansot, Nigel J. Mouncey, Esther R. Angert, Tanja Woyke and Shailesh V. Date. A centimeter-long bacterium with DNA contained in metabolically active, membrane-bound organelles. Science, 23 Jun 2022, Vol 376, Issue 6600, pp. 1453-1458 DOI: 10.1126/science.abb36