How big is Largest Bacterium? | Scale of the Universe

Thiomargarita magnifica is a bacterium that grows as thin white threads in a Caribbean mangrove swamp. When scientists described it in 2022, it was the largest bacterium known. Each thread is a single cell, about 9 millimeters (0.35 inches) long on average and up to 2 centimeters (0.8 inches). Unlike almost all other bacteria, it can be seen without a microscope.

Size

Most bacteria are about 2 micrometers long, a micrometer being a thousandth of a millimeter. Before 2022, the largest bacterial cells known reached about 750 micrometers (0.75 millimeters). Cells of a relative, Thiomargarita namibiensis, reach that size and average 180 micrometers. The researchers who described T. magnifica wrote that it dwarfs all other known giant bacteria by about 50 times.

In their study, threads with buds at the tip averaged 9.7 millimeters long, and some reached 20 millimeters. The published paper gives the average cell length as more than 9,000 micrometers, that is, more than 9 millimeters. The researchers imaged whole threads in three dimensions with X-rays and with laser microscopes. They found that each thread was one continuous cell with no walls dividing it, except at the very tip, where it pinches off one to four small daughter cells.

Size comparisons

An average cell is about 4,500 times as long as an E. coli bacterium, which is about 2 micrometers long.
If an E. coli bacterium were enlarged to the height of a person 1.7 meters (5 feet 7 inches) tall, T. magnifica on the same scale would be about 7.7 kilometers (4.8 miles) long. That is most of the height of Mount Everest, 8,849 meters (29,032 feet).
An average cell is about 12 times as long as the largest cells of its relative T. namibiensis.
An average cell is about as long as a green coffee bean, which averages 9.6 millimeters.
The longest cells, 2 centimeters long, are about as long as a U.S. penny is wide.

How one cell grows so large

Bacteria are expected to stay tiny because they move chemicals around inside the cell by diffusion, the slow spreading of molecules, which works well only over a few micrometers. The researchers think the unusual structure of T. magnifica helps it get around some of these limits.

About 73 percent of each cell's volume is a large central sac, called a vacuole. The cytoplasm, the cell's working contents, forms only a thin layer about 3 micrometers thick around the edge. That layer holds many small compartments wrapped in membranes, which contain the cell's DNA and the machinery for making proteins. The researchers named them pepins, after the small seeds in fruits such as watermelon or kiwi.

Compartments like these had not been seen in bacteria before. The cell also carries many copies of its genome, its full set of genes: an estimated 37,000 copies per millimeter, or about 740,000 in a 2-centimeter cell.

Where it lives and how it feeds

The bacterium was found in shallow, salty mangrove swamps on Guadeloupe, an island in the Lesser Antilles in the Caribbean. It grows in clusters of white threads attached to sunken leaves of the red mangrove tree, Rhizophora mangle. The name magnifica refers to its exceptional size.

Its genome is about 12 million base pairs long, a base pair being one rung of the DNA ladder. That is as large as the genome of baker's yeast. It includes many genes for getting energy from sulfur compounds and for building food from carbon dioxide.