Bacteria are single celled organisms that have a cell wall, but lack many of the organelles found in more complex cells. They are found virtually everywhere on Earth and it is estimated that could be as many as a billion different species of bacteria. The best known bacteria are those that cause infections in humans, but most are harmless and some are actually helpful for human health. Bacteria are also well known for their small size, which allows them to take in the required nutrients and expel waste products. The average size of a bacteria is 2 micrometers in length with a diameter of just 0.5 micrometers. Almost all species of bacteria are invisible to the naked eye and a microscope is required to view them. However, at least one species of bacteria is large enough to see with human eyes.
What is the largest living bacteria?
The largest species of bacteria that has been discovered is called Thiomargarita namibiensis. This species can reach a diameter of 0.75 mm (750 micrometers) and at this size are visible to the naked eye. However, the average diameter for this species is 0.1-0.3 mm. It was discovered on the seafloor of the continental shelf near Namibia in 1997 and a closely related strain was found in 2005 in the Gulf of Mexico. The Thiomargarita namibiensis is a member of the Proteobacteria group of bacteria.
The longest, and second largest, bacteria ever discovered is called Epulopiscium fishelsoni which was discovered in 1985 in the intestines of a surgeonfish. It only reaches 0.1 mm in diameter, but can reach 0.7 mm in length (commonly 0.5 mm).
Did you know?
Large bacteria are actually at a significant disadvantage because the surface area of their cell membrane is small in relation to the size of the cell. This means that they would have a lower level of nutrient uptake. However, Thiomargarita namibiensis has large vacuoles that are used for storing the nutrients it requires to live!