Bacteria, Big Size

Some bacteria are exceptionally large, even visible to the naked eye, with sizes far exceeding typical bacterial dimensions.​

Examples of Big Bacteria

Thiomargarita magnifica is currently the largest known bacterium, with an average length of 1 cm and some reaching up to 2 cm (20,000 μm), rivaling the length of a human eyelash. These bacteria are found on submerged mangrove leaves and are easily seen without a microscope.​

Thiomargarita namibiensis is another giant bacterium, reaching up to 0.75 mm (750 μm) in diameter. This is still hundreds of times larger than typical bacteria, and individual cells may appear as small pearls.​

Epulopiscium fishelsoni lives in the gut of surgeonfish and can exceed 0.5–0.7 mm (up to 700 μm), also visible without magnification.​

Adaptations and Significance

These bacteria overcome the usual size limitations by having unique adaptations. For example, T. magnifica and T. namibiensis have most of their volume taken up by large vacuoles, pushing the cytoplasm and cellular machinery to a thin layer at the periphery of the cell, which allows nutrient exchange to occur efficiently despite their gigantic size.​

Their sizes are thousands of times greater than those of normal bacteria (e.g., E. coli is about 2 μm long), and their existence challenges classical views of what is possible for single-celled organisms.​