E. coli can double its numbers every 20 minutes by splitting in two
Bacteria and archaea reproduce by the simplest method imaginable: copy the DNA, grow, and pinch in half. At body temperature E. coli manages this roughly every 20 minutes, while some strains of the tuberculosis bacterium take nearly 100 hours. Even the mitochondria inside your cells still divide the same bacterial way.
Fission means one entity dividing into two or more parts that each grow into something resembling the original. Binary fission yields two; multiple fission yields more. In prokaryotes the lone circular chromosome is duplicated, and each copy attaches to a different patch of membrane. As the cell lengthens, the copies are pulled apart, a new wall called the septum grows across the middle, and two genetically identical daughters emerge, apart from any random mutations. No spindle apparatus is needed, unlike mitosis and meiosis in eukaryotic cells.
The key organiser is a protein called FtsZ, a relative of the tubulin that builds eukaryotic microtubules. It is thought to be the first protein to arrive at the future division site, where it assembles into a Z ring that marks the dividing plane. Two proteins, MinC and MinD, act as brakes that block ring formation, and MinE lifts that block in the middle of the cell so division happens in the right place. Experiments on L-form bacteria, engineered to lack walls, suggest FtsZ needs a cell wall to function; wall-less cells seem to divide by a budding-like squeezing process instead.
Archaea vary. The Thermoproteota have neither walls nor FtsZ and instead use an early version of the ESCRT-III machinery found in eukaryotes to pinch the membrane. Euryarchaeota rely on FtsZ as bacteria do. Division time equals doubling time for a culture, but growth slows sharply once nutrients or space run short.
Organelles descended from bacteria keep the habit. Mitochondria divide frequently even when the cell is not, helping regulate metabolism, and all chloroplasts, plus some non-animal mitochondria, still use FtsZ. Among single-celled eukaryotes, the plane of splitting varies: Amoeba can divide in any direction, Euglena splits lengthwise, Paramecium across its width, and Ceratium at a slant.
Source: Fission (biology)
