Bacteria

Antonie van Leeuwenhoek was the first to observe the one celled micro-organisms we call bacteria.^[1] He described observing bacteria using a primitive microscope he made, that were from a sample of the plaque from his own teeth, in a letter to The Royal Society, in 1683.

Bacteria are not the only single-celled micro-organisms. Archaea, like bacteria, lack a cell nucleus and other cell organelles, like mitochondria. Yeast and amoeba are single-celled micro-organisms that have a nucleus.

Bacteria are believed to have first evolved between 3.2 and 3.5 billion years ago -- after archaea, believed to have first evolved between 3.5 and 4 billion years ago -- but before all more complex life

References

↑ Ulrich Kutschera (2023-08-02). "Antonie van Leeuwenhoek (1632–1723): Master of Fleas and Father of Microbiology". National Institute of Health. doi:10.3390/microorganisms11081994. Retrieved 2026-10-07. Much has been written about van Leeuwenhoek’s discovery of bacteria, as documented in his letter of 17 September 1683. In this report to the Royal Society, he described his microscopical observations on the plaque isolated from his own teeth: moving living “little animalcules” (bacteria), and other microorganisms.

[Nih-Leeuwenhoek-2023-08-02-1] Ulrich Kutschera (2023-08-02). "Antonie van Leeuwenhoek (1632–1723): Master of Fleas and Father of Microbiology". National Institute of Health. doi:10.3390/microorganisms11081994. Retrieved 2026-10-07. Much has been written about van Leeuwenhoek’s discovery of bacteria, as documented in his letter of 17 September 1683. In this report to the Royal Society, he described his microscopical observations on the plaque isolated from his own teeth: moving living “little animalcules” (bacteria), and other microorganisms.

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