Bacteria

Bacteria Temporal range: Archean or earlier – present Had'n Archean Proterozoic Pha.
Scanning electron micrograph of Escherichia coli rods
Scientific classification
Domain:	Bacteria Woese, Kandler & Wheelis, 1990
Phyla
Gram positive/no outer membrane Actinobacteria (high-G+C) Firmicutes (low-G+C) Tenericutes (no wall) Gram negative/outer membrane present Aquificae Bacteroidetes/Fibrobacteres–Chlorobi (FCB group) Chlamydiae Deinococcus-Thermus Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes–Verrucomicrobia/Chlamydiae (PVC group) Proteobacteria Spirochaetes Synergistetes Unknown/ungrouped Acidobacteria Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Dictyoglomi Thermodesulfobacteria Thermotogae
Synonyms
Eubacteria Woese & Fox, 1977

Bacteria (singular: bacterium) are very small organisms. They are prokaryotic microorganisms.

Bacterial cells do not have a nucleus, and most have no organelles with membranes around them. Most have a cell wall. They do have DNA, and their biochemistry is basically the same as other living things. They are amongst the simplest and the oldest organisms.

Almost all bacteria are so tiny they can only be seen through a microscope. Bacteria are made up of one cell, so they are a kind of unicellular organism. They were one of the earliest forms of life, and are simple single-celled organisms. They include extremophiles, which live in extreme habitats.

There are probably more individual bacteria than any other sort of organism on the planet, except viruses.^[1] Most bacteria live in the ground or in water, but many live inside or on the skin of other organisms, including humans. There are about as many bacterial cells as human cells in our bodies.^[2][3] Some bacteria cause diseases, but others help us in everyday activities like digesting food (gut flora). Some we use in factories to make cheese and yogurt.

The founder of bacteriology was a German biologist called Ferdinand Cohn (1828–1898). He published the first biological classification of bacteria, based on their appearance.^[4]

1. ↑ Cite error: The named reference lots was used but no text was provided for refs named (see the help page).
2. ↑ Crew, Bec (11 April 2018). "Here's how many cells in your body aren't actually human". ScienceAlert. Retrieved 2019-08-07.
3. ↑ Yong, Ed (2016-01-08). "You're probably not mostly microbes". The Atlantic. Retrieved 2019-08-07.
4. ↑ Encyclopedia Britanniaca: Bacteriology