What is Bacteria?
{{Automatic taxobox | name = Bacteria | fossil_range = {{Long fossil range|4200|0|[[Archean]] or earlier&nbsp;– [[Holocene|present]]}} | image = EscherichiaColi NIAID.jpg | image_caption = [[Scanning electron microscope|Scanning electron micrograph]] of ''[[Escherichia coli]]'' [[bacillus (shape)|rods]] | taxon = Bacteria | authority = [[Carl Woese|Woese]], [[Otto Kandler|Kandler]] & [[Mark Wheelis|Wheelis]], 1990 | subdivision_ranks = Phyla | subdivision = *'''[[Gram positive]]/no [[Bacterial outer membrane|outer membrane]]''' [[Actinobacteria]] (high-[[GC-content|G+C]])<br /> [[Firmicutes]] (low-[[GC-content|G+C]])<br /> [[Tenericutes]] (no [[Cell wall|wall]]) *'''[[Gram negative]]/[[Bacterial outer membrane|outer membrane]] present''' [[Aquificae]]<br/> [[Bacteroidetes]]/[[Fibrobacteres]]–[[Chlorobi]] ([[Sphingobacteria (phylum)|FCB&nbsp;group]])<br/> [[Chlamydiae]]<br/> [[Deinococcus-Thermus]]<br/> [[Fusobacteria]]<br /> [[Gemmatimonadetes]]<br /> [[Nitrospirae]]<br /> [[Planctomycetes]]–[[Verrucomicrobia]]/[[Chlamydiae]] ([[Planctobacteria|PVC&nbsp;group]])<br/> [[Proteobacteria]]<br /> [[Spirochaete]]s<br /> [[Synergistetes]] *'''Unknown/ungrouped''' [[Acidobacteria]]<br /> [[Chloroflexi (phylum)|Chloroflexi]]<br /> [[Chrysiogenetes]]<br /> [[Cyanobacteria]]<br /> [[Deferribacteraceae|Deferribacteres]]<br /> [[Dictyoglomi]]<br /> [[Thermodesulfobacteria]]<br /> [[Thermotogae]] | synonyms = Eubacteria <small>Woese & Fox, 1977</small> }} '''Bacteria''' (singular: '''bacterium''') are very small [[organism]]s. They are [[prokaryotic]] [[microorganisms]]. Bacterial [[cell]]s do not have a [[cell nucleus|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 org