Editing Gram-negative bacteria (section)

== Classification ==
Along with cell shape, [[Gram stain]]ing is a rapid diagnostic tool and once was used to group species at the subdivision of Bacteria.
[[Bacterial taxonomy#History|Historically]], the kingdom [[Monera]] was divided into four [[Taxonomic rank|divisions]] based on Gram staining: [[Bacillota|Firmicutes]] (+), [[Gracilicutes|Gracillicutes]] (−), [[Mollicutes]] (0) and [[Methanogen|Mendocutes]] (var.).<ref>{{cite journal |last1=Gibbons |first1=N. E. |last2=Murray |first2=R. G. E. |title=Proposals Concerning the Higher Taxa of Bacteria |journal=International Journal of Systematic Bacteriology |year=1978 |volume=28 |issue=1 |pages=1–6 |doi=10.1099/00207713-28-1-1 |doi-access=free }}</ref>
Since 1987, the [[monophyly]] of the gram-negative bacteria has been [[Proof (truth)|disproven]] with [[Molecular phylogenetics|molecular studies]].<ref name="woese87">{{cite journal | author = Woese CR | title = Bacterial evolution | journal = Microbiol. Rev. | volume = 51 | issue = 2 | pages = 221–71 |date=June 1987 | pmid = 2439888 | pmc = 373105 | doi =  10.1128/MMBR.51.2.221-271.1987}}</ref>

Current knowledge divides the gram-negatives into two large groups and some straddlers. The more "conventional" gram-negatives with an LPS outer membrane do share a common ancestor and are grouped in kingdom [[Pseudomonadati]].<ref name="valid-dom-kingdom"/> The less conventional ones are, as mentioned above, the order [[Mycobacteriales]], have a [[mycolic acid]] cell wall and an outer membrane.<ref name=Gupta19myc/> The kingdom and the order are each monophyletic (or rather, not holyphyletic), but the "LPS-diderm" and "mycolic-diderm" groups are not, because some bacteria in the kingdom and the order do not, in fact, stain gram negative. They will be discussed in the next section.