Editing Gram-positive bacteria (section)

=== Exceptions ===
In general, gram-positive bacteria are monoderms and have a single [[lipid bilayer]] whereas gram-negative bacteria are diderms and have two bilayers. Exceptions include:
* Some taxa lack peptidoglycan (such as the class [[Mollicutes]], some members of the [[Rickettsiales]], and the insect-endosymbionts of the [[Enterobacteriales]]) and are [[Gram stain#Gram-variable and gram-indeterminate bacteria|gram-indeterminate]].
* The [[Deinococcota]] have gram-positive stains, although they are structurally similar to gram-negative bacteria with two layers.
* The [[Chloroflexota]] have a single layer, yet (with some exceptions<ref>{{Cite journal |last1=Yabe |first1=S. |last2=Aiba |first2=Y. |last3=Sakai |first3=Y. |last4=Hazaka |first4=M. |last5=Yokota |first5=A. |date=2010 |title=''Thermogemmatispora onikobensis'' gen. nov., sp. nov. And ''Thermogemmatispora foliorum'' sp. nov., isolated from fallen leaves on geothermal soils, and description of Thermogemmatisporaceae fam. nov. and Thermogemmatisporales ord. Nov. Within the class Ktedonobacteria |journal=International Journal of Systematic and Evolutionary Microbiology |volume=61 |issue=4 |pages=903–910 |doi=10.1099/ijs.0.024877-0 |pmid=20495028 |doi-access=free}}</ref>) stain negative.<ref>{{Cite journal |last=Sutcliffe |first=I.C. |date=2011 |title=Cell envelope architecture in the Chloroflexi: A shifting frontline in a phylogenetic turf war |journal=Environmental Microbiology |volume=13 |issue=2 |pages=279–282 |bibcode=2011EnvMi..13..279S |doi=10.1111/j.1462-2920.2010.02339.x |pmid=20860732}}</ref> Two related phyla to the Chloroflexi, the [[TM7]] clade and the Ktedonobacteria, are also monoderms.<ref name="TM7">{{Cite journal |last1=Hugenholtz |first1=P. |last2=Tyson |first2=G.W. |last3=Webb |first3=R.I. |last4=Wagner |first4=A.M. |last5=Blackall |first5=L.L. |date=2001 |title=Investigation of Candidate Division TM7, a Recently Recognized Major Lineage of the Domain Bacteria with No Known Pure-Culture Representatives |journal=Applied and Environmental Microbiology |volume=67 |issue=1 |pages=411–419 |bibcode=2001ApEnM..67..411H |doi=10.1128/AEM.67.1.411-419.2001 |pmc=92593 |pmid=11133473}}</ref><ref name="Kt">{{Cite journal |last1=Cavaletti |first1=L. |last2=Monciardini |first2=P. |last3=Bamonte |first3=R. |last4=Schumann |first4=P. |last5=Rohde |first5=M. |last6=Sosio |first6=M. |last7=Donadio |first7=S. |date=2006 |title=New Lineage of Filamentous, Spore-Forming, Gram-Positive Bacteria from Soil |journal=Applied and Environmental Microbiology |volume=72 |issue=6 |pages=4360–4369 |bibcode=2006ApEnM..72.4360C |doi=10.1128/AEM.00132-06 |pmc=1489649 |pmid=16751552}}</ref>

Some Bacillota species are not gram-positive. The class Negativicutes, which includes ''[[Selenomonas]]'', are diderm and stain gram-negative.<ref name="pmid19667386" /> Additionally, a number of bacterial taxa (viz. [[Negativicutes]], [[Fusobacteriota]], [[Synergistota]], and [[Elusimicrobiota]]) that are either part of the phylum Bacillota or branch in its proximity are found to possess a diderm cell structure.<ref name="Sutcliffe, 2010" /><ref name="Gupta C" /><ref name="pmid19667386" /> However, a conserved signature indel (CSI) in the [[HSP60]] ([[GroEL]]) protein distinguishes all traditional phyla of gram-negative bacteria (e.g., [[Pseudomonadota]], [[Aquificota]], [[Chlamydiota]], [[Bacteroidota]], [[Chlorobiota]], "[[Cyanobacteria]]", [[Fibrobacterota]], [[Verrucomicrobiota]], [[Planctomycetota]], [[Spirochaetota]], [[Acidobacteriota]], etc.) from these other atypical diderm bacteria, as well as other phyla of monoderm bacteria (e.g., [[Actinomycetota]], [[Bacillota]], [[Thermotogota]], [[Chloroflexota]], etc.).<ref name="Gupta C" /> The presence of this CSI in all sequenced species of conventional LPS ([[lipopolysaccharide]])-containing gram-negative bacterial phyla provides evidence that these phyla of bacteria form a monophyletic clade and that no loss of the outer membrane from any species from this group has occurred.<ref name="Gupta C" />