GRAM-NEGATIVE BACTERIA are a group of bacteria that do not retain the crystal violet stain used in the gram-staining method of bacterial differentiation. They are characterized by their cell envelopes , which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane .
* 1 Characteristics * 2 Classification
* 3 Taxonomy
* 3.1 Example species
* 4 Bacterial transformation * 5 Medical treatment * 6 Orthographic note * 7 See also
* 8 References
* 8.1 Notes
* 9 External links
Gram-negative cell wall structure
* An inner cell membrane is present (cytoplasmic) * A thin peptidoglycan layer is present (This is much thicker in gram-positive bacteria ) * Has outer membrane containing lipopolysaccharides (LPS, which consists of lipid A , core polysaccharide, and O antigen ) in its outer leaflet and phospholipids in the inner leaflet * Porins exist in the outer membrane, which act like pores for particular molecules * Between the outer membrane and the cytoplasmic membrane there is a space filled with a concentrated gel-like substance called periplasm * The S-layer is directly attached to the outer membrane rather than to the peptidoglycan * If present, flagella have four supporting rings instead of two * Teichoic acids or lipoteichoic acids are absent * Lipoproteins are attached to the polysaccharide backbone * Some contain Braun\'s lipoprotein , which serves as a link between the outer membrane and the peptidoglycan chain by a covalent bond * Most, with very few exceptions, do not form spores
Along with cell shape, gram-staining is a rapid diagnostic tool and
once was used to group species at the subdivision of Bacteria.
Historically , the kingdom
Monera was divided into four divisions
based on gram-staining: Firmacutes (+), Gracillicutes (−),
Mollicutes (0) and Mendocutes (var.). Since 1987, the monophyly of
the gram-negative bacteria has been disproven with molecular studies .
However some authors, such as
This section MAY BE TOO TECHNICAL FOR MOST READERS TO UNDERSTAND. Please help improve it to make it understandable to non-experts , without removing the technical details. The talk page may contain suggestions. (March 2014) (Learn how and when to remove this template message )
Of these two structurally distinct groups of prokaryotic organisms,
monoderm prokaryotes are indicated to be ancestral. Based upon a
number of different observations including that the gram-positive
bacteria are the major reactors to antibiotics and that gram-negative
bacteria are, in general, resistant to them, it has been proposed that
the outer cell membrane in gram-negative bacteria (diderms) evolved as
a protective mechanism against antibiotic selection pressure. Some
bacteria such as
Deinococcus , which stain gram-positive due to the
presence of a thick peptidoglycan layer, but also possess an outer
cell membrane are suggested as intermediates in the transition between
monoderm (gram-positive) and diderm (gram-negative) bacteria. The
diderm bacteria can also be further differentiated between simple
diderms lacking lipopolysaccharide; the archetypical diderm bacteria,
in which the outer cell membrane contains lipopolysaccharide; and the
diderm bacteria, in which the outer cell membrane is made up of
mycolic acid (e. g.
In addition, a number of bacterial taxa (including
Synergistetes , and
Elusimicrobia ) that are either
part of the phylum
Firmicutes or branches in its proximity are also
found to possess a diderm cell structure. However, a conserved
signature indel (CSI) in the
GroEL ) protein distinguishes all
traditional phyla of gram-negative bacteria (e.g.,
The proteobacteria are a major group of gram-negative bacteria,
Escherichia coli (E. coli),
Medically relevant gram-negative cocci include the four types that
cause a sexually transmitted disease (
Medically relevant gram-negative bacilli include a multitude of
species. Some of them cause primarily respiratory problems (Klebsiella
Legionella pneumophila ,
Transformation is one of three processes for horizontal gene transfer , in which exogenous genetic material passes from bacterium to another, the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact) and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium). In transformation, the genetic material passes through the intervening medium, and uptake is completely dependent on the recipient bacterium.
As of 2014 about 80 species of bacteria were known to be capable of
transformation, about evenly divided between
This section NEEDS ADDITIONAL CITATIONS FOR VERIFICATION . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed. (April 2013) (Learn how and when to remove this template message )
One of the several unique characteristics of gram-negative bacteria is the structure of the bacterial outer membrane . The outer leaflet of this membrane comprises a complex lipopolysaccharide (LPS) whose lipid portion acts as an endotoxin. If gram-negative bacteria enter the circulatory system , the liposaccharide can cause a toxic reaction. This results in fever, an increased respiratory rate, and low blood pressure. This may lead to life-threatening condition of septic shock.
The outer membrane protects the bacteria from several antibiotics , dyes, and detergents that would normally damage either the inner membrane or the cell wall (made of peptidoglycan). The outer membrane provides these bacteria with resistance to lysozyme and penicillin . However, alternative medicinal treatments such as lysozyme with ethylenediaminetetraacetic acid (EDTA) and the antibiotic ampicillin have been developed to combat the protective outer membrane of some pathogenic gram-negative organisms. Other drugs can also be used, significant ones being chloramphenicol , streptomycin , and nalidixic acid . Chloramphenicol is rarely used in the EU due to the association with drug induced pancytopenia .
The pathogenic capability of gram-negative bacteria is often associated with certain components of their membrane, in particular, the LPS. In humans, the presence of LPS triggers an innate immune response , activating the immune system and producing cytokines (hormonal regulators). Inflammation is a common reaction to cytokine production, which can also produce host toxicity. The innate immune response to LPS, however, is not synonymous with pathogenicity, or the ability to cause disease.
* Gram-indeterminate * Lower plants
* This article incorporates public domain material from the NCBI document "Science Primer".
* ^ A B Baron S, Salton MR, Kim KS (1996). "Structure". In Baron S, et al. Baron\'s Medical Microbiology (4th ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1 . PMID 21413343 . * ^ Gibbons, N. E.; Murray, R. G. E. (1978). "Proposals Concerning the Higher Taxa of Bacteria". International Journal of Systematic Bacteriology. 28 (1): 1–6. doi :10.1099/00207713-28-1-1 . * ^ Woese CR (June 1987). "Bacterial evolution" . Microbiol. Rev. 51 (2): 221–71. PMC 373105 . PMID 2439888 . * ^ Cavalier-Smith, T. (2006). "Rooting the tree of life by transition analyses" . Biol. Direct. 1: 19. doi :10.1186/1745-6150-1-19 . PMC 1586193 . PMID 16834776 . * ^ A B C D Gupta RS (December 1998). "Protein phylogenies and signature sequences: A reappraisal of evolutionary relationships among archaebacteria, eubacteria, and eukaryotes" . Microbiol. Mol. Biol. Rev. 62 (4): 1435–91. PMC 98952 . PMID 9841678 . * ^ A B Gupta RS (2000). "The natural evolutionary relationships among prokaryotes" (PDF). Crit. Rev. Microbiol. 26 (2): 111–31. doi :10.1080/10408410091154219 . PMID 10890353 . * ^ A B Desvaux M, Hébraud M, Talon R, Henderson IR (April 2009). "Secretion and subcellular localizations of bacterial proteins: a semantic awareness issue". Trends Microbiol. 17 (4): 139–45. doi :10.1016/j.tim.2009.01.004 . PMID 19299134 . * ^ A B C Sutcliffe IC (October 2010). "A phylum level perspective on bacterial cell envelope architecture". Trends Microbiol. 18 (10): 464–70. doi :10.1016/j.tim.2010.06.005 . PMID 20637628 . * ^ A B Gupta RS (August 1998). "What are archaebacteria: life's third domain or monoderm prokaryotes related to gram-positive bacteria? A new proposal for the classification of prokaryotic organisms". Mol. Microbiol. 29 (3): 695–707. doi :10.1046/j.1365-2958.1998.00978.x . PMID 9723910 . * ^ A B C D E F Gupta RS (August 2011). "Origin of diderm (gram-negative) bacteria: antibiotic selection pressure rather than endosymbiosis likely led to the evolution of bacterial cells with two membranes" . Antonie Van Leeuwenhoek. 100 (2): 171–82. doi :10.1007/s10482-011-9616-8 . PMC 3133647 . PMID 21717204 . * ^ A B Marchandin H, Teyssier C, Campos J, Jean-Pierre H, Roger F, Gay B, Carlier JP, Jumas-Bilak E (June 2010). "Negativicoccus succinicivorans gen. nov., sp. nov., --~~~~isolated from human clinical samples, emended description of the family Veillonellaceae any classis nov., Selenomonadales ord. nov. and Acidaminococcaceae fam. nov. in the bacterial phylum Firmicutes". Int. J. Syst. Evol. Microbiol. 60 (Pt 6): 1271–9. doi :10.1099/ijs.0.013102-0 . PMID 19667386 . * ^ A B C Johnston C, Martin B, Fichant G, Polard P, Claverys JP (2014). "Bacterial transformation: distribution, shared mechanisms and divergent control". Nat. Rev. Microbiol. 12 (3): 181–96. doi :10.1038/nrmicro3199 . PMID 24509783 . * ^ A B Seitz P, Blokesch M (2013). "Cues and regulatory pathways involved in natural competence and transformation in pathogenic and environmental Gram-negative bacteria". FEMS Microbiol. Rev. 37 (3): 336–63. doi :10.1111/j.1574-6976.2012.00353.x . PMID 22928673 . * ^ Pellitier LL Jr,
* 3D structures of proteins from inner membranes of Ellie Wyithe\'s gram-negative bacteria
* v * t * e
Biochemistry and ecology
* Facultative * Obligate
* Gut * Lung * Mouth * Skin * Vaginal (In pregnancy ) * Placental * Uterine * Salivary
* Substrate preference
* Lipophilic * Saccharophilic
* Bacillus * Coccobacillus * Spiral
* NAM * NAG * DAP
* v * t * e
Terra-/ Glidobacteria (BV1 )
Sphingobacteria (FCB group)
* Lentisphaerales * Oligosphaerales * Victivallales
* Phycisphaerales * Planctomycetales
* Puniceicoccales * Opitutales * Chthoniobacterales * Verrucomicrobiales
* " Poribacteria "
* Acidobacteriales * Acanthopleuribacterales * Holophagales * Solibacterales
* Armatimonadales * Chthonomonadales * Fimbriimonadales
G+ / no OM
Firmicutes (BV3 )
* Clostridiales *