Gammaproteobacteria

The element "gamma" (third letter of the Greek alphabet) indicates that this is Class III in Bergey's Manual of Systematic Bacteriology (Vol. II, page 1). Proteus refers to the Greek sea god who could change his shape. Bacteria (Greek βακτήριον; "rod" "little stick"), in terms of etymological history, refers to Bacillus (rod-shaped bacteria), but in this case is "useful in the interim while the phylogenetic data are being integrated into formal bacterial taxonomy."{{cite journal|last1=Stackebrandt|first1=E.|last2=Murray|first2=R. G. E.|last3=Truper|first3=H. G.|title=Proteobacteria classis nov., a Name for the Phylogenetic Taxon That Includes the "Purple Bacteria and Their Relatives"|journal=International Journal of Systematic Bacteriology|volume=38|issue=3|year=1988|pages=321–325|issn=0020-7713|doi=10.1099/00207713-38-3-321|doi-access=free}}

Currently, many different classifications are based on different approaches, such as

• the National Center for Biotechnology Information, based on a combination of Prokaryotic Code and sequence approaches
• List of Prokaryotic names with Standing in Nomenclature, based on the Prokaryotic Code
• ARB-Silva Database{{Cite web|title=Silva|url=https://www.arb-silva.de/|access-date=2020-11-22|website=www.arb-silva.de}} based on ribosomal RNA, or
• a multiprotein approach, such as Williams et al. 2010{{cite journal | vauthors = Williams KP, Gillespie JJ, Sobral BW, Nordberg EK, Snyder EE, Shallom JM, Dickerman AW | title = Phylogeny of gammaproteobacteria | journal = Journal of Bacteriology | volume = 192 | issue = 9 | pages = 2305–14 | date = May 2010 | pmid = 20207755 | pmc = 2863478 | doi = 10.1128/JB.01480-09 }} and Genome Taxonomy Database

It is (as of 2010) still very difficult to resolve the phylogeny of this bacterial class.

The following molecular phylogeny of Gammaproteobacteria is based on a set of 356 protein families.

{{cladogram

|style=width:800 px;

|title=Phylogeny of Gammaproteobacteria

|align=none

|caption=Phylogeny of Gammaproteobacteria after{{cite journal | vauthors = Williams KP, Gillespie JJ, Sobral BW, Nordberg EK, Snyder EE, Shallom JM, Dickerman AW | title = Phylogeny of gammaproteobacteria | journal = Journal of Bacteriology | volume = 192 | issue = 9 | pages = 2305–14 | date = May 2010 | pmid = 20207755 | pmc = 2863478 | doi = 10.1128/JB.01480-09 }} Not all orders are monophyletic, consequently families or genera are shown for the Pseudomonadales, Oceanospirillales, and Alteromonadales. In the case of singleton orders, the genus is shown. (In bacterial taxonomy, orders have the suffix -ales, while families have -aceae.)

|cladogram=

{{clade|1=Betaproteobacteria|label2=Gammaproteobacteria

|2={{clade|1=Xanthomonadales|2=

{{clade|1=Chromatiales

|2=Methylococcus

|3=Beggiatoa

|4={{clade

|1=Legionellales

|2=Ruthia, Vesicomyosocius, Thiomicrospira, Dichelobacter, Francisella

|3={{clade

|1={{clade|1=Moraxellaceae, Alcanivorax|2={{clade|1=Saccharophagus |2={{clade|1=Oceanospirillaceae|2={{clade|1=Marinobacter|2=Pseudomonadaceae}}}}}}

}}

|2={{clade|1=Pseudoalteromonadaceae, Alteromonas, Idiomarinaceae|2=

{{clade|1=Shewanellaceae|2={{clade|1=Psychromonadaceae|2={{clade|1=Aeromonadales|2={{clade|1=Vibrionales|2=

{{clade|1=Pasteurellales|2=Enterobacterales}}

}}}}}}}}

}}

}}

}}

}}

}}

}}

}}

A number of genera in Gammaproteobacteria have not yet been assigned to an order or family. These include Alkalimonas, Gallaecimonas, Ignatzschineria, Litorivivens, Marinicella, Plasticicumulans, Pseudohongiella, Sedimenticola, Thiohalobacter, Thiohalorhabdus, Thiolapillus, and Wohlfahrtiimonas.{{cite web|title=Classification of domains and phyla - Hierarchical classification of prokaryotes (bacteria) - Gammaproteobacteria|url=http://www.bacterio.net/-classifphyla.html#alkalimonas|access-date=13 January 2017|publisher=List of Prokaryotic Names with Standing in Nomenclature}}

Gammaproteobacteria, especially the orders Alteromonadales and Vibrionales, are fundamental in marine and coastal ecosystems because they are the major groups involved in nutrient cycling.{{cite journal | vauthors = Evans FF, Egan S, Kjelleberg S | title = Ecology of type II secretion in marine gammaproteobacteria | journal = Environmental Microbiology | volume = 10 | issue = 5 | pages = 1101–7 | date = May 2008 | pmid = 18218035 | doi = 10.1111/j.1462-2920.2007.01545.x | doi-access = free | bibcode = 2008EnvMi..10.1101E }} Despite their fame as pathogens, they find application in a huge number of fields, such as bioremediation and biosynthesis.

Gammaproteobacteria can be used as a microbial fuel cell (MFC){{cite journal | vauthors = Qian F, Morse DE | title = Miniaturizing microbial fuel cells | journal = Trends in Biotechnology | volume = 29 | issue = 2 | pages = 62–9 | date = February 2011 | pmid = 21075467 | doi = 10.1016/j.tibtech.2010.10.003 }} element that applies their ability to dissimilate various metals.{{cite journal | vauthors = Gorby YA, Yanina S, McLean JS, Rosso KM, Moyles D, Dohnalkova A, Beveridge TJ, Chang IS, Kim BH, Kim KS, Culley DE, Reed SB, Romine MF, Saffarini DA, Hill EA, Shi L, Elias DA, Kennedy DW, Pinchuk G, Watanabe K, Ishii S, Logan B, Nealson KH, Fredrickson JK | display-authors = 6 | title = Electrically conductive bacterial nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 30 | pages = 11358–63 | date = July 2006 | pmid = 16849424 | pmc = 1544091 | doi = 10.1073/pnas.0604517103 | bibcode = 2006PNAS..10311358G | doi-access = free }} The produced energy could be collected as one of the most environmentally friendly and sustainable energy production systems.{{cite journal | vauthors = Hau HH, Gralnick JA | title = Ecology and biotechnology of the genus Shewanella | journal = Annual Review of Microbiology | volume = 61 | issue = 1 | pages = 237–58 | date = September 2007 | pmid = 18035608 | doi = 10.1146/annurev.micro.61.080706.093257 }} They are also used as biological methane filters.{{Cite book |url=https://www.springer.com/gp/book/9783642389214|title=The Prokaryotes: Gammaproteobacteria|date=2014|publisher=Springer-Verlag|isbn=978-3-642-38921-4|edition=4th |location=Berlin Heidelberg|pages=434 | veditors = Rosenberg E, DeLong EF, Lory EF, Stackebrandt E, Erko T, Thompson F }}

Phototrophic purple sulfur bacteria are used in wastewater treatment processes.{{Cite journal| vauthors = Kobayashi M, Michiharu T, Tchan YT |date=1973-08-01|title=Treatment of industrial waste solutions and production of useful by-products using a photosynthetic bacterial method|url=https://dx.doi.org/10.1016%2F0043-1354%2873%2990075-4|journal=Water Research|language=en|volume=7|issue=8|pages=1219–1224|doi=10.1016/0043-1354(73)90075-4|bibcode=1973WatRe...7.1219K |issn=0043-1354|url-access=subscription}} The ability of some Gammaproteobacteria (e.g. the genus Alcanivorax{{cite journal | vauthors = Harayama S, Kishira H, Kasai Y, Shutsubo K | title = Petroleum biodegradation in marine environments | journal = Journal of Molecular Microbiology and Biotechnology | volume = 1 | issue = 1 | pages = 63–70 | date = August 1999 | pmid = 10941786 | url = https://pubmed.ncbi.nlm.nih.gov/10941786/#:~:text=Upon%20discharge%20into%20the%20sea,physical,%20chemical%20and%20biological%20modification.&text=In%20other%20words,%20the%20addition,the%20biodegradation%20of%20spilled%20oil }}) to bioremediate oil is increasingly important for degrading crude oil after oil spills.{{cite journal | vauthors = Kasai Y, Kishira H, Syutsubo K, Harayama S | title = Molecular detection of marine bacterial populations on beaches contaminated by the Nakhodka tanker oil-spill accident | journal = Environmental Microbiology | volume = 3 | issue = 4 | pages = 246–55 | date = April 2001 | pmid = 11359510 | doi = 10.1046/j.1462-2920.2001.00185.x | bibcode = 2001EnvMi...3..246K | url = https://pubmed.ncbi.nlm.nih.gov/11359510/ }} Some species from the family Chromatiaceae are notable because they may be involved in the production of vitamin B12.{{cite journal | vauthors = Koppenhagen VB, Schlingmann G, Schaer W, Dresow | title = Extracellular metabolites from phototrophic bacteria as possible intermediates in the biosynthesis of vitamin B12 |journal=Fermentation Products|pages=247–252| veditors = Moo-young M, Vezina C, Singh K |publisher=Pergamon |isbn=978-0-08-025385-5 }} Some Gammaproteobacteria are used to synthesize poly-b-hydroxyalkanoate (PHA),{{cite journal | vauthors = de la Haba RR, Sánchez-Porro C, Márquez MC, Ventosa A | title = Taxonomic study of the genus Salinicola: transfer of Halomonas salaria and Chromohalobacter salarius to the genus Salinicola as Salinicola salarius comb. nov. and Salinicola halophilus nom. nov., respectively | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 60 | issue = Pt 4 | pages = 963–971 | date = April 2010 | pmid = 19661506 | doi = 10.1099/ijs.0.014480-0 }} which is a polymer that is used in the production of biodegradable plastics. Many Gammaproteobacteria species are able to generate secondary metabolites with antibacterial properties.{{Cite web|title=Marine bacteria associated with marine macroorganisms: The potential antimicrobial resources - AMiner|url=https://www.aminer.org/pub/5488f7f645ce471f9099557f|access-date=2020-11-20|website=www.aminer.org}}

Gammaproteobacteria are widely distributed and abundant in various ecosystems such as soil, freshwater lakes and rivers, oceans and salt lakes. For example, they constitute about 6–20% (average of 14%) of bacterioplankton in different oceans,Broszat M, Nacke H, Blasi R, Siebe C, Huebner J, Daniel R, Grohmann E. (2014). Wastewater irrigation increases the abundance of potentially harmful Gammaproteobacteria in soils in Mezquital Valley, Mexico. Appl Environ Microbiol. and they are distributed worldwide in both deep-sea and coastal sediments.{{cite journal | vauthors = Bienhold C, Zinger L, Boetius A, Ramette A | title = Diversity and Biogeography of Bathyal and Abyssal Seafloor Bacteria | journal = PLOS ONE | volume = 11 | issue = 1 | pages = e0148016 | date = 2016-01-27 | pmid = 26814838 | pmc = 4731391 | doi = 10.1371/journal.pone.0148016 | bibcode = 2016PLoSO..1148016B | doi-access = free }} In seawater, bacterial community composition could be shaped by environmental parameters such as phosphorus availability, total organic carbon, salinity, and pH.{{cite journal| vauthors = Jiang H, Dong H, Ji S, Ye Y, Wu N |date=2007-09-26|title=Microbial Diversity in the Deep Marine Sediments from the Qiongdongnan Basin in South China Sea |journal=Geomicrobiology Journal |volume=24 |issue=6 |pages=505–517 |doi=10.1080/01490450701572473 |bibcode=2007GmbJ...24..505J |s2cid=130552094}} In soil, higher pH is correlated with higher relative abundance of Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria.{{cite journal | vauthors = Rousk J, Bååth E, Brookes PC, Lauber CL, Lozupone C, Caporaso JG, Knight R, Fierer N | title = Soil bacterial and fungal communities across a pH gradient in an arable soil | journal = The ISME Journal | volume = 4 | issue = 10 | pages = 1340–51 | date = October 2010 | pmid = 20445636 | doi = 10.1038/ismej.2010.58 | s2cid = 205156612 | doi-access = free | bibcode = 2010ISMEJ...4.1340R }} The relative abundance of Betaproteobacteria and Gammaproteobacteria is also positively correlated to the dissolved organic carbon (DOC) concentration, which is a key environmental parameter shaping bacterial community composition.{{cite journal | vauthors = Li D, Sharp JO, Saikaly PE, Ali S, Alidina M, Alarawi MS, Keller S, Hoppe-Jones C, Drewes JE | title = Dissolved organic carbon influences microbial community composition and diversity in managed aquifer recharge systems | journal = Applied and Environmental Microbiology | volume = 78 | issue = 19 | pages = 6819–28 | date = October 2012 | pmid = 22798375 | pmc = 3457517 | doi = 10.1128/AEM.01223-12 | bibcode = 2012ApEnM..78.6819L }} Gammaproteobacteria are also key players in the dark carbon fixation in coastal sediments, which are the largest carbon sink on Earth, and the majority of these bacteria have not been cultured yet.{{cite journal | vauthors = Hedges JI, Keil RG | title = Sedimentary organic matter preservation: an assessment and speculative synthesis. | journal = Marine Chemistry | date = April 1995 | volume = 49 | issue = 2–3 | pages = 81–115 | doi = 10.1016/0304-4203(95)00008-F | bibcode = 1995MarCh..49...81H }} The deep-sea hydrothermal system is one of the most extreme environments on Earth. Almost all vent-endemic animals are strongly associated with the primary production of the endo- and/or episymbiotic chemoautotrophic microorganisms.{{cite journal | vauthors = Jeanthon C | title = Molecular ecology of hydrothermal vent microbial communities | journal = Antonie van Leeuwenhoek | volume = 77 | issue = 2 | pages = 117–33 | date = February 2000 | pmid = 10768471 | doi = 10.1023/a:1002463825025 | s2cid = 24324674 }} Analyses of both the symbiotic and free-living microbial communities in the various deep-sea hydrothermal environments have revealed a predominance in biomass of members of the Gammaproteobacteria.{{cite journal | vauthors = Stewart FJ, Newton IL, Cavanaugh CM | title = Chemosynthetic endosymbioses: adaptations to oxic-anoxic interfaces | journal = Trends in Microbiology | volume = 13 | issue = 9 | pages = 439–48 | date = September 2005 | pmid = 16054816 | doi = 10.1016/j.tim.2005.07.007 }}

Gammaproteobacteria have a wide diversity, metabolic versatility, and functional redundancy in the hydrothermal sediments, and they are responsible for the important organic carbon turnover and nitrogen and sulfur cycling processes.{{cite journal | vauthors = Baker BJ, Lazar CS, Teske AP, Dick GJ | title = Genomic resolution of linkages in carbon, nitrogen, and sulfur cycling among widespread estuary sediment bacteria | journal = Microbiome | volume = 3 | pages = 14 | date = 2015 | pmid = 25922666 | pmc = 4411801 | doi = 10.1186/s40168-015-0077-6 | doi-access = free }} Anoxic hydrothermal fluids contain several reduced compounds such as H₂, CH₄, and reduced metal ions in addition to H₂S. Chemoautotrophs that oxidize hydrogen sulfide and reduce oxygen potentially sustain the primary production in these unique ecosystems.Jannasch, H.W., andMottl, M.J. (1985). Geomicrobiology of deep-sea hydrothermal vents. Science 229, 717–725 In the last decades, it has been found that orders belonging to Gammaproteobacteria, like Pseudomonas, Moraxella, are able to degrade different types of plastics, and these microbes might have a key role in plastic biodegradation.{{cite web|last=Soixanteseize|date=2015-01-06|title=Explore to understand, share to bring about change|url=https://oceans.taraexpeditions.org/en/m/science/news/bacterial-degradation-of-synthetic-plastics/|access-date=2020-11-22|website=Fondation Tara Océan|language=en-US}}

Gammaproteobacteria are metabolically diverse, employing a variety of electron donors for respiration and biosynthesis.

Some groups are nitrite-oxidizers{{cite journal | vauthors = Han S, Li X, Luo X, Wen S, Chen W, Huang Q | title = Nitrite-Oxidizing Bacteria Community Composition and Diversity Are Influenced by Fertilizer Regimes, but Are Independent of the Soil Aggregate in Acidic Subtropical Red Soil | language = en | journal = Frontiers in Microbiology | volume = 9 | pages = 885 | date = 2018 | pmid = 29867799 | pmc = 5951965 | doi = 10.3389/fmicb.2018.00885 | doi-access = free }} and ammonia oxidizers like the members of Nitrosococcus (with the exception of Nitrosococcus mobilis) and they are also obligate halophilic bacteria.Cesar Mota, Jennifer Ridenoure, Jiayang Cheng, Francis L. de los Reyes, High levels of nitrifying bacteria in intermittently aerated reactors treating high ammonia wastewater. FEMS Microbiology Ecology, Volume 54, Issue 3, November 2005, pp. 391–400

Others are chemoautotrophic sulfur-oxidizers, like Thiotrichales, which are found in communities such as filamentous microbial biofilms in the Tor Caldara shallow-water gas vent in the Tyrrhenian Sea.{{cite journal | vauthors = Patwardhan S, Foustoukos DI, Giovannelli D, Yücel M, Vetriani C | title = Gammaproteobacteria During Colonization of a Shallow-Water Gas Vent | language = en | journal = Frontiers in Microbiology | volume = 9 | pages = 2970 | date = 2018 | pmid = 30574130 | pmc = 6291522 | doi = 10.3389/fmicb.2018.02970 | doi-access = free }} Moreover, thanks to 16S rRNA gene analysis, different sulfide oxidizers in the Gammaporteobacteria class have been detected, and the most important among them are Beggiatoa, Thioploca and Thiomargarita; besides, large amounts of hydrogen sulfide are produced by sulfate-reducing bacteria in organic-rich coastal sediments.Sabine Lenk, Julia Arnds, Katrice Zerjatke, Niculina Musat, Rudolf Amann and Marc Mußmann* Max Planck Institute for Marine Microbiology, Celsiusstraße 1, 28359 Bremen, Germany. Novel groups of Gammaproteobacteria catalyse sulfur oxidation and carbon fixation in a coastal, intertidal sediment. (2011)

Marine Gammaproteobacteria include aerobic anoxygenic phototrophic bacteria (AAP) that use bacteriochlorophyll to support the electron transport chain. They are believed to be a widespread and essential community in the oceans.{{cite journal | vauthors = Cho JC, Stapels MD, Morris RM, Vergin KL, Schwalbach MS, Givan SA, Barofsky DF, Giovannoni SJ | display-authors = 6 | title = Polyphyletic photosynthetic reaction centre genes in oligotrophic marine Gammaproteobacteria | journal = Environmental Microbiology | volume = 9 | issue = 6 | pages = 1456–63 | date = June 2007 | pmid = 17504483 | doi = 10.1111/j.1462-2920.2007.01264.x | bibcode = 2007EnvMi...9.1456C | url = https://sfamjournals.onlinelibrary.wiley.com/doi/abs/10.1111/j.1462-2920.2007.01264.x | url-access = subscription }}

Methanotrophs, such as the order Methylococcales, metabolize methane as sole energy source and are very important in the global carbon cycle. They are found in any site with methane sources, like gas reserves, soils, and wastewater.{{cite journal | vauthors = Orata FD, Meier-Kolthoff JP, Sauvageau D, Stein LY | title = Methylococcales) Calls for the Reclassification of Members at the Genus and Species Levels | language = en | journal = Frontiers in Microbiology | volume = 9 | pages = 3162 | date = 2018 | pmid = 30631317 | pmc = 6315193 | doi = 10.3389/fmicb.2018.03162 | doi-access = free }}

Purple sulfur bacteria are anoxygenic phototrophs that oxidize sulfur,{{Cite book | chapter= An Overview of Purple Bacteria: Systematics, Physiology, and Habitats | doi = 10.1007/978-1-4020-8815-5_1 | pages= 1–15 | publisher= Springer | first1= Michael T. | last1= Madigan | first2= Deborah O. | last2= Jung | date= 2009 | title=The Purple Phototropic Bacteria | isbn =978-1-4020-8814-8 | ol = OL25552439M | series= Advances in Photosynthesis and Respiration, vol. 28 | editor1= C. Neil Hunter| editor2= Fevzi Daldal |editor3= Marion C. Thurnauer |editor4= J. Thomas Beatty}} but potentially also other substrates like iron.{{cite journal | vauthors = Bryce C, Blackwell N, Schmidt C, Otte J, Huang YM, Kleindienst S, Tomaszewski E, Schad M, Warter V, Peng C, Byrne JM, Kappler A | display-authors = 6 | title = Microbial anaerobic Fe(II) oxidation - Ecology, mechanisms and environmental implications | journal = Environmental Microbiology | volume = 20 | issue = 10 | pages = 3462–3483 | date = October 2018 | pmid = 30058270 | doi = 10.1111/1462-2920.14328 | s2cid = 51865641 | doi-access = free | bibcode = 2018EnvMi..20.3462B }} They are represented by members of two families, Chromatiaceae (e.g. Allochromatium, Chromatium, Thiodicyton) and Ectothiorhodospiraceae (e.g. Ectothiorhodospira). A few species within the genus Thermomonas (order Lysobacter) carry out the same metabolism.Sabrina Hedrich, Michael Schlomann and D. Barrie Johnson. The iron-oxidizing proteobacteria. School of Biological Sciences, College of Natural Sciences, Bangor University, Deiniol Road, Bangor LL57 2UW, UK 2 Interdisciplinary Ecological Center, TU Bergakademie Freiberg, Leipziger Strasse 29, 09599 Freiberg, Germany. (2011)

Numerous genera are obligate or generalist hydrocarbonclasts. The obligate hydrocarbonoclastic bacteria (OHCB) use hydrocarbons almost exclusively as a carbon source; until now{{when|date=October 2024}} they have been found only in the marine environment. Examples include Alcanivorax, Oleiphilus, Oleispira, Thalassolitus, Cycloclasticus and Neptunomonas, and some species of Polycyclovorans, Algiphilus (order Xanthomonadales), and Porticoccus hydrocarbonoclasticus (order Cellvibrionales) that were isolated from phytoplankton. In contrast, aerobic “generalist” hydrocarbon degraders can use either hydrocarbons or nonhydrocarbon substrates as sources of carbon and energy; examples are found in the genera Acinetobacter, Colwellia, Glaciecola, Halomonas, Marinobacter, Marinomonas, Methylomonas, Pseudoalteromonas, Pseudomonas, Rhodanobacter, Shewanella, Stenotrophomonas, and Vibrio.Terry J. McGenity, Taxonomy, Genomics and Ecophysiology of Hydrocarbon-Degrading Microbes, 2019 143-152; 181-189; 191-205.

The most widespread pathway for carbon fixation among Gammaproteobacteria is the Calvin–Benson–Bassham (CBB) cycle, although a minority may use the rTCA cycle.{{cite journal | vauthors = Markert S, Arndt C, Felbeck H, Becher D, Sievert SM, Hügler M, Albrecht D, Robidart J, Bench S, Feldman RA, Hecker M, Schweder T | display-authors = 6 | title = Physiological proteomics of the uncultured endosymbiont of Riftia pachyptila | journal = Science | volume = 315 | issue = 5809 | pages = 247–50 | date = January 2007 | pmid = 17218528 | doi = 10.1126/science.1132913 | bibcode = 2007Sci...315..247M | hdl = 1912/1514 | s2cid = 45745396 | url = https://www.science.org/doi/10.1126/science.1132913 | hdl-access = free }} Thioflavicoccus mobilis (a free living species) and "Candidatus Endoriftia persephone" (symbiont of the giant tubeworm Riftia pachyptila) may use the rTCA cycle in addition to the CBB cycle, and may express these two different pathways simultaneously.{{cite journal | vauthors = Rubin-Blum M, Dubilier N, Kleiner M | title = Genetic Evidence for Two Carbon Fixation Pathways (the Calvin-Benson-Bassham Cycle and the Reverse Tricarboxylic Acid Cycle) in Symbiotic and Free-Living Bacteria | journal = mSphere | volume = 4 | issue = 1 | date = January 2019 | pmid = 30602523 | pmc = 6315080 | doi = 10.1128/mSphere.00394-18 }}

Symbiosis is a close and a long-term biological interaction between two different biological organisms. A large number of Gammaproteobacteria are able to join in a close endosymbiosis with various species. Evidence for this can be found in a wide variety of ecological niches: on the ground,{{cite journal | vauthors = Karamipour N, Fathipour Y, Mehrabadi M | title = Gammaproteobacteria as essential primary symbionts in the striped shield bug, Graphosoma Lineatum (Hemiptera: Pentatomidae) | journal = Scientific Reports | volume = 6 | issue = 1 | pages = 33168 | date = September 2016 | pmid = 27609055 | doi = 10.1038/srep33168 | pmc = 5016839 | bibcode = 2016NatSR...633168K | url = }}{{cite journal | vauthors = Kikuchi Y, Hosokawa T, Nikoh N, Fukatsu T | title = Gut symbiotic bacteria in the cabbage bugs Eurydema rugosa and Eurydema dominulus (Heteroptera: Pentatomidae). | journal = Applied Entomology and Zoology | date = February 2012 | volume = 47 | issue = 1 | pages = 1–8 | doi = 10.1007/s13355-011-0081-7 | bibcode = 2012AppEZ..47....1K | s2cid = 14943700 }} within plants,{{cite journal | vauthors = Tannenbaum I, Kaur J, Mann R, Sawbridge T, Rodoni B, Spangenberg G | title = Profiling the Lolium perenne microbiome: from seed to seed. | journal = Phytobiomes Journal | date = August 2020 | volume = 4 | issue = 3 | pages = 281–9 | doi = 10.1094/PBIOMES-03-20-0026-R | doi-access = free }} or deep on the ocean floor.{{cite journal | vauthors = Breusing C, Schultz DT, Sudek S, Worden AZ, Young CR | title = High-contiguity genome assembly of the chemosynthetic gammaproteobacterial endosymbiont of the cold seep tubeworm Lamellibrachia barhami.|journal=Molecular Ecology Resources | date = September 2020 | volume = 20 | issue = 5 | pages = 1432–44 | doi = 10.1111/1755-0998.13220 | pmc = 7540712 }} On the land, it has been reported that Gammaproteobacteria species have been isolated from Robinia pseudoacacia{{cite journal | vauthors = Shiraishi A, Matsushita N, Hougetsu T | title = Nodulation in black locust by the Gammaproteobacteria Pseudomonas sp. and the Betaproteobacteria Burkholderia sp | journal = Systematic and Applied Microbiology | volume = 33 | issue = 5 | pages = 269–74 | date = August 2010 | pmid = 20542651 | doi = 10.1016/j.syapm.2010.04.005 | bibcode = 2010SyApM..33..269S }} and other plants,{{Cite journal| vauthors = Ghosh PK, De TK, Maiti TK |date=2015-04-01|title=Ascorbic acid production in root, nodule and Enterobacter spp. (Gammaproteobacteria) isolated from root nodule of the legume Abrus precatorius L. |journal=Biocatalysis and Agricultural Biotechnology |volume=4|issue=2|pages=127–134|doi=10.1016/j.bcab.2014.11.006 }}{{cite journal | vauthors = Benhizia Y, Benhizia H, Benguedouar A, Muresu R, Giacomini A, Squartini A | title = Gamma proteobacteria can nodulate legumes of the genus Hedysarum | journal = Systematic and Applied Microbiology | volume = 27 | issue = 4 | pages = 462–8 | date = August 2004 | pmid = 15368852 | doi = 10.1078/0723202041438527 | bibcode = 2004SyApM..27..462B }} while in the deep sea a sulfur-oxidizing gammaproteobacteria was found in a hydrothermal vent chimney;{{cite journal | vauthors = Nunoura T, Takaki Y, Kazama H, Kakuta J, Shimamura S, Makita H, Hirai M, Miyazaki M, Takai K | display-authors = 6 | title = Physiological and genomic features of a novel sulfur-oxidizing gammaproteobacterium belonging to a previously uncultivated symbiotic lineage isolated from a hydrothermal vent | journal = PLOS ONE | volume = 9 | issue = 8 | pages = e104959 | date = 2014-08-18 | pmid = 25133584 | pmc = 4136832 | doi = 10.1371/journal.pone.0104959 | bibcode = 2014PLoSO...9j4959N | doi-access = free }} by entering into symbiotic relationships in deep sea areas, sulfur-oxidizing chemolithotrophic microbes receive additional organic hydrocarbons in hydrothermal ecosystems. Some Gammaproteobacteria are symbiotic with geothermic ocean vent-downwelling animals,{{cite web|author=Holt JR|date=6 February 2013|title=Description of the Phylum Gammaproteobacteria|url=http://comenius.susqu.edu/biol/202/eubacteria/proteobacteriae/gammaproteobacteria/default.htm|access-date=17 April 2018|website=Susquehanna University - Systematic Biology Course Website}} and in addition, Gammaproteobacteria can have complex relationships with other species that live around thermal springs,{{cite journal | vauthors = Petersen JM, Ramette A, Lott C, Cambon-Bonavita MA, Zbinden M, Dubilier N | title = Dual symbiosis of the vent shrimp Rimicaris exoculata with filamentous gamma- and epsilonproteobacteria at four Mid-Atlantic Ridge hydrothermal vent fields | journal = Environmental Microbiology | volume = 12 | issue = 8 | pages = 2204–18 | date = August 2010 | pmid = 21966914 | doi = 10.1111/j.1462-2920.2009.02129.x | doi-access = free | bibcode = 2010EnvMi..12.2204P | hdl = 21.11116/0000-0001-CADC-4 | hdl-access = free }} for example, with the shrimp Rimicaris exoculata living from hydrothermal vents on the Mid-Atlantic Ridge.

Regarding the endosymbionts, most of them lack many of their family characteristics due to significant genome reduction.{{cite journal | vauthors = Shigenobu S, Watanabe H, Hattori M, Sakaki Y, Ishikawa H | title = Genome sequence of the endocellular bacterial symbiont of aphids Buchnera sp. APS | journal = Nature | volume = 407 | issue = 6800 | pages = 81–6 | date = September 2000 | pmid = 10993077 | doi = 10.1038/35024074 | bibcode = 2000Natur.407...81S | s2cid = 4405072 | doi-access = free }}{{cite journal | vauthors = Burke GR, Moran NA | title = Massive genomic decay in Serratia symbiotica, a recently evolved symbiont of aphids | journal = Genome Biology and Evolution | volume = 3 | pages = 195–208 | date = 2011 | pmid = 21266540 | pmc = 3056288 | doi = 10.1093/gbe/evr002 }}

Gammaproteobacteria include several medically and scientifically important groups of bacteria, such as the families Enterobacteriaceae, Vibrionaceae, and Pseudomonadaceae. A number of human pathogens belong to this class, including Yersinia pestis, Vibrio cholerae, Pseudomonas aeruginosa, Escherichia coli, and some species of Salmonella. The class also contains plant pathogens such as Xanthomonas axonopodis pv. citri (citrus canker), Pseudomonas syringae pv. actinidiae (kiwifruit Psa outbreak), and Xylella fastidiosa. In the marine environment, several species from this class can infect different marine organisms, such as species in the genus Vibrio which affect fish, shrimp, corals or oysters,{{cite journal|vauthors=Evans FF, Egan S, Kjelleberg S|date=May 2008|title=Ecology of type II secretion in marine gammaproteobacteria|journal=Environmental Microbiology|volume=10|issue=5|pages=1101–7|doi=10.1111/j.1462-2920.2007.01545.x|pmid=18218035|doi-access=free|bibcode=2008EnvMi..10.1101E }} and species of Salmonella which affect grey seals (Halichoerus grypus).{{cite journal|display-authors=6|vauthors=Baily JL, Foster G, Brown D, Davison NJ, Coia JE, Watson E, Pizzi R, Willoughby K, Hall AJ, Dagleish MP|date=March 2016|title=Salmonella infection in grey seals (Halichoerus grypus), a marine mammal sentinel species: pathogenicity and molecular typing of Salmonella strains compared with human and livestock isolates|url=http://doi.wiley.com/10.1111/1462-2920.13219|journal=Environmental Microbiology|volume=18|issue=3|pages=1078–87|doi=10.1111/1462-2920.13219|pmid=26768299|bibcode=2016EnvMi..18.1078B |url-access=subscription}}{{cite journal | vauthors = Daniels NA, MacKinnon L, Bishop R, Altekruse S, Ray B, Hammond RM, Thompson S, Wilson S, Bean NH, Griffin PM, Slutsker L | title = Vibrio parahaemolyticus infections in the United States, 1973-1998 | journal = The Journal of Infectious Diseases | volume = 181 | issue = 5 | pages = 1661–6 | date = May 2000 | pmid = 10823766 | doi = 10.1086/315459 | doi-access = free }}

• Betaproteobacteria
• Pseudomonadota

{{Reflist|30em}}

• {{MeshName|Gammaproteobacteria}}

{{Bacteria classification}}

{{Gram-negative proteobacterial bacterial diseases}}

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Category:Pseudomonadota