[5] Diverse metabolisms are found in Gammaproteobacteria; there are both aerobic and anaerobic (obligate or facultative) species, chemolithoautotrophics, chemoorganotrophics, photoautotrophs and heterotrophs.
[6] The element "gamma" (third letter of the Greek alphabet) indicates that this is Class III in Bergey's Manual of Systematic Bacteriology (Vol.
Betaproteobacteria Xanthomonadales Chromatiales Methylococcus Beggiatoa Legionellales Ruthia, Vesicomyosocius, Thiomicrospira, Dichelobacter, Francisella Moraxellaceae, Alcanivorax Saccharophagus Oceanospirillaceae Marinobacter Pseudomonadaceae Pseudoalteromonadaceae, Alteromonas, Idiomarinaceae Shewanellaceae Psychromonadaceae Aeromonadales Vibrionales Pasteurellales 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.
[9] Gammaproteobacteria, especially the orders Alteromonadales and Vibrionales, are fundamental in marine and coastal ecosystems because they are the major groups involved in nutrient cycling.
[22] In seawater, bacterial community composition could be shaped by environmental parameters such as phosphorus availability, total organic carbon, salinity, and pH.
[24] 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.
[27] 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.
[28] 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.
[33] 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.
[35] Marine Gammaproteobacteria include aerobic anoxygenic phototrophic bacteria (AAP) that use bacteriochlorophyll to support the electron transport chain.
[36] Methanotrophs, such as the order Methylococcales, metabolize methane as sole energy source and are very important in the global carbon cycle.
[47] On the land, it has been reported that Gammaproteobacteria species have been isolated from Robinia pseudoacacia[48] and other plants,[49][50] while in the deep sea a sulfur-oxidizing gammaproteobacteria was found in a hydrothermal vent chimney;[51] by entering into symbiotic relationships in deep sea areas, sulfur-oxidizing chemolithotrophic microbes receive additional organic hydrocarbons in hydrothermal ecosystems.
A number of human pathogens belong to this class, including Yersinia pestis, Vibrio cholerae, Pseudomonas aeruginosa, Escherichia coli, and some species of Salmonella.