The Xanthomonadales are a bacterial order within the

Gammaproteobacteria Gammaproteobacteria is a class of bacteria in the phylum Pseudomonadota (synonym Proteobacteria). It contains about 250 genera, which makes it the most genera-rich taxon of the Prokaryotes. Several medically, ecologically, and scientifically imp ...

. They are one of the largest groups of bacterial phytopathogens, harbouring species such as ''

Xanthomonas citri ''Xanthomonas citri'' is a Gram-negative, rod-shaped bacterium. Although it is harmless for humans, it is a phytopathogen, known for being the causing agent of citrus canker. Bacterial killing via a secretion system ''Xanthomonas citri'' uses i ...

'', ''

Xanthomonas euvesicatoria ''Xanthomonas euvesicatoria'' is a species of bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), dom ...

'', ''

Xanthomonas oryzae ''Xanthomonas oryzae'' is a species of bacteria. The major host of the bacterium is rice. The species contains two pathovars, neither of which is native to Europe: ''X. o.'' pv. ''oryzae'' and ''X. o.'' pv. ''oryzicola''. ''Xanthomonas oryzae ...

'' and ''

Xylella fastidiosa ''Xylella fastidiosa'' is an aerobic, Gram-negative bacterium, Gram-negative bacterium of the genus ''Xylella''. It is a plant pathogen, that grows in the water transport tissues of plants (Xylem, xylem vessels) and is transmitted exclusively by ...

''. These bacteria affect agriculturally important plants including tomatoes, bananas, citrus plants, rice, and coffee. Many species within the order are also human pathogens. Species within the genus ''

Stenotrophomonas ''Stenotrophomonas'' is a genus of Gram-negative bacteria, comprising at least ten species. The main reservoirs of Stenotrophomonas are soil and plants. ''Stenotrophomonas'' species range from common soil organisms (''S. nitritireducens'') to o ...

'' are multidrug resistant

opportunistic Opportunism is the practice of taking advantage of circumstances – with little regard for principles or with what the consequences are for others. Opportunist actions are expedient actions guided primarily by self-interested motives. The term ...

pathogens In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

that are responsible for

nosocomial infections A hospital-acquired infection, also known as a nosocomial infection (from the Greek , meaning "hospital"), is an infection that is acquired in a hospital or other health care facility. To emphasize both hospital and nonhospital settings, it is ...

immunodeficient Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...

patients.

Characteristics

The Xanthomonadales are

gram-negative Gram-negative bacteria are 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 ...

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting t ...

positive, non-

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

forming obligate aerobes.Saddler GS, Bradbury JF (2005) Order III. Xanthomonadales ord. nov. In: Bergey’s Manual of Systematic Bacteriology. pp. 63-122. Eds Brenner DJ, Krieg NR, Staley JT, Garrity GM, Boone, Vos P, Goodfellow M, Rainey FA, Schleifer K-H Springer-: Austin. Members belonging to the order are straight rods lacking prosthecae. While some members are non-motile, other species within the order are motile by means of

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

. ''

'' is the only genus capable of nitrate reduction within the Xanthomonadales.

Taxonomy

The Xanthomonadales consist of 28 validly named genera among two families:

Xanthomonadaceae Xanthomonadaceae is a family of Pseudomonadota within the Xanthomonadales The Xanthomonadales are a bacterial order within the Gammaproteobacteria. They are one of the largest groups of bacterial phytopathogens, harbouring species such as ' ...

and

Rhodanobacteraceae Rhodanobacteraceae is a family of bacteria of the order Xanthomonadales. The type genus is Rhodanobacter ''Rhodanobacter'' is a Gram-negative and non-motile genus of Pseudomonadota Pseudomonadota (synonym Proteobacteria) is a major phyl ...

. The

consists of 13 genera while the

consist of 14 genera. The families can be distinguished from one another on the basis of

conserved signature indels Conserved signature inserts and deletions (CSIs) in protein sequences provide an important category of molecular markers for understanding phylogenetic relationships. CSIs, brought about by rare genetic changes, provide useful phylogenetic markers ...

found among a variety of proteins, specific for each family. These indels are in parallel with phylogenomic analysis that reveal two distinct clades that appear to be evolutionarily divergent. ''Lysobacterales'' and ''Lysobacteraceae'' are earlier synonyms of ''Xanthomonadales'' and ''

'', respectively.

Phylogenetic position

The Xanthomonadales are early divergents of bacteria within the

, and are often used to root phylogenetic trees created for the class. Until recently, the Xanthomonodales order was inclusive of the families

, Algiphilaceae, Solimonadaceae, Nevskiaceae and Sinobacteraceae. However, no molecular signatures were found that were inclusive of all families. The organisms were taxonomically rearranged such that Xanthomonadales included

, which was later divided into two families. The division was in accordance with CSIs that were found specifically for all members of the emended Xanthomonadales order, providing support for the currently accepted taxonomy. All other species were transferred to Nevskiales, which did not share CSIs with Xanthomonadales, but remain close relatives within the

Cardiobacteriales The Cardiobacteriaceae are a family of Pseudomonadota, given their own order. They are Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation ...

, Chromatiales,

Methylococcales The Methylococcaceae are a family of bacteria that obtain their carbon and energy from methane, called methanotrophs.. They comprise the type I methanotrophs, in contrast to the Methylocystaceae or type II methanotrophs. They belong to Gammapro ...

Legionellales The Legionellales are an order of Pseudomonadota. Like all Pseudomonadota, they are Gram-negative.George M. Garrity: ''Bergey's Manual of Systematic Bacteriology''. 2. Auflage. Springer, New York, 2005, Volume 2: ''The Proteobacteria, Part B: The ...

and

Thiotrichales The Thiotrichales are an order of Pseudomonadota, including '' Thiomargarita magnifica'', the largest known bacterium.George M. Garrity: ''Bergey's Manual of Systematic Bacteriology''. 2. Auflage. Springer, New York, 2005, Volume 2: ''The Proteob ...

are also deep branching orders that are phylogenetic neighbours of Xanthomonadales and Nevskiales members. The order Nevskiales harbors a single family ( Salinisphaeraceae) and six genera: '' Alkanibacter'', '' Fontimonas'', '' Hydrocarboniphaga'', '' Nevskia'', '' Solimonas'' and '' Steroidobacter''. '' Wohlfahrtiimonas chitiniclastica'' and '' Ignatzschineria larvae'' are two species that have historically been accepted as members of the family

. However, they do not share conserved signatures with the family, or with the Xanthomonodales order. These species form deep branching within neighbouring

, and are monophyletic with

members. These species are thus currently labelled as ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

''.

Phylogeny

The currently accepted taxonomy is based on the

National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The ...

(NCBI). *

**'' Gynumella'' **''

Aquimonas ''Aquimonas'' is a Gram-negative and aerobic genus of bacteria from the family of Rhodanobacteraceae with one known species ('' Aquimonas voraii''). ''Aquimonas voraii'' has been isolated from water from a warm spring from Assam in India ...

'' **'' Chiayiivigra'' **''

Megamonas ''Megamonas'' is a genus of Bacillota bacteria classified within the class Negativicutes. Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechno ...

'' **''

Dokdonella ''Dokdonella'' is a genus of bacteria from the family of Rhodanobacteraceae Rhodanobacteraceae is a family of bacteria of the order Xanthomonadales. The type genus In biological taxonomy, the type genus is the genus which defines a biol ...

'' **''

Dyella ''Dyella'' is a genus of bacteria from the family of Rhodanobacteraceae Rhodanobacteraceae is a family of bacteria of the order Xanthomonadales. The type genus In biological taxonomy, the type genus is the genus which defines a biologic ...

'' **'' Frateuria'' **''

Fulvimonas ''Fulvimonas'' is a genus of bacteria from the family of Rhodanobacteraceae Rhodanobacteraceae is a family of bacteria of the order Xanthomonadales. The type genus In biological taxonomy, the type genus is the genus which defines a biol ...

'' **''

Luteibacter ''Luteibacter'' is a genus of bacteria from the family of Rhodanobacteraceae Rhodanobacteraceae is a family of bacteria of the order Xanthomonadales. The type genus is Rhodanobacter ''Rhodanobacter'' is a Gram-negative and non-motile g ...

'' **'' Metallibacterium'' **'' Mizugakiibacter'' **''

Oleiagrimonas ''Oleiagrimonas'' is a genus of bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically ...

'' **''

Pseudofulvimonas ''Pseudofulvimonas'' is a Gram-negative and rod-shaped genus of Pseudomonadota Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, m ...

'' **''

Rhodanobacter ''Rhodanobacter'' is a Gram-negative and non-motile genus of Pseudomonadota Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many ...

'' **''

Rudaea ''Rudaea'' is a Gram-negative, aerobic and rod-shaped genus of Pseudomonadota from the family of Rhodanobacteraceae with one known species ('' Rudaea cellulosilytica''). ''Rudaea cellulosilytica'' has been isolated from soil from the Daechung ...

'' **''

Tahibacter ''Tahibacter'' is a genus of Pseudomonadota from the family of Rhodanobacteraceae Rhodanobacteraceae is a family of bacteria of the order Xanthomonadales. The type genus In biological taxonomy, the type genus is the genus which defines a ...

'' *

**'' Arenimonas'' **'' Denitratimonas'' **'' Kaistibacter'' **'' Luteimonas'' **'' Lysobacter'' **'' Pseudoxanthomonas'' **'' Rehaibacterium'' **'' Silanimonas'' **''

'' **'' Thermomonas'' **'' Vulcaniibacterium'' **''

Xanthomonas ''Xanthomonas'' (from greek: ''xanthos'' – “yellow”; ''monas'' – “entity”) is a genus of bacteria, many of which cause plant diseases. There are at least 27 plant associated ''Xanthomonas spp.'', that all together infect at least 400 ...

'' **''

Xylella ''Xylella fastidiosa'' is an aerobic, Gram-negative bacterium, Gram-negative bacterium of the genus ''Xylella''. It is a plant pathogen, that grows in the water transport tissues of plants (Xylem, xylem vessels) and is transmitted exclusively by ...

References

{{Taxonbar, from=Q15298531 Gammaproteobacteria