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 genus-rich taxon of the Prokaryotes. Several medically, ecologically, and scienti ...

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

Xanthomonas citri ''Xanthomonas citri'' is a Gram-negative bacteria, Gram-negative, Bacillus (shape), rod-shaped bacterium. Although it is harmless for humans, it is a phytopathology, phytopathogen, known for being the causing agent of citrus canker. Many pathova ...

'', '' Xanthomonas euvesicatoria'', ''

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 of the genus ''Xylella''. It is a plant pathogen, that grows in the water transport tissues of plants ( xylem vessels) and is transmitted exclusively by xylem sap-feeding insects suc ...

''. These bacteria affect agriculturally important plants including tomatoes, bananas, citrus plants, rice, and coffee. Species within the genus ''

Stenotrophomonas ''Stenotrophomonas'' is a genus of Gram-negative bacteria, comprising at least twenty-six species. The main reservoirs of ''Stenotrophomonas'' are soil and plants. ''Stenotrophomonas'' species range from common soil organisms (''S. nitritireduc ...

'' are multidrug resistant

opportunistic 300px, ''Opportunity Seized, Opportunity Missed'', engraving by Theodoor Galle, 1605 Opportunism is the practice of taking advantage of circumstances — with little regard for principles or with what the consequences are for others. Opport ...

pathogens In biology, a pathogen (, "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. The term ...

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 healthcare facility. To emphasize both hospital and nonhospital settings, it is s ...

immunodeficient Immunodeficiency, also known as immunocompromise, 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 affec ...

patients.

Characteristics

The Xanthomonadales are

gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

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 ...

positive, non-

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

forming obligate

aerobes An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. The ability to exhibit aerobic respiration may yield benefits to the aerobic organism, as aerobic respiration yields more energy than anaerobic ...

.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 Prosthecate bacteria are a non-phylogenetically related group of Gram-negative bacteria that possess appendages, termed prosthecae. These cellular appendages, also known as ''stalks'', are neither Pilus, pili nor flagella, as they are extensions o ...

. While some members are non-motile, other species within the order are motile by means of

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. ''

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

and

Rhodanobacteraceae Rhodanobacteraceae is a family of bacteria of the order Xanthomonadales. The type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological no ...

. 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, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining m ...

, 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 Gammapr ...

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

and

Thiotrichales Thiotrichales is an order of sulfur-oxidizing bacteria within the class Gammaproteobacteria known for their large size and ability to live in sulfur rich environments. Characteristics Thiotrichales has an important role in the sulfur and nitrog ...

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 ''Wohlfahrtiimonas chitiniclastica'' is a bacterium from the genus of '' Wohlfahrtiimonas'' which has been first isolated from the larva of ''Wohlfahrtia magnifica'' from Budapest in Hungary. ''Wohlfahrtiimonas chitiniclastica'' can cause sepsis ...

'' 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 is a term used for a taxonomy (biology), 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 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 is lo ...

(NCBI). *

**'' Gynumella'' **'' Aquimonas'' **'' Chiayiivigra'' **'' Megamonas'' **'' Dokdonella'' **'' Dyella'' **'' Frateuria'' **'' Fulvimonas'' **'' Luteibacter'' **'' Metallibacterium'' **'' Mizugakiibacter'' **'' Oleiagrimonas'' **'' Pseudofulvimonas'' **'' Rhodanobacter'' **'' Rudaea'' **'' Tahibacter'' *

**''

Arenimonas ''Arenimonas'' is a genus of Pseudomonadota from the family Xanthomonadaceae Xanthomonadaceae is a family of Pseudomonadota within the order Xanthomonadales The Xanthomonadales are a bacterial order within the Gammaproteobacteria. They are ...

'' **'' 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 pathology, plant diseases. There are at least 27 plant associated ''Xanthomonas spp.'', that all together infect at l ...

'' **'' Xylella''

References

{{Taxonbar, from=Q15298531 Gammaproteobacteria