Characteristics of the genus Xknthomonas. Following a suggestion by Burkholder (2), Dowson (4) created the name Xanthomonas for a well-defined subgroup of yellow-pigmented phytopathogenic pseudomonads which had been placed together with many other unrelated bacteria in the genus Phytomonas. Dowson (4) defined Xanthomonas as follows: "non-sporing, rod-shaped bacteria. Gram-negative, motile by one polar flagellum (rarely 2 present), or nonmotile, yellow in the mass on nutrient agar and on sterile potato, on both of which abundant slimy growths are formed. Most species digest starch and produce acid in lactose; none produces acid in salicin. " Two corrections were made later by Dowson: deletion of nonmotility and a change from nutrient agar to nutrient glucose agar (5).In subsequent definitions of the genus, the following characteristics were added: absence of poly-P-hydroxybutyrate inclusions, production of highly characteristic brominated aryl-polyene yellow pigments (xanthomonadins), infrequent production of a diffusible, brown color in beef extract agar, digestion of proteins, production of hydrogen sulfide, inability to use asparagine as the sole source of carbon and nitrogen, absence of denitrification and of nitrate reduction, negative or weak oxidase reaction, inhibition of growth by 0.1% (and frequently by 0.02%) triphenyltetrazolium chloride, requirement for growth factors (usually methionine, glutamic acid, nicotinic acid, or a combination of these), optimal growth temperature of 25 to 27"C, DNA base composition (63 to 71 mol% G+C), and plant pathogenicity. Thus far, presence of pili has not been reported for any of the species (1). The slimes produced by various * Corresponding author. species and pathovars were identified as anionic exopolysaccharides, to which the common name "xanthan gums" has been applied. These compounds have very interesting properties and may play a role in the interactions of the pathogens with their respective plant hosts (17). As pointed out by Dye (6), these organisms "form a well-defined remarkably uniform group from which other yellow-pigmented, Gramnegative, monotrichous, aerobic, non-sporing organisms can be distinguished in the laboratory without difficulty."In Bergey's Manual of Systematic Bacteriology (l), five well-characterized species (X. campestris, X. fragariae, X. albilineans, X. axonopodis, and X. ampelina) are described; one of these, X. campestris, is subdivided into many pathovars that are named according to the host plant of origin. The five species accepted by Bradbury (I) were those already included in the 8th edition of Beeey ' s Manual of Determinative Bacteriology (8), but a sixth species of doubtful affiliation (X. populi) was added. For the list of pathovars, Bradbury accepted the one given by Dye et al. (7) and added only two.A review of the genus Xanthomonas was included in the first edition of the treatise The Prokalyotes: a Handbook on Habitats, Isolation and Identification of Bacteria (26). Unfortunately, aside from a summary of the general prope...

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Xan.tho' mo.nas or Xan.tho.mo' nas . * Gr. adj. xanthus yellow; Gr. fem. n. monas unit, monad; M.L. fem. n. Xanthomonas yellow monad. Proteobacteria / Gammaproteobacteria / Xanthomonadales / Xanthomonadaceae / Xanthomonas Straight rods, 0.4–0.6 × 0.8–2.0 μm , mostly single or in pairs, occasionally short chains, filaments rarely seen. Gram negative. Do not produce poly‐β‐hydroxybutyrate inclusions, nor have sheaths, prosthecae, or resting stages. Motile by a single polar flagellum. Obligately aerobic, having a strictly respiratory type of metabolism with oxygen as the terminal electron acceptor. No denitrification or nitrate reduction occurs. Colonies are usually yellow , smooth and butyrous, mucoid or viscid. The pigments are highly characteristic brominated aryl polyenes or “xanthomonadins”. A characteristic extracellular acidic heteropolysaccharide called xanthan is produced by most strains giving the viscous consistency. Growth is inhibited by 6% NaCl, 30% glucose, 0.01% lead acetate, methyl green, or thionin, and by 0.1% (and usually by 0.02%) triphenyl tetrazolium chloride. Catalase positive; oxidase negative or weak ; urease not produced. H 2 S is usually produced, but not indole or acetoin. Acid is not produced in litmus milk or purple milk. Chemoorganotrophic; able to use various carbohydrates and salts of organic acids as sole carbon sources. Small amounts of acid are produced from many carbohydrates, but not from l‐rhamnose, adonitol, sorbose, d‐sorbitol, meso ‐inositol, or meso ‐erythritol. Metabolic activity is shown in Biolog GN microplate tests with d‐fructose, d‐glucose, d‐mannose and methylpyruvate, but not with α‐cyclodextrin, adonitol, D ‐arabitol, meso ‐erythritol, meso ‐inositol, xylitol, D ‐glucosaminate, γ‐hydroxybutyrate, itaconate, sebacate, L ‐ornithine, L ‐pyroglutamate, D ‐serine, D , L ‐carnitine, γ‐aminobutyrate, phenylethylamine, putrescine, 2‐aminoethanol, or 2,3‐butanediol. L ‐asparagine, L ‐glutamine, and glycine cannot be used as sole sources of both carbon and nitrogen. Among the nine fatty acids that predominate in whole cell preparations are 9‐methyl decanoic acid (C 11:0 iso ), 3‐hydroxy‐9‐methyl decanoic acid (C 11:0 iso 3OH ), and 3‐hydroxy‐11‐methyl dodecanoic acid (C 13:0 iso 3OH ), which are highly characteristic of this genus. The ubiquinone that is present has eight isoprene units. Spermidine is the main polyamine; spermine is usually detectable, but not 2‐hydroxyputrescine or 1,3‐diaminopropane. Species so far described are plant pathogens or are plant associated. The mol % G + C of the DNA is : 63.3–69.7 ( T m ). Type species : Xanthomonas campestris (Pammel 1895) Dowson 1939, 190, emend. Vauterin Hoste, Kersters and Swings 1995, 484 (“ Bacillus campestris ” Pammel 1895, 130.)

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