These are Gram-negative, non-sporing non-acid fast rods, which are generally straight but may be slightly curved. They are generally motile with polar flagellae. They lack sheaths or prosthecae. They are chemoorganotrophs with a respiratory metabolism. They do not ferment carbohydrates, do not fix nitrogen and are not photosynthetic. They can grow on a variety of organic substrates except one-carbon compounds. There are currently four genera accepted in the family. The genus Pseudomonas is the type genus. The other genera are Xanthomonas, Zoogloea and Fraturia. The GC content of the DNA is 55-70 mol%.

Genera

Pseudomonas: There are currently many species recognized within this genus with the species being grouped into five similarity groups based on their rRNA similaruty. They are usually motile. They are oxidase positive and capable of growing in simple media utilising a large variety of low-molecular-compounds. They do not require organic growth factors. The saprophytic Pseudomona species are frequently found in nature and often are a major or important component of the microflora and should be considered ubiquitous. They can grow in association with many microorganisms. They are frequently found in soil, growing well at neutral or around neutral pH in the mesophilic temperature range. Many soil pseudomonads are fluorescent. Phytopathogenic pseudomanads generally have narrow host ranges, where they appear as practically pure cultures. Apart from Ps. mallei the animal and human pathogenic pseudomonads are not very host specific. The reconized species include P. aeruginosa, P. cepacia , P. chlororaphis, P. cichori, P. fluorescens, P. mallei, P. pseudomallei, P. putida, P. solanacearum, P. stutzeri, P. syringae, and P. testosteroni. Many strains can cause human infection. They tend to have a sheathed polar flagellum. Na+ stimulates their growth or may even be required and they are sensitive to the vibriostatic compound 0129. They produce lipase and ferment D-mannitol. The GC content of the DNA is 55-64 mol%.

Xanthomonas: They form water-insoluble yellow pigments. Many are phytopathogens. They require organic growth factors. Their growth on nutrient agar is inhibited by 0.1% tetrazolium chloride. They have a weak oxidase reaction or are oxidase negative.The GC content of the DNA is 63-70 mol%.

Zoogloea: Young cells are actively motile. They form later dendritic growth masses attached to solids in both natural waters and sewage.

Fraturia: They are oxidase negative motile or nonmotile organisms, which form yellow to orange colonies. They produce acid from ethyl and other alcohol, aldosugars and sugars and can grow at pH 3.6 and produce H2S. They are ketogenic and do not require organic growth factors.

Species Profiles

P. aeruginosa

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