Pseudomonas is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 validly described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able to colonize a wide range of niches. Their ease of culture in vitro and availability of an increasing number of Pseudomonas strain genome sequences has made the genus an excellent focus for scientific research; the best studied species include P. aeruginosa in its role as an opportunistic human pathogen, the plant pathogen P. syringae, the soil bacterium P. putida, and the plant growth-promoting P. fluorescens, P. lini, P. migulae, and P. graminis.
Pseudomonas fluorescens is a common Gram-negative, rod-shaped bacterium. It belongs to the Pseudomonas genus; 16S rRNA analysis as well as phylogenomic analysis has placed P. fluorescens in the P. fluorescens group within the genus, to which it lends its name.
Pseudomonas putida is a Gram-negative, rod-shaped, saprotrophic soil bacterium.
Pseudomonas aeruginosa is a common encapsulated, Gram-negative, facultatively aerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, P. aeruginosa is a multidrug resistant pathogen recognized for its ubiquity, its intrinsically advanced antibiotic resistance mechanisms, and its association with serious illnesses – hospital-acquired infections such as ventilator-associated pneumonia and various sepsis syndromes.
Pseudomonas fragi is a psychrophilic, Gram-negative bacterium that is responsible for dairy spoilage. Unlike many other members of the genus Pseudomonas, P. fragi does not produce siderophores. Optimal temperature for growth is 30 °C, however it can grow between 0 and 35 °C. Based on 16S rRNA analysis, P. fragi has been placed in the P. chlororaphis group.
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 to opportunistic human pathogens, the molecular taxonomy of the genus is still somewhat unclear.
Pseudomonas syringae is a rod-shaped, Gram-negative bacterium with polar flagella. As a plant pathogen, it can infect a wide range of species, and exists as over 50 different pathovars, all of which are available to researchers from international culture collections such as the NCPPB, ICMP, and others.
Pseudomonas citronellolis is a Gram-negative, bacillus bacterium that is used to study the mechanisms of pyruvate carboxylase. It was first isolated from forest soil, under pine trees, in northern Virginia, United States.
Pseudomonas veronii is a Gram-negative, rod-shaped, fluorescent, motile bacterium isolated from natural springs in France. It may be used for bioremediation of contaminated soils, as it has been shown to degrade a variety of simple aromatic organic compounds. Based on 16S rRNA analysis, P. veronii has been placed in the P. fluorescens group.
Pseudomonas aurantiaca is an orange Gram-negative soil bacterium, originally isolated from the rhizosphere soil of potatoes. It produces di-2,4-diacetylfluoroglucylmethan, which is antibiotically active against Gram-positive organisms. It has shown potential for use as a biocontrol agent against plant-pathogenic microbes. Based on 16S rRNA analysis, P. aurantiaca has been placed in the P. chlororaphis group.
Pseudomonas lundensis is a Gram-negative, rod-shaped bacterium that often causes spoilage of milk, cheese, meat, and fish. Based on 16S rRNA analysis, P. lundensis has been placed in the P. chlororaphis group.
Pseudomonas mucidolens is a Gram-negative, non-sporulating, motile, rod bacterium that causes mustiness in eggs. Based on 16S rRNA analysis, P. mucidolens has been placed in the P. fluorescens group.
Pseudomonas pertucinogena is a Gram-negative, rod-shaped, motile bacterium. It derives its name from the fact that it produces pertucin, a bacteriocin active against phase I organisms of Bordetella pertussis. Based on 16S rRNA analysis, P. pertucinogena has been placed in the P. pertucinogena group, named after this species.
Pseudomonas migulae is a fluorescent, Gram-negative, rod-shaped bacterium isolated from natural mineral waters in France. This bacterium has also been isolated from endophytic tissues of lodgepole pine trees growing on gravel mining sites with potential to perform biological nitrogen fixation and plant growth promotion. Based on 16S rRNA analysis, P. migulae has been placed in the P. fluorescens group.
Pseudomonas gessardii is a fluorescent, Gram-negative, rod-shaped bacterium isolated from natural mineral waters in France. Based on 16S rRNA analysis, P. gessardii has been placed in the P. fluorescens group.
Pseudomonas stutzeri is a Gram-negative soil bacterium that is motile, has a single polar flagellum, and is classified as bacillus, or rod-shaped. While this bacterium was first isolated from human spinal fluid, it has since been found in many different environments due to its various characteristics and metabolic capabilities. P. stutzeri is an opportunistic pathogen in clinical settings, although infections are rare. Based on 16S rRNA analysis, this bacterium has been placed in the P. stutzeri group, to which it lends its name.
The rsmY RNA family is a set of related non-coding RNA genes, that like RsmZ, is regulated by the GacS/GacA signal transduction system in the plant-beneficial soil bacterium and biocontrol model organism Pseudomonas fluorescens CHA0. GacA/GacS target genes are translationally repressed by the small RNA binding protein RsmA. RsmY and RsmZ RNAs bind RsmA to relieve this repression and so enhance secondary metabolism and biocontrol traits.
Rhizobacteria are root-associated bacteria that form symbiotic relationships with many plants. The name comes from the Greek rhiza, meaning root. Though parasitic varieties of rhizobacteria exist, the term usually refers to bacteria that form a relationship beneficial for both parties (mutualism). They are an important group of microorganisms used in biofertilizer. Biofertilization accounts for about 65% of the nitrogen supply to crops worldwide. Rhizobacteria are often referred to as plant growth-promoting rhizobacteria, or PGPRs. The term PGPRs was first used by Joseph W. Kloepper in the late 1970s and has become commonly used in scientific literature. PGPRs have different relationships with different species of host plants. The two major classes of relationships are rhizospheric and endophytic. Rhizospheric relationships consist of the PGPRs that colonize the surface of the root, or superficial intercellular spaces of the host plant, often forming root nodules. The dominant species found in the rhizosphere is a microbe from the genus Azospirillum. Endophytic relationships involve the PGPRs residing and growing within the host plant in the apoplastic space.
2,4-Diacetylphloroglucinol or Phl is a natural phenol found in several bacteria:
Pseudomonas protegens are widespread Gram-negative, plant-protecting bacteria. Some of the strains of this novel bacterial species previously belonged to P. fluorescens. They were reclassified since they seem to cluster separately from other fluorescent Pseudomonas species. P. protegens is phylogenetically related to the Pseudomonas species complexes P. fluorescens, P. chlororaphis, and P. syringae. The bacterial species characteristically produces the antimicrobial compounds pyoluteorin and 2,4-diacetylphloroglucinol (DAPG) which are active against various plant pathogens.
