''Pseudomonas fluorescens'' is a common

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 ...

, rod-shaped

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. It belongs to the ''

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able to ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomencla ...

;

16S rRNA 16S rRNA may refer to: * 16S ribosomal RNA 16 S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome ( SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The g ...

analysis as well as phylogenomic analysis has placed ''P. fluorescens'' in the ''P. fluorescens'' group within the genus, CC-BY icon

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to which it lends its name.

General characteristics

''Pseudomonas fluorescens'' has multiple

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 fro ...

. It has an extremely versatile

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cel ...

, and can be found in the soil and in water. It is an

obligate aerobe An obligate aerobe is an organism that requires oxygen to grow. Through cellular respiration, these organisms use oxygen to metabolise substances, like sugars or fats, to obtain energy. In this type of respiration, oxygen serves as the terminal e ...

, but certain strains are capable of using

nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolubl ...

instead of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well ...

as a final

electron acceptor An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Electron acceptors are sometimes mista ...

during

cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

. Optimal temperatures for growth of ''P. fluorescens'' are 25–30° C. It tests positive for the

oxidase test The oxidase test is used to determine if an organism possesses the cytochrome c oxidase enzyme. The test is used as an aid for the differentiation of ''Neisseria'', ''Moraxella'', ''Campylobacter'' and ''Pasteurella'' species (oxidase positive). I ...

. It is also a nonsaccharolytic bacterial species.

Heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

-stable

lipases Lipase ( ) is a family of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually tr ...

and

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the form ...

s are produced by ''P. fluorescens'' and other similar pseudomonads. These

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...

cause milk to spoil, by causing bitterness,

casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins ( αS1, aS2, β, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in human ...

breakdown, and ropiness due to production of

slime Slime may refer to: Biology * Slime mold, a broad term often referring to roughly six groups of Eukaryotes * Biofilm, an aggregate of microorganisms in which cells adhere to each other and/or to a surface * Slimy (fish), also known as the pon ...

and

coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism ...

of proteins.

The name

The word ''Pseudomonas'' means false unit, being derived from the Greek words ''pseudēs'' (

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

: ψευδής – false) and ''monas'' (

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

: ''monas'', from Greek: μονάς – a single unit). The word was used early in the history of

microbiology Microbiology () is the scientific study of microorganisms, those being unicellular (single cell), multicellular (cell colony), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virology, bacteriology, p ...

to refer to

germ Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during embryo ...

s. The

specific Specific may refer to: * Specificity (disambiguation) * Specific, a cure or therapy for a specific illness Law * Specific deterrence, focussed on an individual * Specific finding, intermediate verdict used by a jury in determining the final ...

name ''fluorescens'' refers to the microbe's secretion of a soluble

fluorescent Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

pigment called pyoverdin, which is a type of

siderophore Siderophores (Greek: "iron carrier") are small, high-affinity iron-chelating compounds that are secreted by microorganisms such as bacteria and fungi. They help the organism accumulate iron. Although a widening range of siderophore functions is no ...

Genomics

Notable ''P. fluorescens'' strains SBW25, Pf-5 and PfO-1 have been sequenced, among others. A comparative genomic study (in 2020) analyzed 494 complete genomes from the entire ''Pseudomonas'' genus, with 25 of them being annotated as ''P. fluorescens''. The phylogenomic analysis clearly showed that the 25 strains annotated as ''P. fluorescens'' did not form a monophyletic group. In addition, their Average Nucleotide Identities did not fulfil the criteria of a species, since they were very diverse. It was concluded that ''P. fluorescens'' is not a species in the strict sense, but should be considered as a wider evolutionary group, or a species complex, that includes within it other species too. This finding is in accordance with previous analyses of 107 ''Pseudomonas'' species, using four core 'housekeeping' genes, that consider ''P. fluorescens'' as a relaxed species complex. The ''P. fluorescens'' relaxed evolutionary group that was defined in, on the basis of the genus phylogenomic tree, comprised 96 genomes and displayed high levels of phylogenetic heterogeneity. It comprised many species, such as ''Pseudomonas corrugata, Pseudomonas brassicacearum, Pseudomonas frederiksbergensis, Pseudomonas mandelii, Pseudomonas kribbensis, Pseudomonas koreensis, Pseudomonas mucidolens, Pseudomonas veronii, Pseudomonas antarctica, Pseudomonas azotoformans, Pseudomonas trivialis, Pseudomonas lurida, Pseudomonas azotoformans, Pseudomonas poae, Pseudomonas libanensis, Pseudomonas synxantha'', and ''Pseudomonas orientalis''. The core proteome of the ''P. fluorescens'' group comprised 1396 proteins. The protein count and GC content of the strains of the ''P. fluorescens'' group ranged between 4152 and 6678 (average: 5603) and between 58.7–62% (average: 60.3%), respectively. Another comparative genomic analysis of 71 ''P. fluorescens'' genomes identified eight major subgroups and developed a set of nine genes as markers for classification within this lineage.

Interactions with ''Dictyostelium''

There are two strains of ''Pseudomonas fluorescens'' associated with ''

Dictyostelium discoideum ''Dictyostelium discoideum'' is a species of soil-dwelling amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unicellular ...

.'' One strain serves as a food source and the other strain does not. The main genetic difference between these two strains is a mutation of the global activator gene called gacA. This gene plays a key role in gene regulation; when this gene is mutated in the nonfood bacterial strain, it is transformed into a food bacterial strain.

Biocontrol properties

Some ''P. fluorescens'' strains (CHA0 or Pf-5, for example) present biocontrol properties, protecting the roots of some plant species against parasitic fungi such as ''

Fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

'' or the oomycete ''

Pythium ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'', as well as some phytophagous nematodes. It is not clear exactly how the plant growth-promoting properties of ''P. fluorescens'' are achieved; theories include: * The bacteria might induce systemic resistance in the host plant, so it can better resist attack by a true pathogen. * The bacteria might outcompete other (pathogenic) soil microbes, e.g., by

s, giving a competitive advantage at scavenging for iron. * The bacteria might produce compounds antagonistic to other soil microbes, such as

phenazine Phenazine is an organic compound with the formula (C6H4)2N2. It is a dibenzo annulated pyrazine, and the parent substance of many dyestuffs, such as the toluylene red, indulines, and safranines (and the closely related eurhodines). Phenazine cr ...

-type antibiotics or

hydrogen cyanide Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on an in ...

. To be specific, certain ''P. fluorescens'' isolates produce the secondary metabolite 2,4-diacetylphloroglucinol (2,4-DAPG), the compound found to be responsible for antiphytopathogenic and biocontrol properties in these strains. The ''phl'' gene cluster encodes factors for 2,4-DAPG biosynthesis, regulation, export, and degradation. Eight genes, ''phlHGFACBDE'', are annotated in this cluster and conserved organizationally in 2,4-DAPG-producing strains of ''P. fluorescens''. Of these genes, ''phlD'' encodes a type III polyketide synthase, representing the key biosynthetic factor for 2,4-DAPG production. ''PhlD'' shows similarity to plant chalcone synthases and has been theorized to originate from

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HG ...

. Phylogenetic and genomic analysis, though, has revealed that the entire ''phl'' gene cluster is ancestral to ''P. fluorescens'', many strains have lost the capacity, and it exists on different genomic regions among strains. Some experimental evidence supports all of these theories, in certain conditions; a good review of the topic is written by Haas and Defago. Several strains of ''P. fluorescens'', such as Pf-5 and JL3985, have developed a natural resistance to

ampicillin Ampicillin is an antibiotic used to prevent and treat a number of bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B strepto ...

and

streptomycin Streptomycin is an antibiotic medication used to treat a number of bacterial infections, including tuberculosis, ''Mycobacterium avium'' complex, endocarditis, brucellosis, ''Burkholderia'' infection, plague, tularemia, and rat bite fever. ...

. These antibiotics are regularly used in biological research as a selective pressure tool to promote

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; ho ...

expression. The strain referred to as Pf-CL145A has proved itself a promising solution for the control of invasive zebra mussels and quagga mussels (''

Dreissena ''Dreissena'' is a genus of small freshwater mussels in the family Dreissenidae in the class Bivalvia. They are found attached to firm substrates by threads from underneath the shells and are the only freshwater bivalves to attach to hard substr ...

''). This bacterial strain is an environmental isolate capable of killing >90% of these mussels by intoxication (i.e., not infection), as a result of natural product(s) associated with their cell walls, and with dead Pf-145A cells killing the mussels equally as well as live cells. Following ingestion of the bacterial cells mussel death occurs following lysis and necrosis of the digestive gland and sloughing of stomach epithelium. Research to date indicates very high specificity to zebra and quagga mussels, with low risk of nontarget impact. Pf-CL145A has now been commercialized under the product name Zequanox, with dead bacterial cells as its active ingredient. Recent results showed the production of the

phytohormone Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pa ...

cytokinin Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and lea ...

by ''P. fluorescens'' strain G20-18 to be critical for its biocontrol activity by activating plant resistance.

Medical properties

By culturing ''P. fluorescens'',

mupirocin Mupirocin, sold under the brand name Bactroban among others, is a topical antibiotic useful against superficial skin infections such as impetigo or folliculitis. It may also be used to get rid of methicillin-resistant ''S. aureus'' (MRSA) when ...

(an

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...

) can be produced, which has been found to be useful in treating skin, ear, and eye disorders. Mupirocin free acid and its salts and esters are agents currently used in creams, ointments, and sprays as a treatment of methicillin-resistant ''Staphylococcus aureus'' infection. ''Pseudomonas fluorescens'' demonstrates

hemolytic Hemolysis or haemolysis (), also known by several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in vivo ...

activity, and as a result, has been known to infect blood transfusions. ''Pseudomonas fluorescens'' produces the antibiotic Obafluorin.

Disease

''Pseudomonas fluorescens'' is an unusual cause of disease in humans, and usually affects patients with compromised immune systems (e.g., patients on cancer treatment). From 2004 to 2006, an outbreak of ''P. fluorescens'' in the United States involved 80 patients in six states. The source of the infection was contaminated

heparin Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. Since heparins depend on the activity of antithrombin, they are considered anticoagulants. Specifically it is also used in the treatm ...

ized saline flushes being used with cancer patients. ''Pseudomonas fluorescens'' is also a known cause of

fin rot A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

in fish.

Metabolism

''Pseudomonas fluorescens'' produces

, phenazine

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

, 2,4-diacetylphloroglucinol and the MRSA-active antibiotic

Biodegradation capacities

4-Hydroxyacetophenone monooxygenase is an enzyme found in ''P. fluorescens'' that transforms piceol, NADPH, H+, and O₂ into 4-hydroxyphenyl acetate, NADP+, and H₂O.

References

External links

The Pseudomonas Genome DatabaseType strain of ''Pseudomonas fluorescens'' at Bac''Dive'' – the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q135292 Pseudomonadales Bacteria described in 1886