Pseudomonas

Template:Short description Template:Automatic taxobox

Pseudomonas is a genus of Gram-negative bacteria belonging to the family Pseudomonadaceae in the class Gammaproteobacteria. The 348 members of the genus<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }} Partial citation, see Parte et al., 2020 for project reference</ref> demonstrate a great deal of metabolic diversity and consequently are able to colonize a wide range of niches and hosts.<ref name=Brock>Template:Cite book</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref name="doi.org">Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Because of their widespread occurrence in water and plant seeds such as dicots, the pseudomonads were observed early in the history of microbiology. The generic name Pseudomonas created for these organisms was defined in rather vague terms by Walter Migula in 1894 and 1900 as a genus of Gram-negative, rod-shaped, and polar-flagellated bacteria with some sporulating species.<ref name=":0">Migula, W. (1894) Über ein neues System der Bakterien. Arb Bakteriol Inst Karlsruhe 1: 235–238.</ref><ref name=migula>Migula, W. (1900) System der Bakterien, Vol. 2. Jena, Germany: Gustav Fischer.</ref> The latter statement was later proved incorrect and was due to refractive granules of reserve materials.<ref name=palleroni>Template:Cite journal</ref> Despite the vague description, the type species, Pseudomonas pyocyanea (basionym of Pseudomonas aeruginosa), proved the best descriptor.<ref name=palleroni/>

Classification historyEdit

Like most bacterial genera, the pseudomonad<ref group=note name=name/> last common ancestor lived hundreds of millions of years ago. They were initially classified at the end of the 19th century when first identified by Walter Migula. The etymology of the name was not specified at the time and first appeared in the seventh edition of Bergey's Manual of Systematic Bacteriology (the main authority in bacterial nomenclature) as Greek pseudes (ψευδής) "false" and -monas (μονάς/μονάδος) "a single unit", which can mean false unit; however, Migula possibly intended it as false Monas, a nanoflagellated protist<ref name=palleroni/> (subsequently, the term "monad" was used in the early history of microbiology to denote unicellular organisms). Soon, other species matching Migula's somewhat vague original description were isolated from many natural niches and, at the time, many were assigned to the genus. However, many strains have since been reclassified, based on more recent methodology and use of approaches involving studies of conservative macromolecules.<ref name="Cornelis">Template:Cite book</ref>

16S rRNA sequence analysis has redefined the taxonomy of many bacterial species.<ref name="Anzai2000">Template:Cite journal</ref> As a result, the genus Pseudomonas includes strains formerly classified in the genera Chryseomonas and Flavimonas.<ref>Template:Cite journal</ref> Other strains previously classified in the genus Pseudomonas are now classified in the genera Burkholderia and Ralstonia.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

In 2020, a phylogenomic analysis of 494 complete Pseudomonas genomes identified two well-defined species (P. aeruginosa and P. chlororaphis) and four wider phylogenetic groups (P. fluorescens, P. stutzeri, P. syringae, P. putida) with a sufficient number of available proteomes.<ref name=Nikolaidis2020>Template:Cite journal</ref> The four wider evolutionary groups include more than one species, based on species definition by the Average Nucleotide Identity levels.<ref>Template:Cite journal</ref> In addition, the phylogenomic analysis identified several strains that were mis-annotated to the wrong species or evolutionary group.<ref name=Nikolaidis2020 /> This mis-annotation problem has been reported by other analyses as well.<ref>Template:Cite journal</ref> In 2021, a broad phylogenomic analysis on this genus led to the reorganization of the species included in Pseudomonas, leading to the creation of several new genera to accommodate some of them.<ref>Template:Cite journal</ref>

GenomicsEdit

In 2000, the complete genome sequence of a Pseudomonas species was determined; more recently, the sequence of other strains has been determined, including P. aeruginosa strains PAO1 (2000), P. putida KT2440 (2002), P. protegens Pf-5 (2005), P. syringae pathovar tomato DC3000 (2003), P. syringae pathovar syringae B728a (2005), P. syringae pathovar phaseolica 1448A (2005), P. fluorescens Pf0-1, and P. entomophila L48.<ref name="Cornelis"/>

By 2016, more than 400 strains of Pseudomonas had been sequenced.<ref name=Koehorst2016>Template:Cite journal</ref> Sequencing the genomes of hundreds of strains revealed highly divergent species within the genus. In fact, many genomes of Pseudomonas share only 50–60% of their genes, e.g. P. aeruginosa and P. putida share only 2971 proteins out of 5350 (or ~55%).<ref name=Koehorst2016 />

By 2020, more than 500 complete Pseudomonas genomes were available in Genebank. A phylogenomic analysis utilized 494 complete proteomes and identified 297 core orthologues, shared by all strains.<ref name=Nikolaidis2020 /> This set of core orthologues at the genus level was enriched for proteins involved in metabolism, translation, and transcription and was utilized for generating a phylogenomic tree of the entire genus, to delineate the relationships among the Pseudomonas major evolutionary groups.<ref name=Nikolaidis2020/> In addition, group-specific core proteins were identified for most evolutionary groups, meaning that they were present in all members of the specific group, but absent in other pseudomonads. For example, several P. aeruginosa-specific core proteins were identified that are known to play an important role in this species' pathogenicity, such as CntL, CntM, PlcB, Acp1, MucE, SrfA, Tse1, Tsi2, Tse3, and EsrC.<ref name=Nikolaidis2020 />

In 2021, a comparative genomic study with more than 3000 Pseudomonas genomes helped to discover genes and functions related with the environmental adaptation of these bacteria.<ref name="doi.org"/>

CharacteristicsEdit

Members of the genus display these defining characteristics:<ref name=Bergey_1984>Template:Cite book</ref>

Rod-shaped
Gram-negative
Flagellum one or more, providing motility
Aerobic
Non-spore forming
Catalase-positive
Oxidase-variable

Other characteristics that tend to be associated with Pseudomonas species (with some exceptions) include secretion of pyoverdine, a fluorescent yellow-green siderophore<ref name="Meyer_2002">Template:Cite journal</ref> under iron-limiting conditions. Certain Pseudomonas species may also produce additional types of siderophore, such as pyocyanin by Pseudomonas aeruginosa<ref name="Lau_2004">Template:Cite journal</ref> and thioquinolobactin by Pseudomonas fluorescens.<ref name="Matthijs_2007">Template:Cite journal</ref> Pseudomonas species also typically give a positive result to the oxidase test, the absence of gas formation from glucose, glucose is oxidised in oxidation/fermentation test using Hugh and Leifson O/F test, beta hemolytic (on blood agar), indole negative, methyl red negative, Voges–Proskauer test negative, and citrate positive.Template:Citation needed

Pseudomonas may be the most common nucleator of ice crystals in clouds, thereby being of utmost importance to the formation of snow and rain around the world.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The genus Pseudomonas is recognized for its remarkable metabolic diversity, enabling it to thrive in a wide range of environments. These bacteria produce a vast array of secondary metabolites,<ref>Template:Cite journal</ref> including antibiotics, siderophores, and biosurfactants, which contribute to their ecological versatility and biotechnological potential.

Biofilm formationEdit

All species and strains of Pseudomonas have historically been classified as strict aerobes. Exceptions to this classification have recently been discovered in Pseudomonas biofilms.<ref name="Hassett_2002">Template:Cite journal</ref> A significant number of cells can produce exopolysaccharides associated with biofilm formation. Secretion of exopolysaccharides such as alginate makes it difficult for pseudomonads to be phagocytosed by mammalian white blood cells.<ref name="Sherris">Template:Cite book</ref> Exopolysaccharide production also contributes to surface-colonising biofilms that are difficult to remove from food preparation surfaces. Growth of pseudomonads on spoiling foods can generate a "fruity" odor.Template:Citation needed

Antibiotic resistanceEdit

Most Pseudomonas spp. are naturally resistant to penicillin and the majority of related beta-lactam antibiotics, but a number are sensitive to piperacillin, imipenem, ticarcillin, or ciprofloxacin.<ref name=Sherris /> Aminoglycosides such as tobramycin, gentamicin, and amikacin are other choices for therapy.Template:Citation needed

This ability to thrive in harsh conditions is a result of their hardy cell walls that contain proteins known as porins. Their resistance to most antibiotics is attributed to efflux pumps, which pump out some antibiotics before they are able to act.Template:Citation needed

Pseudomonas aeruginosa is increasingly recognized as an emerging opportunistic pathogen of clinical relevance. One of its most worrying characteristics is its low antibiotic susceptibility.<ref>Template:Cite journal</ref> This low susceptibility is attributable to a concerted action of multidrug efflux pumps with chromosomally encoded antibiotic resistance genes (e.g., mexAB-oprM, mexXY, etc.<ref>Template:Cite journal</ref>) and the low permeability of the bacterial cellular envelopes. Besides intrinsic resistance, P. aeruginosa easily develops acquired resistance either by mutation in chromosomally encoded genes or by the horizontal gene transfer of antibiotic resistance determinants. Development of multidrug resistance by P. aeruginosa isolates requires several different genetic events that include acquisition of different mutations and/or horizontal transfer of antibiotic resistance genes. Hypermutation favours the selection of mutation-driven antibiotic resistance in P. aeruginosa strains producing chronic infections, whereas the clustering of several different antibiotic resistance genes in integrons favours the concerted acquisition of antibiotic resistance determinants. Some recent studies have shown phenotypic resistance associated to biofilm formation or to the emergence of small-colony-variants, which may be important in the response of P. aeruginosa populations to antibiotic treatment.<ref name="Cornelis"/>

Sensitivity to galliumEdit

Although gallium has no natural function in biology, gallium ions interact with cellular processes in a manner similar to iron(III). When gallium ions are mistakenly taken up in place of iron(III) by bacteria such as Pseudomonas, the ions interfere with respiration, and the bacteria die. This happens because iron is redox-active, allowing the transfer of electrons during respiration, while gallium is redox-inactive.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

PathogenicityEdit

Animal pathogensEdit

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Infectious species include P. aeruginosa, P. oryzihabitans, and P. plecoglossicida. P. aeruginosa flourishes in hospital environments, and is a particular problem in this environment, since it is the second-most common infection in hospitalized patients (nosocomial infections).<ref>Template:Cite journal</ref> This pathogenesis may in part be due to the proteins secreted by P. aeruginosa. The bacterium possesses a wide range of secretion systems, which export numerous proteins relevant to the pathogenesis of clinical strains.<ref name="Hardie">Template:Cite book</ref> Intriguingly, several genes involved in the pathogenesis of P. aeruginosa, such as CntL, CntM, PlcB, Acp1, MucE, SrfA, Tse1, Tsi2, Tse3, and EsrC are core group-specific,<ref name=Nikolaidis2020 /> meaning that they are shared by the vast majority of P. aeruginosa strains, but they are not present in other Pseudomonads.

Plant pathogensEdit

P. syringae is a prolific plant pathogen. It exists as over 50 different pathovars, many of which demonstrate a high degree of host-plant specificity. Numerous other Pseudomonas species can act as plant pathogens, notably all of the other members of the P. syringae subgroup, but P. syringae is the most widespread and best-studied.Template:Citation needed

Fungus pathogensEdit

P. tolaasii can be a major agricultural problem, as it can cause bacterial blotch of cultivated mushrooms.<ref name="Brodey_1991">Template:Cite journal</ref> Similarly, P. agarici can cause drippy gill in cultivated mushrooms.<ref name="Young_1970">Template:Cite journal</ref>

Use as biocontrol agentsEdit

Since the mid-1980s, certain members of the genus Pseudomonas have been applied to cereal seeds or applied directly to soils as a way of preventing the growth or establishment of crop pathogens. This practice is generically referred to as biocontrol. The biocontrol properties of P. fluorescens and P. protegens strains (CHA0 or Pf-5 for example) are currently best-understood, although 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 siderophores giving a competitive advantage at scavenging for iron; the bacteria might produce compounds antagonistic to other soil microbes, such as phenazine-type antibiotics or hydrogen cyanide. Experimental evidence supports all of these theories.<ref>Template:Cite journal</ref>

Other notable Pseudomonas species with biocontrol properties include P. chlororaphis, which produces a phenazine-type antibiotic active agent against certain fungal plant pathogens,<ref>Template:Cite journal</ref> and the closely related species P. aurantiaca, which produces di-2,4-diacetylfluoroglucylmethane, a compound antibiotically active against Gram-positive organisms.<ref>Template:Cite journal</ref>

Use as bioremediation agentsEdit

Some members of the genus are able to metabolise chemical pollutants in the environment, and as a result, can be used for bioremediation. Notable species demonstrated as suitable for use as bioremediation agents include:

P. alcaligenes, which can degrade polycyclic aromatic hydrocarbons.<ref name=O>Template:Cite journal</ref>
P. mendocina, which is able to degrade toluene.<ref name=Yen_1991>Template:Cite journal</ref>
P. pseudoalcaligenes, which is able to use cyanide as a nitrogen source.<ref name=Huertas_2006>Template:Cite journal</ref>
P. resinovorans, which can degrade carbazole.<ref name="Nojiri_2002">Template:Cite journal</ref>
P. aeruginosa, P. putida, P. desmolyticum, and P. nitroreducens can degrade chlorpyrifos.<ref>Template:Cite journal</ref>
P. veronii, which has been shown to degrade a variety of simple aromatic organic compounds.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
P. putida, which has the ability to degrade organic solvents such as toluene.<ref name="Marqués_1993">Template:Cite journal</ref> At least one strain of this bacterium is able to convert morphine in aqueous solution into the stronger and somewhat expensive to manufacture drug hydromorphone (Dilaudid).
Strain KC of P. stutzeri, which is able to degrade carbon tetrachloride.<ref>Template:Cite journal</ref>

Risks associated with pseudomonasEdit

Pseudomonas is a genus of bacteria known to be associated with several diseases affecting humans, plants, and animals.

Humans & AnimalsEdit

One of the most concerning strains of Pseudomonas is Pseudomonas aeruginosa, which is responsible for a considerable number of hospital-acquired infections. Numerous hospitals and medical facilities face persistent challenges in dealing with Pseudomonas infections. The symptoms of these infections are caused by proteins secreted by the bacteria and may include pneumonia, blood poisoning, and urinary tract infections.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Pseudomonas aeruginosa is highly contagious and has displayed resistance to antibiotic treatments, making it difficult to manage effectively. Some strains of Pseudomonas are known to target white blood cells in various mammal species, posing risks to humans, cattle, sheep, and dogs alike.<ref name=Wood2021>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

FishEdit

While Pseudomonas aeruginosa seems to be a pathogen that primarily affects humans, another strain known as Pseudomonas plecoglossicida poses risks to fish. This strain can cause gastric swelling and haemorrhaging in fish populations.<ref name=Wood2021 />

Plants & FungiEdit

Various strains of Pseudomonas are recognized as pathogens in the plant kingdom. Notably, the Pseudomonas syringae family is linked to diseases affecting a wide range of agricultural plants, with different strains showing adaptations to specific host species. In particular, the virulent strain Pseudomonas tolaasii is responsible for causing blight and degradation in edible mushroom species.<ref name=Wood2021 />

Detection of food spoilage agents in milkEdit

One way of identifying and categorizing multiple bacterial organisms in a sample is to use ribotyping.<ref name="Dasen1">Template:Cite journal</ref> In ribotyping, differing lengths of chromosomal DNA are isolated from samples containing bacterial species, and digested into fragments.<ref name="Dasen1" /> Similar types of fragments from differing organisms are visualized and their lengths compared to each other by Southern blotting or by the much faster method of polymerase chain reaction (PCR).<ref name="Dasen1" /> Fragments can then be matched with sequences found on bacterial species.<ref name="Dasen1" /> Ribotyping is shown to be a method to isolate bacteria capable of spoilage.<ref name="Dogan1">Template:Cite journal</ref> Around 51% of Pseudomonas bacteria found in dairy processing plants are P. fluorescens, with 69% of these isolates possessing proteases, lipases, and lecithinases which contribute to degradation of milk components and subsequent spoilage.<ref name="Dogan1" /> Other Pseudomonas species can possess any one of the proteases, lipases, or lecithinases, or none at all.<ref name="Dogan1" /> Similar enzymatic activity is performed by Pseudomonas of the same ribotype, with each ribotype showing various degrees of milk spoilage and effects on flavour.<ref name="Dogan1" /> The number of bacteria affects the intensity of spoilage, with non-enzymatic Pseudomonas species contributing to spoilage in high number.<ref name="Dogan1" />

Food spoilage is detrimental to the food industry due to production of volatile compounds from organisms metabolizing the various nutrients found in the food product.<ref name="Casalinuovo1">Template:Cite journal</ref> Contamination results in health hazards from toxic compound production as well as unpleasant odours and flavours.<ref name="Casalinuovo1" /> Electronic nose technology allows fast and continuous measurement of microbial food spoilage by sensing odours produced by these volatile compounds.<ref name="Casalinuovo1" /> Electronic nose technology can thus be applied to detect traces of Pseudomonas milk spoilage and isolate the responsible Pseudomonas species.<ref name="Magan1">Template:Cite journal</ref> The gas sensor consists of a nose portion made of 14 modifiable polymer sensors that can detect specific milk degradation products produced by microorganisms.<ref name="Magan1" /> Sensor data is produced by changes in electric resistance of the 14 polymers when in contact with its target compound, while four sensor parameters can be adjusted to further specify the response.<ref name="Magan1" /> The responses can then be pre-processed by a neural network which can then differentiate between milk spoilage microorganisms such as P. fluorescens and P. aureofaciens.<ref name="Magan1" />

SpeciesEdit

Pseudomonas comprises the following species,<ref name="LPSN">Template:Lpsn</ref> organized into genomic affinity groups:<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

P. aeruginosa GroupEdit

Template:Div col

P. aeruginosa (Schroeter 1872) Migula 1900 (Approved Lists 1980)
P. citronellolis Seubert 1960 (Approved Lists 1980)
P. delhiensis Prakash et al. 2007
P. denitrificans Bergey et al. 1961
P. jinjuensis Kwon et al. 2003
P. knackmussii Stolz et al. 2007
P. nicosulfuronedens Li et al. 2021
P. nitroreducens Iizuka and Komagata 1964 (Approved Lists 1980)
P. panipatensis Gupta et al. 2008

Pseudomonas

Classification historyEdit

GenomicsEdit

CharacteristicsEdit

Biofilm formationEdit

Antibiotic resistanceEdit

Sensitivity to galliumEdit

PathogenicityEdit

Animal pathogensEdit

Plant pathogensEdit

Fungus pathogensEdit

Use as biocontrol agentsEdit

Use as bioremediation agentsEdit

Risks associated with pseudomonasEdit

Humans & AnimalsEdit

FishEdit

Plants & FungiEdit

Detection of food spoilage agents in milkEdit

SpeciesEdit

P. aeruginosa GroupEdit

P. anguilliseptica GroupEdit

P. fluorescens GroupEdit

P. linyingensis GroupEdit

P. lutea GroupEdit

P. massiliensis GroupEdit

P. oleovorans GroupEdit

P. oryzihabitans GroupEdit

P. pohangensis GroupEdit

P. putida GroupEdit

P. resinovorans GroupEdit

P. rhizosphaerae GroupEdit

P. straminea GroupEdit

P. stutzeri GroupEdit

P. syringae GroupEdit

incertae sedisEdit

Species previously classified in the genusEdit

PhylogeneticsEdit

BacteriophagesEdit

See alsoEdit

FootnotesEdit

ReferencesEdit

External linksEdit

GeneralEdit