PSEUDOMONAS

'''Pseudomonas''' is a genus of gamma proteobacteria, belonging to the larger family of pseudomonads.
Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. Phylogenetic affiliation of the pseudomonads based on 16S rRNA sequence, Anzai Y, Kim H, Park, JY, Wakabayashi H, , , Int J Syst Evol Microbiol, 2000 As a result the genus ''Pseudomonas'' includes strains formerly classifed in the genera ''Chryseomonas'' and ''Flavimonas''.^[1] Other strains previously classified in the genus ''Pseudomonas'' are now classified in the genera ''Burkholderia'' and ''Ralstonia''.

Contents

History

Characteristics

Biofilm formation

Antibiotic resistance

Pathogenicity

Animal pathogens

Plant pathogens

Use as biocontrol agents

Use as bioremediation agents

Food spoilage agents

Species previously classified in the genus ''Pseudomonas''

References

See Also

External links

General

History

''Pseudomonad'' literally means 'false unit', being derived from the Greek ''pseudo'' ('''ψευδο''' 'false') and ''monas'' ('''μονος''' 'a single unit'). The term "monad" was used in the early history of microbiology to denote single-celled organisms.

Characteristics

Members of the genus display the following defining characteristics: Bergey's Manual of Systematic Bacteriology, Volume 1, , Noel, Krieg, Williams & Wilkins, 1984,

★ Rod shaped

★ Gram-negative

★ One or more polar flagella, providing motility

★ Aerobic

★ Non spore forming

★ Positive catalase test
Other characteristics which tend to be associated with ''Pseudomonas'' species (with some exceptions) include secretion of pyoverdin (fluorescein), a fluorescent yellow-green siderophore Siderophore typing, a powerful tool for the identification of fluorescent and nonfluorescent pseudomonads, Meyer JM, Geoffroy VA, Baida N, ''et al'', , , Appl. Environ. Microbiol., 2002 under iron-limiting conditions. Certain ''Pseudomonas'' species may also produce additional types of siderophore, such as pyocyanin by ''Pseudomonas aeruginosa'' The role of pyocyanin in Pseudomonas aeruginosa infection, Lau GW, Hassett DJ, Ran H, Kong F, , , Trends in molecular medicine, 2004 and thioquinolobactin by ''Pseudomonas fluorescens'', Thioquinolobactin, a Pseudomonas siderophore with antifungal and anti-Pythium activity, Matthijs S, Tehrani KA, Laus G, Jackson RW, Cooper RM, Cornelis P, , , Environ. Microbiol., 2007 . ''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, hemolytic (on blood agar), indole negative, methyl red negative, Voges Proskauer test negative.
The genus demonstrates a great deal of metabolic diversity, and consequently are able to colonise a wide range of niches Brock Biology of Microorganisms, Madigan M; Martinko J (editors)., , , Prentice Hall, 2005, ISBN 0131443291 . 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''.

Biofilm formation

All species and strains of ''Pseudomonas'' are Gram-negative rods, and have historically been classified as strict aerobes. Exceptions to this classification have recently been discovered in ''Pseudomonas'' biofilms Anaerobic metabolism and quorum sensing by ''Pseudomonas aeruginosa'' biofilms in chronically infected cystic fibrosis airways: rethinking antibiotic treatment strategies and drug targets, Hassett D, Cuppoletti J, Trapnell B, Lymar S, Rowe J, Yoon S, Hilliard G, Parvatiyar K, Kamani M, Wozniak D, Hwang S, McDermott T, Ochsner U, , , Adv Drug Deliv Rev, 2002 . A significant number can produce exopolysaccharides that are known as slime layers. Secretion of exopolysaccharide makes it difficult for Pseudomonads to be phagocytosed by mammalian white blood cells. Sherris Medical Microbiology, Ryan KJ; Ray CG (editors), , , McGraw Hill, 2004, ISBN 0838585299 Slime production also contributes to surface-colonising biofilms which are difficult to remove from food preparation surfaces. Growth of Pseudomonads on spoiling foods can generate a "fruity" odor.
''Pseudomonas'' have the ability to metabolise a variety of diverse nutrients. Combined with the ability to form biofilms, they are thus able to survive in a variety of unexpected places. For example, they have been found in areas where pharmaceuticals are prepared. A simple carbon source, such as soap residue or cap liner-adhesives is a suitable place for the Pseudomonads to thrive. Other unlikely places where they have been found include antiseptics such as quaternary ammonium compounds and bottled mineral water.

Antibiotic resistance

Being Gram-negative bacteria, most ''Pseudomonas spp.'' are naturally resistant to penicillin and the majority of related beta-lactam antibiotics, but a number are sensitive to piperacillin, imipenem, tobramycin, or ciprofloxacin.
This ability to thrive in harsh conditions is a result of their hardy cell wall that contains porins. Their resistance to most antibiotics is attributed to efflux pumps called ABC transporters, which pump out some antibiotics before they are able to act.

Pathogenicity

Animal pathogens

''P. aeruginosa'' is an opportunistic human pathogen, most commonly affecting immunocompromised patients, such as those with cystic fibrosis Pseudomonal infection in cystic fibrosis: the battle continues, Elkin S, Geddes D, , , Expert review of anti-infective therapy, 2003 or AIDS. Septicaemia in patients with AIDS, Shanson DC, , , Trans. R. Soc. Trop. Med. Hyg., 1990 Infection can affect many different parts of the body, but infections typically target the respiratory tract, causing bacterial pneumonia. Treatment of such infections can be difficult due to multiple antibiotic resistance. Resistance in nonfermenting gram-negative bacteria: multidrug resistance to the maximum, McGowan JE, , , Am. J. Med., 2006
''P. oryzihabitans'' can also be a human pathogen, although infections are rare. It can cause peritonitis, Peritonitis with multiple rare environmental bacteria in a patient receiving long-term peritoneal dialysis, Levitski-Heikkila TV, Ullian ME, , , Am. J. Kidney Dis., 2005 endophthalmitis, Chronic postoperative endophthalmitis due to Pseudomonas oryzihabitans, Yu EN, Foster CS, , , Am. J. Ophthalmol., 2002 septicemia and bacteremia. Similar symptoms although also very rare can be seen by infections of ''P. luteola''. Two new species of ''Pseudomonas'': ''P. oryzihabitans'' isolated from rice paddy and clinical specimens and ''P. luteola'' isolated from clinical specimens., Kodama K, Kimura Nm Komagata K, , , Int J Syst Bacteriol, 1985
''P. plecoglossicida'' is a fish pathogenic species, causing hemorrhagic ascites in the ayu (''Plecoglossus altivelis''). Pseudomonas plecoglossicida sp. nov., the causative agent of bacterial haemorrhagic ascites of ayu, Plecoglossus altivelis, Nishimori E, Kita-Tsukamoto K, Wakabayashi H, , , Int. J. Syst. Evol. Microbiol., 2000 ''P. anguilliseptica'' is also a fish pathogen. Existence of two O-serotypes in the fish pathogen Pseudomonas anguilliseptica, López-Romalde S, Magariños B, Ravelo C, Toranzo AE, Romalde JL, , , Vet. Microbiol., 2003
Due to their hemolytic activity, even non-pathogenic species of ''Pseudomonas'' can occasionally become a problem in clinical settings, where they have been known to infect blood transfusions. Pseudomonas fluorescens bacteremia from blood transfusion, Khabbaz RF, Arnow PM, Highsmith AK, ''et al'', , , Am. J. Med., 1984

Plant pathogens

''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. There are numerous other ''Pseudomonas'' species that 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.
Although not strictly a plant pathogen, ''P. tolaasii'' can be a major agricultural problem, as it can cause bacterial blotch of cultivated mushrooms. Bacterial blotch disease of the cultivated mushroom is caused by an ion channel forming lipodepsipeptide toxin., Brodey CL, Rainey PB, Tester M, Johnstone K, , , Molecular Plant–Microbe Interaction, 1991 . Similarly, ''P. agarici'' can cause drippy gill in cultivated mushrooms. Drippy gill: a bacterial disease of cultivated mushrooms caused by ''Pseudomonas agarici'' n. sp., Young JM, , , NZ J Agric Res, 1970

Use as biocontrol agents

Since the mid 1980s, certain members of the ''Pseudomonas'' genus 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'' 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: that the bacteria might induce systemic resistance in the host plant, so it can better resist attack by a true pathogen; the bacteria might out compete 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. There is experimental evidence to support all of these theories, in certain conditions; a good review of the topic is written by Haas and Defago^[2].
Other notable ''Pseudomonas'' species with biocontrol properties include ''P. chlororaphis'' which produces a phenazine type antibiotic active agent against certain fungal plant pathogens^[3], and the closely related species ''P. aurantiaca'' which produces di-2,4-diacetylfluoroglucylmethan, a compound antibiotically active against Gram-positive organisms^[4].

Use as bioremediation agents

Some members of the genus ''Pseudomonas'' 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. The use of ozone in the remediation of polycyclic aromatic hydrocarbon contaminated soil, O'Mahony MM, Dobson AD, Barnes JD, Singleton I, , , Chemosphere, 2006

★ ''P. mendocina'', which is able to degrade toluene. Cloning and characterization of a Pseudomonas mendocina KR1 gene cluster encoding toluene-4-monooxygenase, Yen KM, Karl MR, Blatt LM, ''et al'', , , J. Bacteriol., 1991

★ ''P. pseudoalcaligenes'' is able to use cyanide as a nitrogen source. Cyanide metabolism of Pseudomonas pseudoalcaligenes CECT5344: role of siderophores, Huertas MJ, Luque-Almagro VM, Martínez-Luque M, ''et al'', , , Biochem. Soc. Trans., 2006

★ ''P. resinovorans'' can degrade carbazole. Organization and transcriptional characterization of catechol degradation genes involved in carbazole degradation by Pseudomonas resinovorans strain CA10, Nojiri H, Maeda K, Sekiguchi H, ''et al'', , , Biosci. Biotechnol. Biochem., 2002

★ ''P. veronii'' has been shown to degrade a variety of simple aromatic organic compounds.^[5][6]

★ ''P. putida'' has the ability to degrade organic solvents such as toluene. Transcriptional control of the Pseudomonas putida TOL plasmid catabolic pathways, Marqués S, Ramos JL, , , Mol. Microbiol., 1993

★ Strain KC of ''P. stutzeri'' is able to degrade carbon tetrachloride.^[7]

Food spoilage agents

As a result of their metabolic diversity, ability to grow at low temperatures and ubiquitous nature, many ''Pseudomonas'' can cause food spoilage. Notable examples include dairy spoilage by ''P. fragi'',^[8] mustiness in eggs caused by ''P. taetrolens'' and ''P. mudicolens'',^[9] and ''P. lundensis'', which causes spoilage of milk, cheese, meat, and fish.^[10]

Species previously classified in the genus ''Pseudomonas''

Recently, 16S rRNA sequence analysis redefined the taxonomy of many bacterial species previously classified as being in the ''Pseudomonas'' genus. Phylogenetic affiliation of the pseudomonads based on 16S rRNA sequence, Anzai Y, Kim H, Park, JY, Wakabayashi H, , , Int J Syst Evol Microbiol, 2000 Species which moved from the ''Pseudomonas'' genus are listed below; clicking on a species will show its new classification. Note that the term 'Pseudomonad' does not apply strictly to just the ''Pseudomonas'' genus, and can be used to also include previous members such as the genera ''Burkholderia'' and ''Ralstonia''.
'α proteobacteria:' ''P. abikonensis'', ''P. aminovorans'', ''P. azotocolligans'', ''P. carboxydohydrogena'', ''P. carboxidovorans'', ''P. compransoris'', ''P. diminuta'', ''P. echinoides'', ''P. extorquens'', ''P. lindneri'', ''P. mesophilica'', ''P. paucimobilis'', ''P. radiora'', ''P. rhodos'', ''P. riboflavina'', ''P. rosea'', ''P. vesicularis''.
'β proteobacteria:' ''P. acidovorans'', ''P. alliicola'', ''P. antimicrobica'', ''P. avenae'', ''P. butanovorae'', ''P. caryophylli'', ''P. cattleyae'', ''P. cepacia'', ''P. cocovenenans'', ''P. delafieldii'', ''P. facilis'', ''P. flava'', ''P. gladioli'', ''P. glathei'', ''P. glumae'', ''P. graminis'', ''P. huttiensis'', ''P. indigofera'', ''P. lanceolata'', ''P. lemoignei'', ''P. mallei'', ''P. mephitica'', ''P. mixta'', ''P. palleronii'', ''P. phenazinium'', ''P. pickettii'', ''P. plantarii'', ''P. pseudoflava'', ''P. pseudomallei'', ''P. pyrrocinia'', ''P. rubrilineans'', ''P. rubrisubalbicans'', ''P. saccharophila'', ''P. solanacearum'', ''P. spinosa'', ''P. syzygii'', ''P. taeniospiralis'', ''P. terrigena'', ''P. testosteroni''.
'γ-β proteobacteria:' ''P. beteli'', ''P. boreopolis'', ''P. cissicola'', ''P. geniculata'', ''P. hibiscicola'', ''P. maltophilia'', ''P. pictorum''.
'γ proteobacteria:' ''P. beijerinckii'', ''P. diminuta'', ''P. doudoroffii'', ''P. elongata'', ''P. flectens'', ''P. halodurans'', ''P. halophila'', ''P. iners'', ''P. marina'', ''P. nautica'', ''P. nigrifaciens'', ''P. pavonacea'', ''P. piscicida'', ''P. stanieri''.
'δ proteobacteria:' ''P. formicans''.

References

1. The phylogeny of the genera ''Chryseomonas'', ''Flavimonas'', and ''Pseudomonas'' supports synonymy of these three genera, , , , Int J Syst Bacteriol, 1997
2. Biological control of soil-borne pathogens by fluorescent pseudomonads, Haas D, Defago G, , , Nature Reviews in Microbiology, 2005
3. Root colonization by phenazine-1-carboxamide-producing bacterium ''Pseudomonas chlororaphis'' PCL1391 is essential for biocontrol of tomato foot and root rot., Chin-A-Woeng TF, ''et al.'', , , Mol Plant Microbe Interact, 2000
4. New antibiotically active fluoroglucide from ''Pseudomonas aurantiaca'', Esipov, ''et al.'', , , Antibiotiki, 1975
5. A novel catabolic activity of ''Pseudomonas veronii'' in biotransformation of pentachlorophenol, Nam, ''et al.'', , , Applied Microbiology and Biotechnology, 2003
6. Degradation of alkyl methyl ketones by ''Pseudomonas veronii'', Onaca, ''et al.'', , , Journal of Bacteriology, 2007 Mar 9
7. Generation and initial characterization of ''Pseudomonas stutzeri'' KC mutants with impaired ability to degrade carbon tetrachloride, Sepulveda-Torres, ''et al.'', , , Arch Microbiol, 1999
8. Nutrition and physiology of ''Pseudomonas fragi'', Pereira, JN, and Morgan, ME, , , J Bacteriol, 1957 Dec
9. Two New Species of Bacteria Causing Mustiness in Eggs, Levine, M, and Anderson, DQ, , , J Bacteriol, 1932 Apr
10. A study of the incidence of different fluorescent ''Pseudomonas'' species and biovars in the microflora of fresh and spoiled meat and fish, raw milk, cheese, soil and water, Gennari, M, and Dragotto, F, , , J Appl Bacteriol, 1992 Apr

See Also

★ Pseudomonas phage Φ6

External links

General

★ Pseudomonas survive in nuclear reactor

★ ''Pseudomonas'' genome database