Pseudomonas fluorescens
A Microbial Biorealm page on the genus Pseudomonas fluorescens
Classification
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Pseudomonadales; Pseudomonadaceae
Species
Pseudomonas fluorescens
NCBI: Taxonomy |
Description and significance
Pseudomonas fluorescens are Gram-negative rod shaped bacteria that inhabit soil, plants, and water surfaces.(2) The Pf-5 strain resides in the plant’s rhizosphere and produces a variety of secondary metabolites including antibiotics against soilborne plant pathogens.(4) Pseudomonas fluorescens PFO-1 are well adapted to the soil where it was first isolated in agricultural soil.(1) Pseudomonas fluorescens strain SBW25 grows on plant leaves and roots where it can contribute to plant growth. Soluble, green fluorescent pigments are produced when iron concentration is low. The significance of these organisms have increased because of their ability to degrade various pollutants and their use as bio-control against pathogens.(2) Sequencing the genome provided further information of its environmental interaction ands its metabolic capabilities, which can be used against agricultural disease control (1)
Genome structure
Currently, two strains of Pseudomonas fluorescens have the genomes sequenced completely. P. fluorescens Pf-5 genome contains one circular chromosome that has 7.1 Mbp and a GC content of 63.3%. It contains 87 RNAs and 6137 proteins. 5.7% of its genome contributes to secondary metabolism which is the largest of the pseudomonas.(2,4) The genome of Pseudomonas fluorescens PfO-1 has one chromosome with 6.43841 Mbp and 60.5% GC content. There are 95 RNAs and 5736 proteins. The genome sequencing of P. fluorescens SBW25 is still in progress.(2)
Cell structure and metabolism
Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.
P. fluorescens produces viscosin which is a peptidolipid that enhances antivirality. P. fluorescensuses a sulfate transport system that is competitively inhibited by chromate, which may be associated to P. flurorescens's sensitivity to chromate.
Ecology
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
As nonpathogenic bateria, P. fluorescens promote plant growth by producing antibiotics and competing against other plant pathogens.
Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
P. fluorescens produce exopolysaccharides which are used for protection against bacteriophages or dehydration as well as for defense against the host immune system. Polysaccharides are being used within the food, chemical, and agricultural industries. Antibiotics such as pyrrolnitrin, pyoluteorin, and 2,4-diacetylphloroglucinol that inhibit phytopathogen growth are produced by P. fluorescens Pf-5. Diseases from Rhizoctonia solani and Pythium ultimum that affect cotton plants are inhibited by this strain. The bateria's degrading ability has been applied to pollutants such as styrene, TNT and, polycyclic aromatic hydrocarbons(4-6).
Current Research
A copper-transporting P1-type ATPase (CueA) in the genome of Pseudomonas fluorescens SBW25 was investigated for its significance in copper homeostasis and plant colonization. The transcripton of cueA was induced by copper, silver , gold, and mercury ions by using a cueA-lacZ fusion. A nonpolar cueA deletion mutant that reduced its tolerance to copper by twofolds compared to the wild-type strain was also created for this experiment. This mutant did not show any change to its sensitivity to the gold, silver, and mercury ions. Its competitive ability was investigated by placing the mutant strain in three different environments which were a minimal M9 medium, the root of sugar beet (Beta vularis), and the root of pea (Pisum sativum). Change was not observed in the laboratory medium but were seen in the roots. This showed that CueA took part in copper homeostasis and contributed to bacterial fitness. (7)
1-aminocyclopropane-1-carboxylic acid (ACC) deaminase from Pseudomonas fluorescens was studied against saline stress in groundnut (Arachis hypogea) plants under in vitro and field conditions in which four plant growth-promoting rhizobacteria (PGPR) were used. The TDK1 strain was among the four and showed the most improvement in plant growth of the groundnut seedlings under in vitro conditons. Biochemical and moleculat (PCR) analysis showed that strain TDK1 had the greatest ACC deaminase activity so it was isolated, cloned, sequenced, and tested under saline-affected soils in groundnut plants. Results showed improvement in yield even in the presence of saline. Therefore, Pseudomonas fluorescens strain TDK1 that contained ACC deaminase had increased yield by enhancing saline resistance. (8)
Using a universal Chrome Azurol S(CAS)-agar plate method, Pseudomonas florescens strain sp-f was isolated. Due to its nature of siderophore overproduction, experiments were performed to investigate the relationship between siderophores production and its growth. Siderophore production reached a peak during the prophase of logarithmic growth, then was stable during the stationary phase. From RP-HPLC analysis, three kinds of chatecholate siderophores were shown. While the excretion of non-fluorescent pyoverdin siderophores was induced by the 200 micromol/L Fe2+ in the medium, the excretion of fluorescent pyoverdin was completely repressed. (9)
References
1. DOE Joint Genome Institute Pseudomonas fluorescens PfO-1
3. Montie, Thomas. Pseudomonas. New York: Plenum Press, 1998.
6. http://www.ebi.ac.uk/2can/genomes/bacteria/Pseudomonas_syringae.html
Edited by Danielle Kim, student of Rachel Larsen and Kit Pogliano