Burkholderia cepacia: Difference between revisions

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''Burkholderia cepacia'' is capable of growing on over 200 organic compounds.  It is incredibly versatile in this regard.  Of special interest is its ability to use the chlorinated aromatic compound 2,4,5- trichlorophenoxyacetic acid as a source of carbon and energy (4).  This compound is found in many pesticides and herbicides.  Some of ''Burkholderia cepacia’s'' cell structures include polar flagella used for motility and pili used in adhesion.  ''Burkholderia cepacia'' complex species may express one of two flagellin types that differ in size.  Type I is 55 kDa and type II is 45 kDa.  Aside from motility, flagella have also been noted to function in adhesion, the production of biofilms, and in the production of an inflammatory response in an infected host. (2,5)
''Burkholderia cepacia'' is capable of growing on over 200 organic compounds.  It is incredibly versatile in this regard.  Of special interest is its ability to use the chlorinated aromatic compound 2,4,5- trichlorophenoxyacetic acid as a source of carbon and energy (4).  This compound is found in many pesticides and herbicides.  Some of ''Burkholderia cepacia’s'' cell structures include polar flagella used for motility and pili used in adhesion.  ''Burkholderia cepacia'' complex species may express one of two flagellin types that differ in size.  Type I is 55 kDa and type II is 45 kDa.  Aside from motility, flagella have also been noted to function in adhesion, the production of biofilms, and in the production of an inflammatory response in an infected host. (2,5)


The Entner-Doudoroff pathway is an alternative pathway that breaks down glucose into pyruvate and releases ATP. It is utilized by many different bacteria and archaea. This pathway differs from glycolysis by utilizing different enzymes. Glucose is first converted into 6-phosphogluconate through the direct oxidative and phosphorylative pathways. Different enzymes, including 6-phosphogluconate (6PGA) dehydratase and 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase, then enter the pathway, converting one product to the next until pyruvate is formed. ''Burkholderia cepacia,'' or ''Psuedomonas cepacia,'' differs from most other psuedonomads in that it has higher levels of the enzyme 6-phospho-gluconate dehydrogenase (6PGAD). This enzyme is used in a pathway called the pentose shunt (another slower alternative to glycolysis). Thus, higher levels of this enzyme suggest that it has the potential to also utilize the pentose shunt. If one of the enzymes involved in the Entner-Doudoroff pathway was mutated, the pentose shunt would thus be utilized, resulting in a slower growth rate. However, in the event of enzyme mutation, the utilization of the pentose shunt is rarely seen due to a lack of growth. When an enzyme is mutated, it cannot convert one product to the next and the pathway is blocked at this point. This leads to a toxic accumulation of the unconverted product, for example 6PGA, and consequently, no growth occurs. One study, however, observed that certain strains of 6PGA dehydratase deficient mutants produced even more 6PGAD. This reflects the possibility that Entner-Doudoroff mutants may develop enough 6PGAD to overcome the toxic accumulation of 6GPA and utilize the pentose shunt. (15)
The Entner-Doudoroff pathway is an alternative pathway that breaks down glucose into pyruvate and releases ATP. It is utilized by many different bacteria and archaea. This pathway differs from glycolysis by utilizing different enzymes. Glucose is first converted into 6-phosphogluconate through the direct oxidative and phosphorylative pathways. Different enzymes, including 6-phosphogluconate (6PGA) dehydratase and 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase, then enter the pathway, converting one product to the next until pyruvate is formed. ''Burkholderia cepacia,'' or ''Pseudomonas cepacia,'' differs from most other pseudonomads in that it has higher levels of the enzyme 6-phospho-gluconate dehydrogenase (6PGAD). This enzyme is used in a pathway called the pentose shunt (another slower alternative to glycolysis). Thus, higher levels of this enzyme suggest that it has the potential to also utilize the pentose shunt. If one of the enzymes involved in the Entner-Doudoroff pathway was mutated, the pentose shunt would thus be utilized, resulting in a slower growth rate. However, in the event of enzyme mutation, the utilization of the pentose shunt is rarely seen due to a lack of growth. When an enzyme is mutated, it cannot convert one product to the next and the pathway is blocked at this point. This leads to a toxic accumulation of the unconverted product, for example 6PGA, and consequently, no growth occurs. One study, however, observed that certain strains of 6PGA dehydratase deficient mutants produced even more 6PGAD. This reflects the possibility that Entner-Doudoroff mutants may develop enough 6PGAD to overcome the toxic accumulation of 6GPA and utilize the pentose shunt. (15)


==Ecology==
==Ecology==

Revision as of 22:46, 21 April 2010

A Microbial Biorealm page on the genus Burkholderia cepacia

Classification

Higher order taxa

Domain: Bacteria; Phylum: Proteobacteria; Class: Betaprotebacteria; Order: Burkholderiales; Family: Burkholderiaceae; Genus: Burkholderia

Species

NCBI: Taxonomy

The Burkholderia cepacia complex consists of nine genomic species called genomovars: B. cepacia, B. multivorans, B. cenocepacia, B. vietnamiensis, B. stabilis, B. ambifaria, B. dolosa, B. anthina, and B. pyrrocinia.

Description and significance

Burkholderia cepacia was first described by Walter Burkholder of Cornell University in 1949 when he determined it to be the cause of bacterial rot of onion bulbs. It was originally named Pseudomonas cepacia and was later changed to its current name. Burkholderia cepacia refers to a complex of nine closely related species listed above. They are rod-shaped, free-living, motile Gram- negative bacteria ranging from 1.6- 3.2 μm. They have been found to possess multitrichous polar flagella as well as pili used for attachment. Burkholderia cepacia can be found in soil, water, and infected plants, animals, and humans (1). Aside from being a plant and human pathogen it has many significant agricultural uses. It is capable of breaking down toxic compounds found in pesticides and herbicides. It has also been noted to repress certain soil-borne pathogens and is being considered as an agent for promoting crop growth.

The appearance of Burkholderia cepacia species varies based on the strain and the culture medium used. Three media are currently being used to isolate the bacteria. They are the following: Pseudomonas cepacia agar (PCA), oxidation fermentation polymyxin bacitracin lactose agar (OFBL), and Burkholderia cepacia selective agar (BCA). The last medium has proved to be the most effective since it actually suppresses the growth of non-Burkholderia cepacia bacteria. Burkholderia cepacia bacteria will form visible pinpoint colonies within 24 hours, and the colonies appear to be smooth and somewhat elevated.

Genome structure

The replicon number and sizes vary from strain to strain in Burkholderia cepacia species. The largest replicon is found in strain N2P5 (9.3 Mb). Most species contain 2 to 4 large replicons, and many also contain smaller replicons as well. Many species contain plasmids, and all species have circular chromosomes. The Burkholderia cepacia type- strain ATCC 25416 (genomovar I) is 8.1 Mb in length and is known to have four circular replicons. Its largest replicon contains 4 rrn operons and the other two megabase- sized replicons contain a single rrn operon each. From this information it can be inferred that the organism has three chromosomes and one large plasmid. (6)

Cell structure and metabolism

Burkholderia cepacia is capable of growing on over 200 organic compounds. It is incredibly versatile in this regard. Of special interest is its ability to use the chlorinated aromatic compound 2,4,5- trichlorophenoxyacetic acid as a source of carbon and energy (4). This compound is found in many pesticides and herbicides. Some of Burkholderia cepacia’s cell structures include polar flagella used for motility and pili used in adhesion. Burkholderia cepacia complex species may express one of two flagellin types that differ in size. Type I is 55 kDa and type II is 45 kDa. Aside from motility, flagella have also been noted to function in adhesion, the production of biofilms, and in the production of an inflammatory response in an infected host. (2,5)

The Entner-Doudoroff pathway is an alternative pathway that breaks down glucose into pyruvate and releases ATP. It is utilized by many different bacteria and archaea. This pathway differs from glycolysis by utilizing different enzymes. Glucose is first converted into 6-phosphogluconate through the direct oxidative and phosphorylative pathways. Different enzymes, including 6-phosphogluconate (6PGA) dehydratase and 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase, then enter the pathway, converting one product to the next until pyruvate is formed. Burkholderia cepacia, or Pseudomonas cepacia, differs from most other pseudonomads in that it has higher levels of the enzyme 6-phospho-gluconate dehydrogenase (6PGAD). This enzyme is used in a pathway called the pentose shunt (another slower alternative to glycolysis). Thus, higher levels of this enzyme suggest that it has the potential to also utilize the pentose shunt. If one of the enzymes involved in the Entner-Doudoroff pathway was mutated, the pentose shunt would thus be utilized, resulting in a slower growth rate. However, in the event of enzyme mutation, the utilization of the pentose shunt is rarely seen due to a lack of growth. When an enzyme is mutated, it cannot convert one product to the next and the pathway is blocked at this point. This leads to a toxic accumulation of the unconverted product, for example 6PGA, and consequently, no growth occurs. One study, however, observed that certain strains of 6PGA dehydratase deficient mutants produced even more 6PGAD. This reflects the possibility that Entner-Doudoroff mutants may develop enough 6PGAD to overcome the toxic accumulation of 6GPA and utilize the pentose shunt. (15)

Ecology

Burkholderia cepacia complex species are soil-dwelling bacteria commonly found on plant roots. They are of significant environmental interest. Along with their antinematodal and antifungal properties, they can also degrade a large variety of toxic compounds. This makes them extremely useful in bioremediation, a practice using biological compounds to remove hazardous compounds and pollutants. Chlorinated phenols and phenoxyacetates are commonly used in agriculture as pesticides, herbicides, and preservatives. They compose a major group of recalcitrant environmental pollutants. Burkholderia cepacia has the ability to use these compounds as a source of carbon and energy, therefore breaking them down and removing them from the environment (4).

Pathology

Burkholderia cepacia has long been known as both a plant and human pathogen. It was first discovered as a plant pathogen in 1949 when it was found to cause onion rot. In humans it is most well known for its infection in cystic fibrosis patients as well as patients with chronic granulomatous disease and other patients with compromised immune systems. All species within the Burkholderia cepacia complex have been isolated from cystic fibrosis patients, however genomovar III and Burkholderia multivorans seem to cause the majority of infections. (7) There is still much to be learned about the virulence factors used by Burkholderia cepacia. There is evidence that two species, Burkholderia cenocepacia (genomovar III)and the type strain Burkholderia cepacia (genomovar I) actually use quorum sensing to control the expression of their virulence factors, which means their pathogenicity is only expressed when a high enough population density exists to take over the host before it can mount a response. This was recorded of genomovar III in the lungs of cystic fibrosis patients and of genomovar I in onions (8). There is a high mortality rate in patients infected with Burkholderia cepacia. Many develop what is known as cepacia syndrome. This is a fatal necrotizing pneumonia that is currently untreatable.

While infection in patients with cystic fibrosis is most common and extremely detrimental, Burkholderia cepacia can also infect non-cystic fibrosis patients, even non-immunocompromised patients. B. cepacia isolates have been obtained from catheters, wounds, sputum, urine, etc. It can even infect hospital soaps, dextrose solutions, and much more. This means that those individuals working in centers that care for Burkholderia cepacia infected patients are not necessarily safe. Because cross-infection is so prevalent it is important that infected patients be segregated from non-infected patients (13).

The severity of Burkholderia cepacia infection is due in part to its formation of biofilms, which are commonly resistant to antibiotics. The initiation of a biofilm is dependent upon the organism's pili and flagella used for attachment as well as through lateral movement which enlarges the colony. The maturation of the biofilm has been found to depend on the production of the exopolysaccharide cepacian which is known to stabilize the three-dimensional architecture of the biofilm (10). The beginning stages of infection have also been linked to the scavenging of iron. Burkholderia cepacia produces the following four iron-binding siderophores: salicylic acid, ornibactin, pyochelin, and cepabactin. Burkholderia cepacia is also capable of crossing the epithelial barrier by somehow inhibiting the body's natural pulmonary defense mechanisms. Lipopolysaccharides have also been shown to induce an inflammatory response in the lungs of infected patients, allowing infection to become increasingly necrotizing (14).

Application to Biotechnology

Burkholderia cepacia does produce antinematodal and antimicrobial compounds. These compounds protect plants from soil-borne pathogens, and are being proposed for use in place of environmentally harmful pesticides and herbicides. Some of these compounds have been identified as pyrrolnitrin which exerts an inhibitory effect on the electron transport chain (11), pyoluteolin, and the siderophore cepabactin. The production of volatile ammonia has also been found to control soil pathogens (12).

Current Research

The most current research on Burkholderia cepacia includes its use in the agricultural industry to protect plants from pathogens. Burkholderia cepacia can colonize the roots of many plants where it produces compounds that protect against soil-borne pathogens. In absence of these pathogens, plant growth has been noted to improve (9).

Another area of interest for Burkholderia cepacia is in bioremediation because of its ability to metabolize certain toxic and hazardous compounds. This includes 2,4,5- trichlorophenoxyacetic acid, which it the main component of Agent Orange (9).

Current research on Burkholderia cepacia also includes its pathogenicity in immunocompromised patients. Over the last decade or two, Burkholderia cepacia has become an increasingly dangerous threat to cystic fibrosis patients, other immmunocompromised patients, and personnel caring for the infected. Its large genome makes it a strong and versatile microorganism. It is resistant to many antibiotics, and infected patients do not seem to respond to treatment. The eradication of Burkholderia cepacia as a human pathogen will become increasingly important in the years to come (13).

The possibilities of this organism are very exciting as stated in the following quote: "What better microbial challenge to unite agricultural and medical microbiologists than an organism that reduces an onion to a macerated pulp, protects other crops from bacterial and fungal disease, devastates the health and social life of cystic fibrosis patients, and not only is resistant to the most famous of antibiotics, penicillin, but can use it as a nutrient!" (J. R. W. Govan, 1998)

Although these are exciting possibilities, little is known as to how the addition of this species into an open environment would affect its pathogenicity. Care must be taken because Burkholderia cepacia is also a very serious human pathogen.

References

1. Miller SC, LiPuma JJ, Parke JL “Culture based and Non-Growth Dependent Detection of the Burkholderia cepacia complex in Soil Environments” Applied Environmental Microbiology, August 2002

2. Barbara A. Hales, J. Alun W. Morgan, C. Anthony Hart, Craig Winstanley “Variation in Flagellin Genes and Proteins in Burkholderia cepacia”

3. P. Wigley, N. F. Burton “Multiple Chromosomes in Burkholderia cepacia and Burkholderia gladioli and their distribution in clinical and environmental strains of B. cepacia” Journal of Applied Microbiology, Volume 88 Issue 5

4. Department of Microbiology and Immunology, College of Medicine, University of Illinois; “Genes for 2,4,5- Trichlorophenoxyacetic Acid Metabolism in B. cepacia AC1100"

5. Teresa A. Uirban, Adam Griffith, Anastasia M. Torok, Mark E. Smolkin, Jane L. Burns, Joanna B. Goldberg. Infect. Immun. 2004 September. Contribution of Burkholderia cenocepacia Flagella to Infectivity and Inflammation

6. Rodly PD, Romling U, Tummler B. “A Physical genome map of the Burkholderia cepacia type strain” Mol. Microbiology 1995; 17:57-67

7. Andrew McDowell, Eshwar Mahenthiralingam, John E. Moore, Kerstin E. A. Dunbar, A Kevin Webb. “PCR-Based Detection and Identification of Burkholderia cepacia Complex Pathogens in Sputum from Cystic Fibrosis Patients” J Clin Microbiol. 2001 December

8. Shawn Lewenza, Barbara Conway, E. P. Greenberg, Pamela A, Sokol. “Quorum Sensing in Burkholderia cepacia: Identification of the LuxRI Homologs CepRI” Journal of Bacteriology 1999 February 181(3): 748-756

9. Peter A. R. Vandamme "Burkholderia cepacia: Pandora's Box Redefined" BCCM. Edition 9-01. Article 2

10. Monica V. Cuaha, Silvia A. Sousa, Jorge H. Leitao, Leonilde M. Moreira, Paula A. Videira, Isabel Sa-Correia "Studies on the Involvement of the Exopolysaccharide produced by Cystic Fibrosis- Associated Isolates of Burkholderia cepacia Complex in Biofilm Formation and in Persistance of Respiratory Infection" Journal of Microbiology. July 2004. p. 3052-3058. Vol. 42. No.7

11. El-Banna, Winkelmann "Pyrrolnitrin from Burkholderia cepacia: antibiotic activity against fungi and novel activities against streptomycetes" Journal of Applied Microbiology 85 (1), 69–78.

12. Mansour Baligh, Martin A. Delgado, Kenneth E. Conway "Evaluation of Burkholderia cepacia Strains: Root Colonization of Catharanthus roseus and In-Vitro Inhibition of Selected Soil-Borne Fungal Pathogens" Feb. 15,1999 Dept. of Entomology and Plant Pathology

13. A. M. Jones, M. E. Dodd, A. K. Webb "Burkholderia cepacia: current clinical issues, environmental controversies, and ethical dilemnas" European Respiratory Journal. 2001; 17:295-301

14. Georg Maschmeyer, Ulf B. Gobel "217 Strenotrophonomonas maltophila and Burkholderia cepacia Principles and Practices of Infectious Disease pp. 2615-2620

15. Allenza P., Lessie T.G. "Burkholderia cepacia mutants blocked in the Entner-Doudoroff pathway" Journal of Bacteriology. June 1982. p.1340-1347.


Edited by Heather McClendon, student of Rachel Larsen and Kit Pogliano

Edited by Marco Almeda and Akadia Kachaochana, students of M Glogowskiat Loyola University