Burkholderia cepacia: Friend or Foe? Prepared by Jennifer L. Parke, Dept. of Crop and Soil Science, Oregon State University

An extraordinary bacterium
Burkholderia cepacia is a bacterium that is currently attracting considerable attention for its extraordinary versatility as a plant pathogen, saprophyte, biocontrol agent, bioremediation agent, and human pathogen. Formerly known as Pseudomonas cepacia, this bacterium was first described in 1950 as the cause of sour skin of onions by Cornell University plant pathologist Walter Burkholder (1). P. cepacia was recently renamed Burkholderia cepacia (2) and transferred to the beta subdivision of the proteobacteria (3).

B. cepacia is naturally abundant in soil, water, and on plant surfaces (4). It is distinctive in its ability to metabolize a broad range of organic compounds as carbon and energy sources, an attribute which has spurred the development of B. cepacia for use in bioremediation of soil and groundwater contaminated with chlorinated hydrocarbons (5) and herbicides (6). B. cepacia has also been the focus of considerable research by plant pathologists who have shown it to be an effective biocontrol agent against soilborne (7-11), foliar (12), and post-harvest diseases (13-15). Many strains of B. cepacia produce one or more antibiotics active against a broad range of plant pathogenic fungi (16,17). These antibiotics appear, in many cases, to be important for disease suppression. Biocontrol with B. cepacia can be an effective substitute for chemical pesticides which may pose risks to human health and the environment.

B. cepacia the biocontrol agent. Click the image to see an enlarged view. Click here to see other related B. cepacia biocontrol articles from APS Journals.

Three  B. cepacia type Wisconsin strains are registered by the U.S. EPA for use as microbial pesticides (biological control agents). The products include Blue Circle and Deny (Stine Microbial Products). Other strains of B. cepacia are currently being considered by EPA for experimental use permits or registration.

But is B. cepacia safe?
Some scientists are concerned about the use of B. cepacia for biocontrol because certain strains of Burkholderia cepacia are opportunistic human pathogens. B. cepacia is responsible for some nosocomial (hospital-derived) infections, and most alarmingly, some strains can cause fatal lung infection of individuals with cystic fibrosis (CF) (18). Antibiotic treatment is confounded by B. cepacia’s resistance to multiple antibiotics.

B. cepacia the human pathogen. (Photo courtesy J. Govan) Click the image to see an enlarged view.

Cystic fibrosis results from a genetic defect in sodium and chloride transport within epithelial cells, leading to abnormally thick mucus accumulation in the lungs. The mucus clogs the lungs, predisposing patients to chronic and eventually fatal infections by a succession of bacteria including Pseudomonas aeruginosa. (For more information about cystic fibrosis, see http://www.cff.org/factsabo.htm). In the early 1980’s Burkholderia cepacia became associated with epidemics of severe lung infections ("cepacia syndrome") traced, in many cases, to CF treatment centers and social gatherings where CF patients apparently acquired the disease from other B. cepacia-infected individuals (19).

Acquisition of B. cepacia infections from environmental sources has not been ruled out, however. For this reason, the Center for Disease Control recently published an article by Holmes et al.
( http://www.cdc.gov/ncidod/EID/vol4no2/holmes.htm ) calling for a moratorium on the intentional release of B. cepacia in agriculture.

Identifying strains pathogenic to humans
Chief among the concerns is distinguishing between human pathogenic and non-pathogenic strains of B. cepacia. Numerous studies have attempted to separate these strains on the basis of pectinase production, pathogenicity to onion, bacteriocin production and susceptibility, isozyme profiles, and genomic analysis using PFGE and RAPDs (20-25). Vandamme et al. (26) has taken a molecular taxonomic approach for differentiating among the heterogeneous group of strains identified as B. cepacia. They have shown that the B. cepacia complex is comprised of at least 5 distinct genomovars. All of the highly transmissable CF strains belong to genomovar III, but strains representing all five genomovars have been isolated from CF patients and environmental samples. Recent publications demonstrate the potential use of genetic markers to detect highly transmissable CF strains using probes for the cable pilin gene, cblA (27) or for a 1.4 kb fragment called BCESM (B. cepacia epidemic strain marker) (28).

BCESM is associated with 7 epidemic strains, absent among non-epidemic strains, and rare among environmental strains. The development of these promising new methods should aid in the rapid and reliable determination of risk associated with individual B. cepacia strains, and may lead to the discovery of virulence factors responsible for human infection.

An adaptable bacterium
Even if we could identify strains that do not cause human infection, Holmes et al. ( http://www.cdc.gov/ncidod/EID/vol4no2/holmes.htm ) warn that "harmless" strains could evolve quickly into human pathogens. Their concern arises from the observation that isolates of B. cepacia have an unusual capacity to change. B. cepacia has a large and complex genome consisting of 2-4 large replicons (chromosomes), with an overall genome size of 4 to 9 Mb, more than twice the size of E. coli. (29) Click here to see table showing the size and number of replicons for different B. cepacia isolates. B. cepacia also has numerous insertion elements (IS) which promote genomic rearrangements and modify the expression of neighboring genes. This genomic plasticity may contribute to B. cepacia’s remarkable nutritional versatility and evolutionary adaptability, but confounds efforts to predict its behavior in different environments with new selection pressures.

Regulatory issues
EPA is proceeding cautiously on applications for experimental use permits or registration of new B. cepacia strains for biocontrol because of the uncertainties regarding its potential risks (click here for the Phyto News story, "EPA Notice on Microbial Pesticides Concerns"). They have also required label revisions and use restrictions for current registrations. For example, labels of microbial pesticide products that contain B. cepacia are being revised to eliminate or greatly reduce inhalable aerosols and exposure to at-risk populations. Application to turf (previously the only spray application) has been eliminated altogether.

Establishing a dialogue
APS has recognized the need to establish a scientific dialogue about B. cepacia among plant pathologists, medical microbiologists and representatives from regulatory agencies. A symposium, "Burkholderia cepacia: Friend or Foe?", sponsored by the APS Biological Control Committee, will be held at the 1998 APS Annual Meetings in Las Vegas from 1-5 pm on Nov. 9. (Click here to see the symposium agenda.) International experts will offer their insights on the biology, epidemiology, and genetics of this fascinating organism with the goal of developing a knowledge-based approach to evaluating potential risks associated with the use of B. cepacia in agriculture. For more information about this symposium contact co-organizers Jennifer Parke ( Jennifer.Parke@orst.edu ) or Doug Gurian-Sherman ( gurian-sherman.doug@epamail.epa.gov ).

References

1.  Burkholder,W. 1950. Sour skin, a bacterial rot of onion bulbs. Phytopathology 40:115-118.

2.  Yabuuchi, E. Kosako, Y., Oyaizu, H., Yano, I., Hotta, H., Hashimoto, Y. Ezaki, T., and Arakawa, M. 1992. Proposal of Burkholderia gen. nov. and transfer of seven species of the genus Pseudomonas homology group II to the new genus, with the type species Burkholderia cepacia (Palleroni and Holmes, 1981) comb. nov. Microbiol. Immunol. 36:1251-1275.

3.  Olsen, G. J., Woese, C. R., and Overbeek, R. 1994. The winds of (evolutionary) change: breathing new life into microbiology. J. Bacteriol. 176:1-6.

4.  McArthur, J. V., Kovacic, D. A., and Smith, M. H. 1988. Genetic diversity in natural populations of a soil bacterium across a landscape gradient. Proc. Natl. Acad. Sci. USA 85:9621-9624.

5.  Krumme, M. L. Timmis, K. N., and Dwyer, D. F. 1993. Degradation of trichloroethylene by Pseudomonas cepacia G4 and the constitutive mutant strain G4 5223 PR1 in aquifer microcosms. Appl. Environ. Microbiol. 59:2746-2749.

6.  Sangodkar, U. Chapman, P., Chakrabarty, A. 1988. Cloning, physical mapping and expression of chromosomal genes specifiying degradation of the herbicide 2,4,5-T by Pseudomonas cepacia AC1100. Gene 71:267-277.

7.   McLoughlin, T.J. Quinn, J.P. Bettermann, A. Bookland, R. 1992. Pseudomonas cepacia suppression of sunflower wilt fungus and role of antifungal compounds in controlling the disease. Appl. Environ. Microbiol. 58:1760-1763

8.  King, E.B. Parke, J.L. 1993. Biocontrol of Aphanomyces root rot and Pythium damping-off by Pseudomonas cepacia AMMD on four pea cultivars. Plant Dis. 77:1185-1188.

9.   Cartwright, D.K. Benson, D.M. 1995. Comparison of Pseudomonas species and application techniques for biocontrol of Rhizoctonia stem rot of poinsettia. Plant Dis. 79: 309-313.

10. Mao, W. Lewis, J.A. Hebbar, P.K. Lumsden, R.D. 1997. Seed treatment with a fungal or a bacterial antagonist for reducing corn damping-off caused by species of Pythium and Fusarium. [Erratum: July 1997, v. 81 (7), p. 824.] Plant Dis. 81: 450-454.

11.  Milus, E. A. and Rothrock, C. S. 1997. Efficacy of bacterial seed treatments for controlling Pythium root rot of winter wheat. Plant Dis. 81:180-184.

12.  Joy, A. E. and Parke, J. L. 1994. Biocontrol of Alternaria leaf blight on American ginseng by Burkholderia cepacia AMMD. Pages 93-100 in: Challenges of the 21^st century. Proceedings of the International Ginseng Conference, Vancouver, B.C. (Bailey, W. G., Whitehead, C., Proctor, J. T. A., Kyle, J. T., eds.) Simon Fraser Univ., Burnaby, B.C. Canada.

13.  Janisiewicz, W. Yourman, L. Roitman, J. Mahoney, N. 1991. Postharvest control of blue mold and gray mold of apples and pears by dip treatment with pyrrolnitrin, a metabolite of Pseudomonas cepacia. Plant Dis.:490-494.

14.  Smilanick, J.L. Denis-Arrue, R. 1992. Control of green mold of lemons with Pseudomonas species. Plant Dis. 76:481-485.

15.  Smilanick, J.L. Denis-Arrue, R. Bosch, J.R. Gonzalez, A.R., Henson, D. Janisiewicz, W.J. 1993. Control of postharvest brown rot of nectarines and peaches by Pseudomonas species. Crop Prot. 12:513-520.

16.  Roitman, J.N. Mahoney, N.E. Janisiewicz, W.J. 1990. Production and composition of phenylpyrrole metabolites produced by Pseudomonas cepacia. Appl. Microbiol. Biotech. 34:381-386.

17.  Rosales, A. M., Thomashow, L., Cook, R. J., and Mew, T. W. 1995. Isolation and identification of antifungal metabolites produced by rice-associated antagonistic Pseudomonas spp. Phytopathology 85:1028-1032.

18.  Govan, J., Hughes, J., Vandamme, P. 1996. Burkholderia cepacia: medical, taxonomic, and ecological issues. J. Med. Microbiol. 45:395-407.

19.  Govan, J., Brown, P., Maddison, J., Doherty, C., Nelson, J., Dodd, M. et al. 1993. Evidence for transmission of Pseudomonas cepacia by social contact in cystic fibrosis. Lancet 342:15-19.

20.  Gonzalez, C.F. Pettit, E.A. Valadez, V.A. Provin, E.M. 1997. Mobilization, cloning, and sequence determination of a plasmid-encoded polygalacturonase from a phytopathogenic Burkholderia (Pseudomonas) cepacia. MPMI 10:840-851.

21.  Fisher, M. C., LiPuma, J. J., Dasen, S. E., Caputo, G. C., Mortensen, J. E., McGowan, K. L., and Stull, T. L. 1993. Source of Pseudomonas cepacia: ribotyping of isolates from patients and from the environment. J. Pediatr. 123:745-747.

22. Yohalem, D. S. and Lorbeer, J. W. 1994. Intraspecific metabolic diversity among strains of Burkholderia cepacia isolated from decayed onions, soils, and the clinical environment. Antonie van Leewenhoek 65:111-131.

23. Govan, J. R. and Harris, G. 1985. Typing of Pseudomonas cepacia by bacteriocin susceptibility and production. J. Clin. Microbiol. 4:490-494.

24.  Butler, S. L., Doherty, C. J., Hughes, J. E., Nelson, J. W., and Govan, J. R. 1995. Burkholderia cepacia and cystic fibrosis: do natural environments present a potential hazard? J. Clin. Microbiol. 4:1001-1004.

25.  Mahenthiralingam, E., Campbell, M. E., Henry, D. A., and Speert, D. P. 1996. Epidemiology of Burkholderia cepacia infection in patients with cystic fibrosis: analysis by random amplified polymorphic DNA (RAPD) fingerprinting. J. Clin. Microbiol. 34:2914-2920.

26. Vandamme, P., Holmes, B., Vancanneyt, M., Coenye, T., Hoste, B., Coopman, R., et al. 1997. Occurrence of multiple genomovars of Burkholderia cepacia in cystic fibrosis patients and proposal of Burkholderia multivorans sp. nov. Int. J. Syst. Bacteriol. 47:1188-1200.

27.  Sajjan, U. S., Sun, L., Goldstein, R., and Forstner, J. F. 1995. Cable (Cbl) type II pili of cystic fibrosis-associated Burkholderia (Pseudomonas) cepacia: nucleotide sequence of the cblA major subunit pilin gene and novel morphology of the assembled appendage fibers. J. Bacteriol. 177:1030-1038.

28.  Mahenthiralingam, E., Simpson, D. A., and Speert, D. P. 1997. Identification and characterization of a novel DNA marker associated with epidemic Burkholderia cepacia strains recovered from patients with cystic fibrosis. J. Clin. Microbiol. 35:808-816.

29.  Lessie, T. G., Hendrickson, W., Manning, B. D., Devereux, R.. 1996. Genomic complexity and plasticity of Burkholderia cepacia. FEMS Microbiol Letters 144:117-128.

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