Tiedje Lab - Projects
Burkholderia
The genus Burkholderia of the Betaproteobacteria was formerly known as the rRNA group II pseudomonads. This genus contains over 30 species, which occupy remarkably diverse ecological niches, ranging from contaminated soils to the respiratory tract of humans. Burkholderia species are generally known as plant pathogens (e.g., bacterial rot of onion) or iniquitous soil bacteria. However, the genus also includes two primary pathogens for humans and animals: B. mallei that causes glanders in horses, mules and donkeys, which may be transmitted to humans from infected animals, and B. pseudomallei, the aetiological agent of melioidosis in humans and animals.
Due to their remarkable metabolic versatility, members of this genus occupy a wide range of ecological niches and can be evidenced in soil, water (both fresh and marine), sediments, and plant and animals. They are exploited for biocontrol, bioremediation and plant growth promotion purposes. Nevertheless, for twenty years Burkholderia species have been associated with nosocomial infection and with patients with cystic fibrosis or granulomatous disease (see below Burkholderia cepacia complex), leading to increased mortality and morbidity among patients worldwide. This latter issue has dramatically hampered large scale applications of those promising bacteria in agriculture for instance, due to obvious safety reasons. More data about the ecology, physiology, pathogenicity, genome organization and evolution of those bacteria are thus needed to establish whether a demarcation may be found between useful and pathogenic Burkholderia species.
References
- Coenye, T. and Vandamme, P. (2003) Diversity and significance of Burkholderia species occupying diverse ecological niches. Environ Microbiol 5(9): 719-729
- Parke, J.L., and Gurian-Sherman, D. (2001) Diversity of the Burkholderia cepacia complex and implications for risk assessment of biological control strains. Annu Rev Phytopathol 39: 225-258
The Burkholderia cepacia complex (Alban Ramette)
The Burkholderia cepacia complex (Bcc) comprises at least nine closely related species which can be correctly identified only by polyphasic taxonomic approaches. Members of the complex are among the most metabolically versatile microorganisms known, growing on more than 200 organic compounds, fix atmospheric N2 and may carry multiple antibiotic resistances. They are involved in important processes such as biodegradation of pollutants, biocontrol of root diseases but some also cause disease in plants, animals and humans. Bcc strains are isolated from very different habitats, including soil, rhizospheres, streams and infected plants, animals and human tissues, especially lungs of cystic fibrosis patients. Bcc strains have large and plastic genomes comprised of multiple (2 to 4) replicons, which is thought to give them their ecological versatility. The rather unique genome structural features together with the broad ecological range make this group an interesting model for comparative genomic studies. Such studies can hopefully provide insight into how closely related members of a bacterial group are successful in so many very different environments.
Typical examples of Bcc are:
B. vietnamiensis strain G4 (R1808) is the best trichloroethene (TCE) co-oxidizing strain yet discovered. TCE and its sister chloroethenes are the most widespread hazardous environmental contaminants in groundwaters. Strain G-4 when grown on toluene or phenol produces an oxygenase that degrades TCE. This strain has been used in at a number of polluted sites to aid clean-up of ground water. Strain G-4 was isolated for its TCE oxidizing ability from an industrial waste treatment facility at Pensacola Naval Air Station, Florida. It has also been shown to be rhizosphere competent. Its genome size is estimated to be 8.5Mb. The B. vietnamiensis species is known for its rhizosphere colonizing ability, including on rice, and its ability to fix N2 gas. It is the third most frequent Bcc species isolated from cystic fibrosis patients. Besides its pollutant degrading ability, this strain was sequenced because well-characterized members of this species come from cystic fibrosis patients' lung, rice rhizosphere and soil, and hence offer the prospect for differentiating traits important to each habitat.
Strain equivalencies ATCC 53617 = G-4
Strain ATCC 17660 (R-18194) was isolated in 1958 from a forest soil in Trinidad and was one the original strains in the famous Stanier et al. (1966) study of pseudomonads where it was described as Pseudomonas multivorans. Previous pulse field gel electrophoresis experiments suggested that ATCC17760 has an atypical small genome size (4.7 Mb in 2 replicons) hence, comparative analysis with other sequenced Bcc genomes would help to understand genome expansion and test the core gene hypothesis for the Bcc group. However, genome sequencing and new pulse field studies now suggests that ATCC 17760 has an 8.5 Mb genome in 3 replicons. ATCC 17760 was also selected because it is in the same phylogenetic cluster as the B. cepacia type strain, an onion pathogen, and the clinical strain J2315, a devastating pathogen in Cystic Fibrosis patients and sequenced by the Sanger Center. Comparative genomic analysis between the later two may help identify genetic determinants that differentiate clinical from environmental isolates. Information as of 2004 suggests that this strain is not a member of any of the nine Bcc species, and is probably a new species, but among the described species, it appears most closely related to B. cepacia.
Strain equivalencies: ATCC 17760 = LMG 6991 = NCIB 9086 = Stanier strain 383.
Burkholderia cenocepacia (formerly Burkholderia cepacia, and before that Pseudomonas cepacia) is a Gram negative bacterium which is ubiquitous in the environment and may cause a number of diseases in plants. Human infection can be caused by B. cepacia, especially in patients with cystic fibrosis and chronic granulomatous disease, and is often fatal. The strain to be sequenced, J2315, is a genomovar III strain of the ET12 lineage, and is the index strain for transmission of this strain among CF patients in the UK. Strain J2315 has been deposited as LMG 16656 in the Belgium Coordinated Collection of Microorganisms.
Useful links:
IBCWG, International Burkholderia cepacia Working Group <http://go.to/cepacia>
Genome sequencing projects:
B. vietnamiensis G4 <http://genome.jgi-psf.org/draft_microbes/bur08/bur08.home.html>
B. cepacia 383 <http://genome.jgi-psf.org/draft_microbes/bur94/bur94.home.html>
B. cenocepacia J2315 <http://www.sanger.ac.uk/Projects/B_cenocepacia/>
B. xenovorans LB400 <http://genome.jgi-psf.org/finished_microbes/burfu/burfu.home.html>
B. pseudomallei <http://www.sanger.ac.uk/Projects/B_pseudomallei/>
