A Microbial Biorealm page on the genus Hmcclend
Higher order taxa
Bacteria; Proteobacteria; Betaprotebacteria; Burkholderiales; Burkholderiaceae; Burkholderia
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. 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.
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 B. 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 the host. (5)
Application to Biotechnology
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Edited by student of Rachel Larsen and Kit Pogliano