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Journal of Bacteriology, May 2003, p. 3167-3178, Vol. 185, No. 10
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.10.3167-3178.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Energy-Generating Enzymes of Burkholderia cepacia and Their Interactions with Macrophages

Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago, Illinois 60612

Received 10 January 2003/ Accepted 25 February 2003

We previously demonstrated that several clinical and environmental isolates of Burkholderia cepacia secreted ATP-utilizing enzymes to the medium; the secretion of these enzymes by cystic fibrosis lung isolate strain 38 was shown to be greatly enhanced in the presence of ₂-macroglobulin. Fractionation of the growth medium of cystic fibrosis isolate strain 71 belonging to genomovar I demonstrated the presence of two additional proteins, homologues of Pseudomonas aeruginosa azurin and cytochrome c₅₅₁, which are normally involved in electron transfer during denitrification. A Q-Sepharose column flowthrough fraction of the growth medium of B. cepacia strain 71 enriched with the azurin and cytochrome c₅₅₁ homologues triggered apoptosis in macrophages and mast cells, leading to their death. Incubation of the Q-Sepharose column flowthrough fraction with antiazurin and anti-cytochrome c₅₅₁ antibodies greatly reduced cell death. We cloned and hyperexpressed a gene from B. cepacia strain 71 that encodes the homologue of P. aeruginosa azurin. Such azurin homologues were detected in the growth medium of several strains belonging to genomovars I, III, and VI but not in the growth medium of strains belonging to other genomovars. The growth medium of the strains that elaborated the azurin homologue had high cytotoxicity towards macrophages. Purified azurin homologue was shown to induce apoptosis in macrophages in a caspase-dependent manner and was localized in both the cytosol and nucleus when incubated with or microinjected into macrophages. This is an interesting example of the interaction of a bacterial protein normally involved in cellular energetics with macrophages to effect their cell death.