Detection of heme-binding proteins in epidemic strains of Burkholderia cepacia

A panel of 30 previously characterized strains representing five genomovars from the Burkholderia cepacia complex (E. Mahenthiralingam, T. Coenye, J. W. Chung, D. P. Speert, J. R. W. Govan, P. Taylor, and P. Vandamme, J. Clin. Microbiol. 38:910--913, 2000) were examined for their iron protoporphyrin IX-binding ability. These included B. cepacia genomovars I and III and B. stabilis (formerly B. cepacia genomovar IV), B. multivorans (formerly B. cepacia genomovar II), and B. vietnamiensis (formerly B. cepacia genomovar V). Cells were exposed to micro-oxo bisheme of iron protoporphyrin IX (micro-oxo dimers) and examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing, nondenaturing conditions for the presence of heme-binding proteins using tetramethylbenzidine-H(2)O(2) staining. Seven of the 30 strains, each belonging to B. cepacia genomovar III and designated epidemic (in possessing the B. cepacia epidemic strain marker), expressed a 96- to 100-kDa heme-binding protein which was located in the outer membrane. The heme-binding protein of B. cepacia genomovar III epidemic strain C5424 bound iron(III) protoporphyrin IX in both the monomeric and micro-oxo bisheme forms. Cells of all strains grown on Columbia agar bound iron protoporphyrin IX in the micro-oxo bisheme (dimeric) form. There were no statistical differences between the five genomovars, or those possessing the heme-binding protein, in their micro-oxo bisheme-binding ability. Possession of the outer membrane heme-binding protein may be a pathogenicity trait in enabling the bacterium to withstand oxidative stresses in inflammatory exudates in the lung and may aid identification of invasive epidemic strains of B. cepacia.