Phenotypic comparison between rhizosphere and clinical isolates of Burkholderia cepacia

The phenotypic characteristics of four Burkholderia cepacia strains isolated from the rhizosphere and the clinical environment were compared. Tests included optimum growth temperature, utilization of carbon sources, production of HCN, indole-3-acetic acid (IAA) and siderophores, proteolytic activity, nitrogen fixation, inhibition of some phytopathogenic fungi, adherence to human mucosal and plant root epithelia, and greenhouse-based plant-growth promotion experiments using cucumber (Cucumis sativus). Results indicated that the strains of B. cepacia isolated from the rhizosphere differ markedly from their clinical counterparts. Strains isolated from the rhizosphere grew over a wider temperature range, fixed nitrogen and produced IAA, did not produce proteases, displayed a wider antibiosis against the phytopathogenic fungi studied, did not adhere to human uroepithelial cells, promoted growth of C. sativus and only produced a hydroxamate-like siderophore. In contrast, clinical isolates could not fix nitrogen or produce IAA, produced proteases, adhered to human uroepithelial cells, did not promote the growth of C. sativus and, in addition to a hydroxamate-like siderophore, produced pyochelin and salicylate siderophores. All four isolates exhibited the ability to adhere to the root tissue of C. sativus and were unable to produce HCN.