Importance of the Ornibactin and Pyochelin Siderophore Transport Systems in Burkholderia cenocepacia Lung Infections

Abstract

ABSTRACT Previously, orbA , the gene encoding the outer membrane receptor for ferric-ornibactin, was identified in Burkholderia cenocepacia K56-2, a strain which produces ornibactin, salicylic acid, and negligible amounts of pyochelin. A K56-2 orbA mutant was less virulent than the parent strain in a rat agar bead infection model. In this study, an orbA mutant of B. cenocepacia Pc715j which produces pyochelin in addition to ornibactin and salicylic acid was constructed. The gene encoding the outer membrane receptor for ferric-pyochelin ( fptA ) was also identified. An fptA mutant was constructed in Pc715j and shown to be deficient in [ 59 Fe]pyochelin uptake. A 75-kDa iron-regulated protein was identified in outer membrane preparations of Pc715j that was absent in outer membrane preparations of Pc715j fpt A::tp. Pc715j fptA ::tp and Pc715j orbA ::tp produced smaller amounts of their corresponding siderophores. Both Pc715j orbA ::tp and Pc715j fptA ::tp were able to grow in iron starvation conditions in vitro. In the agar bead model, the Pc715j orbA ::tp mutant was cleared from the lung, indicating that the pyochelin uptake system does not compensate for the absence of a functional ornibactin system. Pc715j fptA ::tp persisted in rat lung infections in numbers similar to those of the parent strain, indicating that the ferric-ornibactin uptake system could compensate for the defect in ferric-pyochelin uptake in vivo. These studies suggest that the ornibactin uptake system is the most important siderophore-mediated iron transport system in B. cenocepacia lung infections.