Role of a 21-kDa iron-regulated protein IrpA in the uptake of ferri-exochelin byMycobacterium smegmatis

摘要

Aims To characterize the 21-kDa iron-regulated cell wall protein inMycobacterium smegmatisco-expressed with the siderophores mycobactin, exochelin and carboxymycobactin upon iron limitation. Methods and Results Mycobacterium smegmatis, grown in the presence of 0 center dot 02 mu g Fe ml(-1)(low iron) produced high levels of all the three siderophores, which were repressed in bacteria supplemented with 8 mu g Fe ml(-1)(high iron). Exochelin, the major extracellular siderophore was the first to rise and was expressed at high levels during log phase of growth. Carboxymycobactin, a minor component in log phase iron-starvedM. smegmatiscontinued to rise when cultured for longer periods, reaching levels greater than exochelin. Iron-starved bacteria expressed a 21-kDairon-regulatedprotein (IrpA) that was identified as Clp protease subunit (MSMEG_3671) and characterized as a receptor for ferri-exochelin. Conclusions Ferri-exochelin is the preferred siderophore inM. smegmatisand this ferri-exochelin: IrpA machinery is absent inMycobacterium tuberculosis. Significance and Impact of the Study Exochelin machinery is functional inM. smegmatisand the carboxymycobactin-mycobactin machinery is the sole iron uptake system inM. tuberculosis. The absence of the ferri-exochelin: IrpA system in the pathogen signifies the importance of the carboxymycobactin-mycobactin system machinery inM. tuberculosis.