TRANSCRIPTIONAL ANALYSIS OF THE BORDETELLA ALCALIGIN SIDEROPHORE BIOSYNTHESIS OPERON

The ale gene cluster of Bordetella pertussis includes three genes, alc A, alcB, and alcC, which are involved in alcaligin siderophore biosynt hesis in response to iron starvation, The production of AlcA, AlcB, an d AlcC in Bordetella cells and the transcriptional organization of alc A, alcB, and alcC were investigated by using a set of three alc'-'lacZ gene fusion constructs that were contiguous with the known promoter u pstream of alcA and extended to fusion junctions within each ale cistr on. All three alc'-'lacZ fusions exhibited iron-repressible reporter g ene expression which was abolished by deletion of the 105-bp alcA prom oter operator region. In an immunoblot analysis using a monoclonal ant ibody specific for beta-galactosidase, the AlcA-LacZ, AlcB-LacZ, and A lcC-LacZ hybrid proteins were detected in Bordetella cells grown under iron-depleted conditions, A B. pertussis mutant in which the 105-bp a lcA promoter-operator region was deleted by allelic exchange was unabl e to produce detectable levels of siderophore. Hybridization analysis using gene-specific probes showed that ale-specific transcript levels in the mutant were negligible compared with those of the wild-type par ent, These results confirm that alcA, alcB, and alcC are cotranscribed from an iron-regulated control region immediately upstream of alcA. T ranscript analysis using hybridization probes representing regions dow nstream of alcC demonstrated that ale transcription extends approximat ely 3.6 kb further downstream from the alcC coding region, suggesting the cotranscription of additional, uncharacterized alcaligin system ge nes.