Tj. Brickman et al., Transcriptional activation of Bordetella alcaligin siderophore genes requires the AlcR regulator with alcaligin as inducer, J BACT, 183(2), 2001, pp. 483-489
Genetic and biochemical studies have established that Fur and iron mediate
repression of Bordetella alcaligin siderophore system (alc) genes under iro
n-replete nutritional growth conditions. In this study, transcriptional ana
lyses using Bordetella chromosomal alc-lacZ operon fusions determined that
maximal ale gene transcriptional activity under iron starvation stress cond
itions is dependent on the presence of alcaligin siderophore. Mutational an
alysis and genetic complementation confirmed that alcaligin-responsive tran
scriptional activation of Bordetella alcaligin system genes is dependent on
AlcR, a Fur-regulated AraC-like positive transcriptional regulator encoded
within the alcaligin gene cluster. AlcR-mediated transcriptional activatio
n is remarkably sensitive to inducer, occurring at extremely low alcaligin
concentrations. This positive autogenous control circuit involving alcaligi
n siderophore as the inducer for AlcR-mediated transcriptional activation o
f alcaligin siderophore biosynthesis and transport genes coordinates enviro
nmental and intracellular signals for maximal expression of these genes und
er conditions in which the presence of alcaligin in the environment is perc
eived.