Iron regulation of the hcnABC genes encoding hydrogen cyanide synthase depends on the anaerobic regulator ANR rather than on the global activator GacA in Pseudomonas Fluorescens CHAO

摘要

Pseudomonas fluorescens CHAO produces hydrogen cyanide (HCN), a secondary metabolite that substantially contributes to this strain's biocontrol ability. Cyanogenesis is induced by oxygen-limiting conditions, but abolished by iron depletion. In P. fluorescens, the anaerobic regulator ANR and the global activator GacA are both required for the maximal expression of the HCN biosynthetic genes hcnABC. The molecular basis of this regulation by ANR and GacA wa investigated under conditions of oxygen and iron limitation. A promoter deletion analysis using a translational hcnA'-lacZ expression by the addition of iron also depended on the presence of ANR and the FNR/ANR box, but not on GacA, suggesting taht in addition to acting a an oxygen-sensitive protein, ANR also responds to iron availability. Expression of the translational hcnA'-lacZ fuxion remained GacA-dependent in hcn promoter mtants that were no longer responsive to ANR, in agreement with earlier evidence for a post-transcriptional regulatory mechanism under GacA control. These data support a model in which cyanogenesis is sequentially activated by ANR at the level of transcription and by components of the GacA network at the level of translation.