Rhodobacter capsulatus AnfA is essential for production of Fe ‐nitrogenase proteins but dispensable for cofactor biosynthesis and electron supply

Rhodobacter capsulatus fixes nitrogen from air by a molybdenum ‐dependent and an iron‐only nitrogenase. Here, we present evidence that the transcriptional activator AnfA is required for AnfHDGK production, but dispensable for biosynthesis of the Fe‐only cofactor and electron delivery. AbstractThe photosynthetic α‐proteobacteriumRhodobacter capsulatus reduces and thereby fixes atmospheric dinitrogen (N2) by a molybdenum (Mo) ‐nitrogenase and an iron‐only (Fe)‐nitrogenase. Differential expression of the structural genes of Mo‐nitrogenase (nifHDK) and Fe ‐nitrogenase (anfHDGK) is strictly controlled and activated by NifA and AnfA, respectively. In contrast to NifA ‐binding sites, AnfA‐binding sites are poorly defined. Here, we identified two highly similar AnfA‐binding sites in theR. capsulatus anfH promoter by studying the effects of promoter mutations on in vivo anfH expression and in vitro promoter binding by AnfA. Comparison of the experimentally determinedR. capsulatus AnfA ‐binding sites and presumed AnfA‐binding sites from other α‐proteobacteria revealed a consensus sequence of dyad symmetry, TAC–N6–GTA, suggesting that AnfA proteins bind their target promoters as dimers. Chromosomal replacement of theanfH promoter by thenifH promoter restoredanfHDGK expression and Fe ‐nitrogenase activity in anR.  capsulatus strain lacking AnfA suggesting that AnfA is required for AnfHDGK production, but dispensable for biosynthesis of the iron ‐o...
Source: MicrobiologyOpen - Category: Microbiology Authors: Tags: ORIGINAL ARTICLE Source Type: research