Abstract
In the nitrogen-fixing heterocyst-forming cyanobacterium Anabaena sp. PCC 7120, the ferric uptake regulator FurA plays a global regulatory role. Failures to eliminate wild-type copies of furA gene from the polyploid genome suggest essential functions. In the present study, we developed a selectively regulated furA expression system by the replacement of furA promoter in the Anabaena sp. chromosomes with the Co2+/Zn2+ inducible coaT promoter from Synechocystis sp. PCC 6803. By removing Co2+ and Zn2+ from the medium and shutting off furA expression, we showed that FurA was absolutely required for cyanobacterial growth. RNA-seq based comparative transcriptome analyses of the furA-turning off strain and its parental wild-type in conjunction with subsequent electrophoretic mobility shift assays and semi-quantitative RT-PCR were carried out in order to identify direct transcriptional targets and unravel new biological roles of FurA. The results of such approaches led us to identify 15 novel direct iron-dependent transcriptional targets belonging to different functional categories including detoxification and defences against oxidative stress, phycobilisome degradation, chlorophyll catabolism and programmed cell death, light sensing and response, heterocyst differentiation, exopolysaccharide biosynthesis, among others. Our analyses evidence novel interactions in the complex regulatory network orchestrated by FurA in cyanobacteria.
Highlights
With only few exceptions, iron is absolutely essential for life of all forms since this metal participates as protein cofactor in major biological processes, such as photosynthesis, respiration, nitrogen fixation, and nucleic acids biosynthesis
We showed that FurA was absolutely required for cyanobacterial growth
We investigate the implication of FurA in less studied cyanobacterial processes such as exopolysaccharide biosynthesis, transposon related function, biosynthesis of the Fe-S cluster, among others
Summary
Iron is absolutely essential for life of all forms since this metal participates as protein cofactor in major biological processes, such as photosynthesis, respiration, nitrogen fixation, and nucleic acids biosynthesis. Aerobic organisms must face a survival paradox: iron is required for growth, but on the other hand, it is potentially toxic due to its ability to catalyze the formation of reactive oxygen species (ROS) by Fenton reactions [1]. Iron became scarce and growth-limiting in most ecological niches, since the predominant form of this micronutrient in nature is extremely insoluble at neutral pH. To cope with this limitation, bacteria have evolved strategies to efficiently scavenge iron from the PLOS ONE | DOI:10.1371/journal.pone.0151384. To cope with this limitation, bacteria have evolved strategies to efficiently scavenge iron from the PLOS ONE | DOI:10.1371/journal.pone.0151384 March 11, 2016
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