Submitted to: Journal of Bacteriology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2009
Publication Date: 1/1/2010
Publication URL: http://hdl.handle.net/10113/44064
Citation: Jackson, L.A., Ducey, T.F., Zaitshik, J.B., Orvis, J., Dyer, D.W. 2010. Transcriptional and functional analysis of the Neisseria gonorrhoeae fur regulon. Journal of Bacteriology. 192(1):77-85. Interpretive Summary: For a majority of life, iron is an essential nutrient. For bacterial pathogens, such as Neisseria gonorrhoeae, elaborate systems have been designed to scavenge this iron away from the host. For the gonococcus, this system is controlled by the ferric uptake regulator (Fur), which acts as a repressor of iron regulated genes when iron is abundant. This is typically achieved by the ferric uptake regulator protein by binding to a DNA element, called a “ferric uptake regulator box”, within the promoter of regulated genes. This particular study expands the knowledge on the iron response regulon of Neisseria gonorrhoeae, and reveals over 300 genes repressed and 107 genes which increased their expression under iron-replete conditions. Genes which altered their expression ranged from having unknown functions, to iron metabolism, cell communication, cell metabolism, and energy metabolism functions. This report also identified 28 chromosomal segments which interact with ferric uptake regulator via Fur boxes. Four of these segments have been shown to interact in a non-conventional matter, with the Fur box being found as an intragenic element, as opposed to the more common intergenic element. A final aspect of this study also revealed eight potential secondary regulators which may indirectly control aspects of transcription during iron regulation.
Technical Abstract: To ensure survival in the host, bacteria have evolved strategies to acquire the essential element iron. In Neisseria gonorrhoeae, the ferric uptake regulator senses intracellular iron stores and acting as a repressor, directly regulates transcription of iron-responsive genes by binding to a conserved ferric uptake regulator box sequence in the promoter. Our previous studies showed that ferric uptake regulator also controls the transcription of secondary regulators that in turn may control pathways important to pathogenesis, suggesting an indirect role for ferric uptake regulator. To better define the iron-regulated cascade of transcriptional control, we combined three global strategies: temporal transcriptome analysis; genome-wide in silico ferric uptake regulator box prediction; and ferric uptake regulator titration assays to detect genomic regions able to bind ferric uptake regulator in vivo. The majority of the 300 iron-repressed genes were of unknown function followed by iron metabolism, cell communication, and intermediary cell metabolism pathways. The 107 genes up-regulated when iron was present were predominantly hypothetical or genes essential for energy metabolism. Our bioinformatics approach predicted ferric uptake regulator box in 28 ferric uptake regulator titration assay positive clones both in the promoter regions and within the open reading frame of iron-derepressed genes. We also report a decreased conservation at critical thymidine residues involved in ferric uptake regulator binding in the ferric uptake regulator box consensus sequences of the ferric uptake regulator titration assay positive clones with intragenic ferric uptake regulator box consensus sequence compared to the consensus sequence generated from promoter regions. Intragenic ferric uptake regulator box may provide a means of fine tuning the transcriptional response to iron availability. Our findings further indicate that transcription under iron stress is being indirectly controlled by ferric uptake regulator through eight potential secondary regulators.