| To ensure survival, pathogens such as Neisseria gonorrhoeae, must acquire iron. This element is sequestered by the human host in a number of iron-binding ligands. Intracellularly, iron is bound by hemoglobin and ferritin, while transferrin and lactoferrin bind iron extracellularly. This reduces iron levels to a degree that they cannot support bacterial growth, and is termed nutritional immunity. Pathogens however have evolved systems to wrest iron from these human iron-binding ligands. Further, pathogens have evolved complex regulatory systems for responding to changes in iron availability to control iron transport and other functions supporting metabolism and pathogenesis. N. gonorrhoeae expresses a number of receptors which bind directly to, and remove the iron from, these ligands. Expression of these genes have also been demonstrated to be iron repressed, such that when environmental iron levels iron are high, transcription of the genes encoding these receptors is decreased. This repression is controlled by the ferric uptake regulator, which binds to operator sequences in the promoters of these genes termed "Fur boxes". Except for these receptors, information on the gonococcal iron response and the role Fur plays in controlling this response is limited. We have conducted several studies to expand our understanding of the gonococcal iron response. Microarray analysis has determined that roughly 10% of the gonococcal genome (203 genes) is regulated in response to iron availability, and in silico analysis predicted that ∼30% of these genes are directly regulated by Fur. These data also suggest a transcriptional cascade where Fur indirectly controls gene expression by affecting the transcription of three secondary regulators. We also employed a Fur titration assay (FurTA) to specifically examine the role of Fur in the iron response regulon. FurTA identified 26 regions of DNA which interact with the Fur protein via Fur boxes, which correspond to the regulation of 35 genes in response to iron availability. Two FurTA positive clones corresponded to genes containing intragenic Fur boxes, and an additional clone corresponds to a region of DNA which encodes a small RNA which we have designated iasA (iron associated sRNA A) which we hypothesize functions in a manner similar to the iron repressible sRNA of E. coli, ryhB. |
