Campylobacter jejuni gene expression in response to iron limitation and the role of Fur

Abstract

Campylobacter jejuni is a zoonotic pathogen and the most common cause of bacterial foodborne diarrhoeal illness worldwide. To establish intestinal colonization prior to either a commensal or pathogenic interaction with the host, C. jejuni will encounter iron-limited niches where there is likely to be intense competition from the host and normal microbiota for iron. To gain a better understanding of iron homeostasis and the role of ferric uptake regulator (Fur) in iron acquisition in C. jejuni, a proteomic and transcriptome analysis of wild-type and fur mutant strains in iron-rich and iron-limited growth conditions was carried out. All of the proposed iron-transport systems for haemin, ferric iron and enterochelin, as well as the putative iron-transport genes p19, Cj1658, Cj0177, Cj0178 and cfrA, were expressed at higher levels in the wild-type strain under iron limitation and in the fur mutant in iron-rich conditions, suggesting that they were regulated by Fur. Genes encoding a previously uncharacterized ABC transport system (Cj1660–Cj1663) also appeared to be Fur regulated, supporting a role for these genes in iron uptake. Several promoters containing consensus Fur boxes that were identified in a previous bioinformatics search appeared not to be regulated by iron or Fur, indicating that the Fur box consensus needs experimental refinement. Binding of purified Fur to the promoters upstream of the p19, CfrA and CeuB operons was verified using an electrophoretic mobility shift assay (EMSA). These results also implicated Fur as having a role in the regulation of several genes, including fumarate hydratase, that showed decreased expression in response to iron limitation. The known PerR promoters were also derepressed in the C. jejuni Fur mutant, suggesting that they might be co-regulated in response to iron and peroxide stress. These results provide new insights into the effects of iron on metabolism and oxidative stress response as well as the regulatory role of Fur.