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O2 availability impacts iron homeostasis in Escherichia coli.

ABSTRACT: The ferric-uptake regulator (Fur) is an Fe2+-responsive transcription factor that coordinates iron homeostasis in many bacteria. Recently, we reported that expression of the Escherichia coli Fur regulon is also impacted by O2 tension. Here, we show that for most of the Fur regulon, Fur binding and transcriptional repression increase under anaerobic conditions, suggesting that Fur is controlled by O2 availability. We found that the intracellular, labile Fe2+ pool was higher under anaerobic conditions compared with aerobic conditions, suggesting that higher Fe2+ availability drove the formation of more Fe2+-Fur and, accordingly, more DNA binding. O2 regulation of Fur activity required the anaerobically induced FeoABC Fe2+ uptake system, linking increased Fur activity to ferrous import under iron-sufficient conditions. The increased activity of Fur under anaerobic conditions led to a decrease in expression of ferric import systems. However, the combined positive regulation of the feoABC operon by ArcA and FNR partially antagonized Fur-mediated repression of feoABC under anaerobic conditions, allowing ferrous transport to increase even though Fur is more active. This design feature promotes a switch from ferric import to the more physiological relevant ferrous iron under anaerobic conditions. Taken together, we propose that the influence of O2 availability on the levels of active Fur adds a previously undescribed layer of regulation in maintaining cellular iron homeostasis.

SUBMITTER: Beauchene NA

PROVIDER: S-EPMC5699043 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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O2 availability impacts iron homeostasis in Escherichia coli.

Beauchene Nicole A NA Mettert Erin L EL Moore Laura J LJ Keleş Sündüz S Willey Emily R ER Kiley Patricia J PJ

Proceedings of the National Academy of Sciences of the United States of America 20171030 46

The ferric-uptake regulator (Fur) is an Fe2+-responsive transcription factor that coordinates iron homeostasis in many bacteria. Recently, we reported that expression of the Escherichia coli Fur regulon is also impacted by O2 tension. Here, we show that for most of the Fur regulon, Fur binding and transcriptional repression increase under anaerobic conditions, suggesting that Fur is controlled by O2 availability. We found that the intracellular, labile Fe< ...[more]

PMID: 29087312

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Project description:The control over iron homeostasis is critical in host-pathogen-interaction. Iron plays not only multiple roles for bacterial growth and pathogenicity, but also for modulation of innate immune responses. Hepcidin is a key regulator of host iron metabolism triggering degradation of the iron exporter ferroportin. Although iron overload in humans is known to increase susceptibility to Burkholderia pseudomallei, it is unclear how the pathogen competes with the host for the metal during infection. This study aimed to investigate whether B. pseudomallei, the causative agent of melioidosis, modulates iron balance and how regulation of host cell iron content affects intracellular bacterial proliferation.Upon infection of primary macrophages with B. pseudomallei, expression of ferroportin was downregulated resulting in higher iron availability within macrophages. Exogenous modification of iron export function by hepcidin or iron supplementation by ferric ammonium citrate led to increased intracellular iron pool stimulating B. pseudomallei growth, whereas the iron chelator deferoxamine reduced bacterial survival. Iron-loaded macrophages exhibited a lower expression of NADPH oxidase, iNOS, lipocalin 2, cytokines and activation of caspase-1. Infection of mice with the pathogen caused a diminished hepatic ferroportin expression, higher iron retention in the liver and lower iron levels in the serum (hypoferremia). In vivo administration of ferric ammonium citrate tended to promote the bacterial growth and inflammatory response, whereas limitation of iron availability significantly ameliorated bacterial clearance, attenuated serum cytokine levels and improved survival of infected mice.Our data indicate that modulation of the cellular iron balance is likely to be a strategy of B. pseudomallei to improve iron acquisition and to restrict antibacterial immune effector mechanisms and thereby to promote its intracellular growth. Moreover, we provide evidence that changes in host iron homeostasis can influence susceptibility to melioidosis, and suggest that iron chelating drugs might be an additional therapeutic option.

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O2 availability impacts iron homeostasis in Escherichia coli.

Publications

O<sub>2</sub> availability impacts iron homeostasis in <i>Escherichia coli</i>.

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