Abstract
Escherichia coli is a well‐studied bacterium that can be found in many niches, such as industrial wastewater, where the concentration of nickel can rise to low‐millimolar levels. Recent studies show that nickel exposure can repress pyochelin or induce pyoverdine siderophore production in Pseudomonas aueroginosa. Understanding the molecular cross‐talk between siderophore production, metal homeostasis, and metal toxicity in microorganisms is critical for designing bioremediation strategies for metal‐contaminated sites. Here, we show that high‐nickel exposure prolongs lag phase duration as a result of low‐intracellular iron levels in E. coli. Although E. coli cells respond to low‐intracellular iron during nickel stress by maintaining high expression of iron uptake systems such as fepA, the demand for iron is not met due to a lack of siderophores in the extracellular medium during nickel stress. Taken together, these results indicate that nickel inhibits iron accumulation in E. coli by reducing the presence of enterobactin in the extracellular medium.
Highlights
Siderophores are small molecules with high affinity for ferric iron and are produced by bacteria under iron-limiting conditions (Matthew, Jenul, Carlier, & Eberl, 2016; Neilands, 1995)
The amount of nickel exposure can proportionally affect the relative growth of E. coli cells over time in iron-limited media
The lag phase duration of cells exposed to 50 μM nickel chloride is approximately 10-fold longer than cells that were not exposed to nickel stress (Figure 1b)
Summary
Siderophores are small molecules with high affinity for ferric iron and are produced by bacteria under iron-limiting conditions (Matthew, Jenul, Carlier, & Eberl, 2016; Neilands, 1995). In E. coli, enterobactin is synthesized by the concerted action of the gene products encoded by the entCEBA operon (Crosa & Walsh, 2002; Ma & Payne, 2012; Walsh, Liu, Rusnak, & Sakaitani, 1990) It is exported from the cytoplasm by the inner membrane transporter protein EntS (Bleuel et al, 2005; Furrer, Sanders, Hook-Barnard, & McIntosh, 2002; Miethke & Marahiel, 2007). In P. aeruginosa, nickel has been shown to repress PCH synthesis (Visca et al, 1992) but induce PVD synthesis (Braud, Hannauer, Mislin, & Schalk, 2009) under iron-limited conditions. Our goal in this work is to test if nickel stress alters siderophore production under iron-limiting conditions in E. coli
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