O 2 availability impacts iron homeostasis in Escherichia coli

Significance Our understanding of how cells regulate intracellular iron pools has been largely shaped by studying cells grown under aerobic conditions, in which the barrier to iron acquisition is dominated by O 2 -dependent insolubility. However, less is known about how bacteria meet their iron demands in the O 2 -limiting or anaerobic environments that are common to many ecosystems and reflective of the ancient atmosphere of early Earth. Because the transcription factor ferric-uptake regulator (Fur) plays a central role in controlling iron homeostasis in many bacterial species, we use Fur activity as a surrogate for understanding how anaerobiosis alters iron homeostasis. Our finding that levels of active Fur are increased during anaerobiosis emphasizes fundamental differences in bacterial iron requirements between aerobic and anaerobic growth conditions.