Iron Efflux as a Mechanism of Iron Overload Resistance in Bacillus subtilis
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Pinochet Barros, Valentina Azul
Iron is an essential element across all domains of life. However, when in excess, this micronutrient is toxic as it can target metalloproteins for mismetallation, and undergo Fenton reactions that generate damaging reactive oxygen species (ROS). Bacteria have developed ways to balance intracellular iron levels and regulate oxidative stress responses. In the model Gram-Positive, non-pathogenic bacterium Bacillus subtilis, iron homeostasis and the oxidative stress response is tightly regulated by the Fur family metalloregulators Fur and PerR respectively. Under oxidative stress, PerR derepresses a regulon comprised of peroxide detoxifying enzymes and proteins that lower labile iron pools. During periods of iron starvation, Fur derepresses expression of iron importers, allowing the cells to acquire more iron. On the other hand, under high iron levels, iron export has not been reported until recently. In this work we have expanded our understanding of this newly emerging field through the discovery of the first member of the P1B-family of ATPase transporters to be involved in ferrous iron efflux, PfeT. This B. subtilis Fe2+ efflux pump is part of the P1B4-class of ATPases, which in the past has been attributed to cobalt export. This doctoral thesis centers on the identification and characterization of PfeT as an Fe2+ exporter which is essential to the cell under iron overload conditions (Chapter 3). From this, we go on to elucidate the complex transcriptional regulation of the pfeT gene. Not only do we show direct transcriptional activation by Fur for the first time in Gram-positives, but expand this model to the Listeria monocytogenes Fe2+ efflux ortholog, frvA (Chapter 4). Finally, the recent discovery of cation diffusion facilitator (CDF) Mn2+ exporters MneP and MneS provides further insight into Fe2+ efflux (Chapter 5). We redefine these transporters as Mn2+/Fe2+ efflux pumps, highlighting metal cross-talk in B. subtilis and its impact on oxidative stress.
Peters, Joseph; Nicholson, Linda
Ph. D., Microbiology
Doctor of Philosophy
dissertation or thesis