FIT plays a role in iron acquisition in Toxoplasma gondii

The obligate intracellular apicomplexan parasite Toxoplasma gondii requires iron as a cofactor for essential metabolic proteins. Due to its importance to almost all life, iron uptake and regulation have been well studied across model eukaryotes. Iron acquisition has been studied in some detail in parasitic kinetoplastids like Leishmania. However, despite its importance, little is known about how Toxoplasma gondii acquires iron. Many organisms make use of specific transporters, named Zinc and Iron Permeases (ZIPs) to take up iron from their environments. T. gondii encodes four ZIP-domain containing proteins, one of which, named here as FIT, is predicted to localize to the plasma membrane and is essential for parasite growth. We endogenously tagged FIT with 3HA tags and show that its localization is dynamic, localizing initially peripherally, before moving basal during parasite replication. Overexpression of FIT provides a protective effect when iron is depleted, but cells are hypersensitive to excess iron, when compared to wildtype parasites. Interestingly, ICP-MS experiments show that FIT overexpression leads to Zn accumulation in the parasite, however no change was seen in parasite associated iron. To determine function, we conditionally depleted of FIT, which led to a severe growth defect in vitro, suggesting it is essential for parasite survival. X-ray fluorescence microscopy (XFM) data show that FIT knockdown leads to reduced parasite iron. Moreover, ICP-MS data show that knockdown of FIT results in a decrease in Zn in the parasites. Finally, we show that knocking down FIT leads to an increased expression of bradyzoite markers including BAG1 and DBL, suggesting that knockdown of FIT may lead to the conversion/differentiation of tachyzoite parasites to the cyst-forming bradyzoite form of the parasite. Interestingly, depletion of iron by chelation also promotes differentiation, suggesting a similar mechanism and a role for iron in triggering differentiation. Together, we show that FIT has a role in iron uptake, and possibly zinc uptake in Toxoplasma gondii, and that this is important for parasite survival in vitro.