Toxoplasma survives the loss of key enzymes of peroxide and glutathione metabolism

Toxoplasma gondii is an obligate intracellular protozoan parasite that replicates rapidly in a variety of host cells. The parasite encodes diverse enzymes of glutathione and peroxide metabolism, but their physiological roles remain poorly understood. Herein, we shed a new perspective on the functions and relevance of the peroxiredoxin and glutathione metabolism in the zoonotic pathogen T. gondii. We show that two cytosolic peroxidases (TgPRX1, TgPRX2), a mitochondrial peroxiredoxin (TgPRX3), and the cytosolic glutathione reductase (TgGR2), glutamate-cysteine ligase (TgGCL), and glutathione synthetase (TgGS) are not required for the lytic cycle of T. gondii under standard growth conditions. However, mutants lacking the gene for either TgPRX1 or TgGR2 exhibited increased susceptibility to exogenous hydrogen peroxide compared to wild-type parasites. Furthermore, we found that the combined deletion of TgPRX1 and TgPRX2 led to a notable impairment of parasite growth, suggesting a functional redundancy between the two peroxidases. Finally, our results show that the apicoplast glutathione reductase (TgGR1) is required for normal parasite growth in vitro and in vivo but is not essential for parasite survival. Our findings highlight that the redox metabolism of Toxoplasma is surprisingly robust and flexible, allowing the parasite to survive under the loss of several key enzymes of peroxide and glutathione metabolism.