Treatments that eradicate tachyzoites and bradyzoites Toxoplasma gondii (T. gondii) remain non-existent and essential and druggable processes in bradyzoites remain hard to identify. Using a new in vitro model for pan-drug tolerant bradyzoites¹, we found Argyrin D (ArgD) among 253 myxobacterial compounds to inhibit tachyzoite growth while also acting on bradyzoites at half maximal concentrations of 3 and 60 nM, respectively. In other eukaryotes and bacterial pathogens argyrin compounds have been shown to disrupt translation by binding to the elongation factor G (EFG).² T. gondii harbors three isoforms of EFG that are expressed in its cytosol, apicoplast and mitochondrion. Surprisingly, fluorescent streptavidin staining of treated tachyzoites demonstrates absence of a delayed death phenotype. Instead, parasites that express GFP in their mitochondria revealed a defect in the mitochondrial morphology. We used a SILAC approach to monitor the change of global protein synthesis in ArgD-treated parasites by incorporation of stable-isotope labelled amino acids. In total the synthesis of 119 proteins was significantly attenuated over the course of three days. After 24 hours of treatment we identified 41 proteins that were enriched in mitochondrial proteins and included the mitochondrially encoded cytochrome b and cytochrome c oxidase III. After 48 and 72 h the synthesis of proteins from all cellular compartments was impacted. In summary, we identified an inhibitor of mitochondrial translation that will be a useful tool to identify and study essential mitochondrial processes in both parasite stages.

1: Christiansen, C., Maus, D., Hoppenz, E. et al. In vitro maturation of Toxoplasma gondii bradyzoites in human myotubes and their metabolomic characterization. Nat Commun 13, 1168 (2022). https://doi.org/10.1038/s41467-022-28730-w

2: Nyfeler, Beat et al. "Identification of elongation factor G as the conserved cellular target of argyrin B." PloS one vol. 7,9 (2012): e42657. doi:10.1371/journal.pone.0042657