Acquisition of exogenous fatty acids renders apicoplast-based biosynthesis dispensable in tachyzoites of .

is a common protozoan parasite that infects a wide range of hosts, including livestock and humans. Previous studies have suggested that the type 2 fatty acid synthesis (FAS2) pathway, located in the apicoplast (a nonphotosynthetic plastid relict), is crucial for the parasite's survival. Here we examined the physiological relevance of fatty acid synthesis in by focusing on the pyruvate dehydrogenase complex and malonyl-CoA-[acyl carrier protein] transacylase (FabD), which are located in the apicoplast to drive fatty acid biosynthesis. Our results disclosed unexpected metabolic resilience of tachyzoites, revealing that they can tolerate CRISPR/Cas9-assisted genetic deletions of three pyruvate dehydrogenase subunits or FabD. All mutants were fully viable in prolonged cultures, albeit with impaired growth and concurrent loss of the apicoplast. Even more surprisingly, these mutants displayed normal virulence in mice, suggesting an expendable role of the FAS2 pathway Metabolic labeling of the Δα mutant showed reduced incorporation of glucose-derived carbon into fatty acids with medium chain lengths (C14:0 and C16:0), revealing that FAS2 activity was indeed compromised. Moreover, supplementation of exogenous C14:0 or C16:0 significantly reversed the growth defect in the Δα mutant, indicating salvage of these fatty acids. Together, these results demonstrate that the FAS2 pathway is dispensable during the lytic cycle of because of its remarkable flexibility in acquiring fatty acids. Our findings question the long-held assumption that targeting this pathway has significant therapeutic potential for managing infections.