Extracellular Toxoplasma gondii tachyzoites do not require carbon source uptake for ATP maintenance, gliding motility and invasion in the first hour of their extracellular life.

Apicomplexan parasites undergo metabolic shifts in adaptation to environmental changes. Here, we investigate the metabolic requirements which are responsible for ATP homeostasis in the extracellular stage of Toxoplasma gondii. Surprisingly, we found that freshly released tachyzoites are able to maintain a constant ATP level during the first hour of extracellular incubation without the acquisition of external carbon sources. We further demonstrated that the extent of gliding motility and that of host cell invasion is independent from the availability of external carbon sources during this one hour extracellular period. The ATP level and the invasion efficiency of extracellular parasites were severely decreased by treatment with the glycolysis inhibitor, 2-deoxy-d-glucose, but not by the F(0)F(1)-ATPase inhibitor, oligomycin. This suggests that although the uptake of glucose itself is not required during the 1h incubation period, extracellular parasites depend on the activity of the glycolytic pathway for ATP homeostasis. Furthermore, active glycolysis was evident by the secretion of lactate into the culture medium, even in the absence of external carbon sources. Together, our studies suggest that tachyzoites are independent from external carbon sources within the first hour of their extracellular life, which is the most relevant time span for finding a new host cell, but rely on the glycolytic metabolisation of internal carbon sources for ATP maintenance, gliding motility and host cell invasion.