Carboxylation of pyruvate with CO2 into the reverse tricarboxylic acid cycle promoted by water microdroplets

Pyruvate, serving as a bridge between the linear acetyl coenzyme A (acetyl-CoA) and the reductive tricarboxylic acid (rTCA) cycle, is of prime importance for life evolution. However, the carboxylation of pyruvate with carbon dioxide (CO 2 ) followed by coupling into the rTCA cycle remains challenging in prebiotic chemistry. Here, we present that pyruvate spontaneously undergoes carboxylation with CO 2, giving oxaloacetate, malate, and fumarate of the rTCA cycle in water microdroplets at room temperature without catalysts. The current pathway that pyruvate directly uses CO 2 as a carbon source depends on the microdroplet surface, distinct from the previously reported pathway using glyoxylate. These findings suggested that pyruvate may have participated in the cycle of enzyme-free carbon fixation on a prebiotic Earth. Furthermore, the widespread microdroplets in the atmosphere may also have acted as a potential synthesis setting for CO 2 fixation and utilization. This offers a promising strategy for climate change control and the promotion of sustainable carbon cycling in the future.