Captan-induced pyruvic acid fermentation by Rhizopus oryzae: Mechanistic insights from targeted metabolomics.

Pyruvic acid, a key intermediate in pharmaceutical and chemical industries, serves as a central metabolic hub connecting multiple intracellular pathways. Biological production of pyruvic acid offers environmental and sustainability benefits. However, pyruvic acid accumulation and secretion are often restricted by microbial metabolic regulation. In this study, the exogenous phthalimide inhibitor captan was applied to regulate pyruvic acid metabolism in Rhizopus oryzae, resulting in pyruvic acid accumulation of 1.15 g/L at 6 mg/L captan. The measured activities of pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) were significantly decreased. Under 10 mg/L captan, PDH and PC activities were decreased by 59% and 56%, respectively, thereby promoting pyruvic acid accumulation. Central carbon-targeted metabolomics identified 43 differentially expressed metabolites, with downregulation of the pyruvic acid metabolic node. Energy metabolism was shifted from the tricarboxylic acid (TCA) cycle to glycolysis. Captan treatment reduced the biomass accumulation of R. oryzae, while its cellular ultrastructure remained unaffected. These results elucidate the mechanism of captan-driven pyruvic acid fermentation, laying a foundation for sustainable waste-to-resource bioprocesses for pyruvic acid production.