The role of secondary metabolites in the production of CuO nanoparticles by fungi: a physiological and metabolic approach

Abstract

Previous studies showed that the biosynthesis of nanoparticles by diverse fungi is linked to the secretion of NADPH/NADH in the growth media. The results of these studies suggested that the mechanism of synthesis of nanoparticles is a generic pathway used by diverse fungi to synthesize different nanoparticles. However, very few studies have performed a systematic investigation to understand the conditions triggering the secretion of these essential biomolecules for the synthesis of nanoparticles or the chain of reactions leading to the production of biosynthetic nanoparticles by fungi. In the present study, we isolated the fungus Penicillium pimiteouiense from a copper mine in Brazil. Species of this genus have been previously described to synthesize different nanoparticles. In the present study, we determined that this fungus can secrete metabolites for the rapid (within 10 min) biosynthesis of copper oxide nanoparticles (CuO NPs) with a size range between 50 and 60 nm. The production of these secondary metabolites is mainly affected by temperature, pH, type of growth medium, and growth phase, but not by the presence of Cu²⁺. Metabolomics was used to further elucidate the chain of reactions in the synthesis of CuO NPs. According to the results, NADPH (nicotinamide adenine dinucleotide phosphate) dependent reductases (with NADPH as a cofactor), and secondary metabolites with phenolic groups were involved in the pathway as bio-reductants converting Cu²⁺ to CuO. The CuO NPs were further stabilized with peptides and other biomolecules, which served as capping agents leading to the thermodynamic stability of CuO NPs with a defined shape and size. This study confirms the previously reported role of NADPH/NADH in the synthesis of nanoparticles but brings additional information concerning other important biomolecules from fungal metabolites that also play a role in the biosynthesis of nanoparticles. Furthermore, this study identifies important physiological growth conditions that can affect the production of such metabolites. This work provides deeper mechanistic insights and potential commercial opportunities for recycling metal-rich mine wastes and green fabrication of nanoparticles.