Fungal biosynthesis of gold nanoparticles with sporicidal activity against bacterial endospores

Gold nanoparticles (AuNPs) have a wide range of applications due to their optoelectronic properties. Particularly, biological synthesis of AuNPs highlights due to the advantages related to the environmental care and the stabilization provided by capping biomolecules during biosynthesis. The antimicrobial activity of AuNPs was reported, however, their activity against resistant structures such as bacterial endospores have not been evaluated. This work shows the extracellular biosynthesis of AuNPs using Epicoccum nigrum (Au1-8) throughout an ecofriendly, simple, and efficient method. Physicochemical characterization revealed that stable quasi-spherical AuNPs in a range size of 2 to 30 nm, with crystal structure and metallic Au0 composition were obtained. The AuNPs sporicidal activity against Bacillus subtilis endospores was evaluated by its exposure to 300 mg/L AuNPs during 48 h, which produced a decrease of 90.6% of the endospore germination. The analysis of the endospore-AuNP interaction by scanning electron microscopy (SEM) and infrared (IR) spectroscopy revealed injury of the endospore coat and lysis. These results are promising for the advance in the development of low-aggressive agents used for environmental decontamination regimens against pathogenic bacterial spores, or even as an alternative for the treatment of illnesses produced by endospore-former causative agents of food spoilage/poisoning and human diseases.