Dual extracellular mycofabrication of cobalt and zinc nano metal oxides mediated by mycelial-cell free filtrate of Aspergillus sojae: Characterization and assessment of antibacterial activity

Abstract

Foodborne pathogenic bacteria cause a wide range of infectious diseases that pose a serious threat to human health worldwide with significant social and economic consequences. Nano metal oxides have attracted paramount attention owing to their remarkable antimicrobial potency. Microbial synthesis of metal oxide nanoparticles has gained prominence due to cost-effectiveness, biocompatibility, and environmental friendliness. This study reports extracellular mycosynthesis of two nano metal oxides mediated by Aspergillus sojae mycelial cell-free filtrate (MCFF). A. sojae MCFF was reacted with cobalt chloride hexahydrate and zinc nitrate hexahydrate for the preparation of Co3O4 NPs and ZnO NPs, respectively. After reacting with each metal salt, A. sojae MCFF changed from transparent to greyish-brown and white-milky suspensions, indicating the mycosynthesis of Co3O4 NPs and ZnO NPs, respectively. Physicochemical and morphological properties of the two nano metal oxides were determined using various characterization techniques, involving XRD, FTIR, EDX, DLS, zeta potential analysis, XPS, and electron microscopy. The two nano metal oxides exhibited antibacterial potency against three foodborne pathogens. Co3O4 NPs had zones of inhibition (ZOI) of 19.33 ± 0.58, 20.67 ± 0.58, and 22.67 ± 0.58 mm against Escherichia coli (ATCC 43889), Salmonella enterica Serovar Typhimurium (ATCC 43174), and Staphylococcus aureus (ATCC 12600), respectively. Whereas ZnO NPs had ZOI of 15.67 ± 0.58, 15.67 ± 0.58, and 14.33 ± 0.58 mm against the three foodborne pathogens, respectively. The intact morphological structures of the bacterial cells collapsed following exposure to A. sojae-mediated Co3O4 NPs and ZnO NPs, with some cells having irregular, twisted, and rough surfaces. The current study concluded that A. sojae mycelia acted as potential biological entity for the biosynthesis of Co3O4 NPs and ZnO NPs. A. sojae-derived Co3O4 NPs and ZnO NPs can be potential candidates for use as antimicrobial nano metal oxides in food and pharmaceutical industries.