Zinc oxide nanoparticles hinder fungal biofilm development in an ancient Egyptian tomb

Nanoparticles (NPs) have been proposed as an innovative strategy to prevent fungal colonization of cultural heritage, but until now their efficacy has mainly been proved against fungi in planktonic conditions. Four fungi from microbial alterations of the royal tomb of Tausert and Setnakht in the Valley of the Kings, Thebes, West Bank, Modern Luxor, Egypt, were isolated and identified as Alternaria alternata, Aspergillus niger, Penicillium chrysogenum and P. pinophilum. This work deals with four developing fungal biofilms grown with a colony biofilm approach, and exposed to two concentrations of zinc oxide NPs (0.25 and 0.5%) for 10 days. A significant reduction in the biofilm growth was observed in presence of 0.5% NPs for all fungi, except A. niger. Moreover, the morphology of the fungal biofilm exposed to NPs differed from that of the control, and there was a different polysaccharide to protein ratio in the matrices, and earlier production of coloured compounds and spores. Despite the success of the zinc oxide NPs, this early metabolite production needs to be monitored as a possible source of substances affecting cultural heritage surfaces.