Long-term Evaluation of Culturable Fungi in a Natural Aging Biofilm on Galvanized Steel Surface

Fungi commonly found in municipal water can participate in the natural biofilm formation on the surfaces of galvanized steel despite the toxic effect of Zn, and also depending on the age of the biofilm, fungal diversity may vary. To examine this hypothesis, natural biofilm formation was allowed on galvanized steel surfaces over 6 months in a model recirculating water system. Fungal colonies with different morphologies were obtained monthly from biofilm and water samples and then identified by both morphological and molecular approaches. In addition, the biofilm layer was examined by electrochemistry impedance spectroscopy (EIS) analyses and scanning electron microscopy. It was determined that the fungi were included in the natural aging biofilm formed on the galvanized steel surfaces over the experiment. The diversity and the number of fungi in the biofilm and water changed over the experiment. All of the fungi isolated from the biofilm and water were found to be members of the Ascomycota phylum. F. oxysporum was the first fungus to be involved in the biofilm formation process and also it is one of the main inhabitants of the biofilm together with Penicillium spp. In addition, EIS data showed that the structure of the biofilm changed as it ages. The results of this study may lead to a better understanding of natural aging biofilms involving fungi in municipal water systems, as well as the development of new strategies for effective disinfection of fungi based on biofilm age.