Evaluation of Metal Tolerance of Fungal Strains Isolated from Contaminated Mining Soil of Nanjing, China

Abstract

Rapidly increasing industry has resulted in greater discharge of hazardous chemicals in the soil. In the current study, soil samples were collected from Nanjing mine (32°09'19.29″ N 118°56'57.04″ E) and subjected to heavy metal analysis and microbe isolation. A total of 460 fungi were isolated, and five of these were yeast strains. Most of the strains exhibited tolerance to one metal. Five multimetal tolerant strains were selected and identified as <i>Aspergillus sclerotiorum</i>, <i>Aspergillus aculeatus</i>, <i>Komagataella phaffii</i>, <i>Trichoderma harzianum,</i> and <i>Aspergillus niger</i>. Isolated strains were grown in high concentrations of cadmium (Cd), chromium (Cr) and lead (Pb), for induced-tolerance training. The tolerance index (TI) revealed the highest Cd tolerance of novel <i>K. phaffii</i> strain at 5500 ppm (TI: 0.2). <i>K. phaffii</i> also displayed resistance at 4000 ppm against Cr (TI: 0.32) and Pb (TI: 0.32). In contrast, tolerance training for <i>A. niger</i> was not that successful. <i>K. phaffii</i> also displayed the highest bioaccumulation capacity for Cd (25.23 mg/g), Cu (21.63 mg/g), and Pb (20.63 mg/g) at 200 ppm. Scanning electron microscopy (SEM) explored the morphological changes in the mycelia of stressed fungi. Results of this study describe this delicate approach to be species and metal dependent and suggest a potential utilization of this fungal strain for the bioremediation of contaminated soils.