Physiological, Morphological, and Enzymatic Responses of Trametes versicolor to Lead Stress

초록

Lead (Pb) contamination may limit the use of white-rot fungi for lignocellulose waste conversion; however, fungal growth, morphology, and extracellular enzyme systems may exhibit different responses to Pb stress. In this study, after culturing the Trametes versicolor KACC 44767 strain for 30 d, the physiological, structural, and enzymatic responses to nominal Pb concentrations of 0, 100, 200, and 300 mg/L were evaluated. Mycelial dry weight, color, and microstructure, as well as lignin peroxidase (LiP), manganese peroxidase (MnP), β-glucosidase, and hemicellulase activities were analyzed. In addition, patterns according to treatment levels were analyzed using z-score heatmaps, hierarchical clustering, and exploratory Spearman correlation analysis. Dry weight decreased significantly from 216.1 ± 0.7 mg in the control group to 111.5 ± 1.1 mg after treatment with 300 mg/L Pb, representing a 48.4% decrease (Tukey’s honestly significant difference test, p < 0.05). The mycelial color changed from ivory to dark yellow. After treatment with 300 mg/L, the mycelial area ratio, branching, crossing, length, and aggregation increased, whereas porosity and pore size decreased compared to those of the control group. The enzymatic reactions were heterogeneous. LiP was maintained at up to 200 mg/L treatment and decreased at 300 mg/L, MnP peaked at 100 mg/L, hemicellulase peaked at 200 mg/L, and β-glucosidase decreased monotonically by 85.0% compared to the control group at 300 mg/L. Hierarchical clustering analysis revealed that the 100 and 200 mg/L treatment groups were the most closely grouped, whereas the 300 mg/L treatment group was isolated. Spearman correlation analysis showed inverse trends between Pb/color and dry weight/β-glucosidase depending on the treatment level. Overall, T. versicolor may retain the extracellular enzymatic potential associated with lignocellulose degradation under low-to-moderate Pb exposure, as indicated by the relative maintenance or induction of LiP, MnP, and hemicellulase activities. However, fungal growth and several types of enzyme activities were inhibited after high Pb exposure. Because substrate mass loss and compositional changes in lignin, cellulose, and hemicellulose were not assessed, these results should not be interpreted as direct evidence of lignocellulose degradation.

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