Extracellular Matrix of Biofilm Regulates the Stress Tolerance Mechanism in Aspergillus terreus HLP5 Against Lead and...

Lead [Pb(II)] and phenanthrene are major environmental co-pollutants that pose a serious threat to all life forms. The present study highlights the biofilm-associated stress responses in the marine filamentous fungus Aspergillus terreus HLP5 to various concentrations of Pb(II) and phenanthrene (25-500 ppm, 1:1 ratio). Highest biofilm formation shifted from 48 h in control to 72 h in presence of co-pollutants. A reduced surface-to-volume ratio in biofilm formed at 25-50 ppm Pb(II) + Phe indicated increased mycelial aggregation and compact architecture. The hyphal diameter increased with co-pollutant concentration. Gene expression analysis revealed downregulation of ags gene, whereas somA, medA, uge5, uge3, and gtb3 expression peaked at 72-96 h in 25-100 ppm of Pb(II) + Phe. Extracellular matrix (ECM) exhibited compositional and conformational modifications in polysaccharide and protein content. Major shifts were observed in functional groups corresponding to hydroxyl, Amide I-II, carboxyl, and phosphate moieties. Distinct peak at 8.36 ppm in ¹H NMR revealed phenanthrene-ECM interaction. A decrease in fluorescence intensity of tryptophan-like residues (290/355 nm) indicated ECM-co-pollutant binding. Upregulation of stress response genes (gst, acot2) and antioxidants like glutathione S-transferase, superoxide dismutase, and proline contributed to reduced ROS accumulation and redox homeostasis. These findings illustrated enhanced stress resilience of ECM-covered biofilm under co-pollutant stress.