Extraction and characterization of extracellular polymeric substances from a mixed fungal culture during the adaptation process with waste printed circuit boards

Abstract

Extracellular polymeric substances (EPSs) extracted from fungal mycelium by four chemical methods (NaOH, H₂SO₄, formaldehyde-NaOH, glutaraldehyde-NaOH), three physical methods (heating, ultrasound, vibration), and a control method (centrifugation alone) were investigated. Results indicated formaldehyde-NaOH outperformed other methods with 186.6 ± 8.0 mg/g of polysaccharides and 23.2 ± 4.6 mg/g of protein extracted and ensured little contamination by intracellular substances. Thereafter, this method was applied in extracting EPS from a mixed fungal culture in the adaptation process with 0.5% (w/v) waste printed circuit boards (PCBs). With the four adaptation stages continuing, the culture tended to become more sensitive to respond to the external toxic environment characterized by secreting EPS more easily and quickly. The maximum amount of polysaccharides and protein could be achieved in only 3 days both at the 3rd and 4th adaptation stage. Three-dimensional excitation-emission matrix fluorescence spectrum indicated the peaks obtained for EPS were mainly associated to soluble microbial by-product-like and aromatic protein-like compounds. Transmission electron microscopic observation illustrated that although metal ions penetrated into hypha cells, parts of them could be absorbed by EPS, implying that EPS secretion may be a primary protective strategy adopted by the culture.

Keywords: Adaptation; Extracellular polymeric substances; Extraction method; Mixed fungal culture; Three-dimensional fluorescence spectrum; Transmission electron microscopy; Waste printed circuit boards.