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Evaluating the Role of PET in Fungal Cellulase Induction: Chemical Signal or Physical Growth Substrate?
Summary
Researchers tested whether PET fibres chemically induce cellulase production in Aspergillus niger and Trichoderma reesei, finding that enzyme secretion is driven entirely by cellulose availability and physical surface area rather than any biochemical signal from PET — establishing PET as a structural scaffold that can support but not trigger fungal enzyme production in blended textile waste.
The rapid expansion of synthetic textile production, particularly polyethylene terephthalate (PET) fibres, has intensified concerns over microplastic generation and the management of mixed-fibre textile waste. Fungal cellulases offer a low-impact route for biological upcycling of such materials; however, it remains unclear whether PET actively induces cellulase production or functions only as a physical support. This study explicitly tests the hypothesis that PET contributes to cellulase secretion through physical rather than biochemical mechanisms . Cellulase production by Aspergillus niger and Trichoderma reesei was evaluated using textile-derived substrates (100% cotton, 100% PET, and cotton–PET blends) and inert materials (glass, ceramic beads, sponge, and plastic flakes) under submerged (SmF) and solid-state fermentation (SSF). The highest enzyme titres were obtained on cotton-rich blends, with a 60% cotton/40% PET fabric yielding 0.546 ± 0.04 U mL⁻¹ by A. niger after 3 days, directly supporting the hypothesis that cellulase induction is governed by cellulose availability rather than PET chemistry. Pure PET did not stimulate cellulase synthesis, whereas PET-containing blends and inert supports enabled measurable enzyme release. Across non-cellulosic substrates, cellulase output increased systematically with available surface area (4–10 mm), reaching 0.415 ± 0.04 U mL⁻¹ on 10 mm ceramic beads, providing direct evidence that enzyme secretion under non-inducing conditions is driven by physical attachment rather than chemical signalling. By decoupling biochemical induction from surface-mediated effects, this work establishes PET as a structural scaffold rather than a biochemical inducer and highlights the scalability of surface-engineered, low-energy fungal fermentation strategies for valorising realistic blended textile waste streams. • PET acts only as a physical scaffold that supports fungal attachment. • Surface roughness and contact area control cellulase secretion on inert supports. • Ceramic beads and high‑area substrates boost cellulase output via better adhesion. • Polycotton blends induce strong cellulase via cellulose cues and PET anchoring.