Evaluating the Role of PET in Fungal Cellulase Induction: Chemical Signal or Physical Growth Substrate?

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.