Sticky or thrifty: Divergence in extracellular glycometabolic architecture underpins contrasting fungal bioflocculation strategies

Abstract

Fungal-assisted bioflocculation is attracting attention as a chemical-free route for algal bloom mitigation and pollutants sequestration, but its species-specific traits that govern performance remain poorly quantified, hindering rational strain selection and scale-up. Here, we systematically compared three phylogenetically distinct fungi Aspergillus oryzae, Aspergillus niger and Pleurotus ostreatus interacting with the model cyanobacterium Synechocystis sp. PCC 6803 under bench-scale conditions relevant to drinking-water treatment. Despite producing the highest extracellular polymeric substances (EPS, 213.6 mg/g), Pleurotus ostreatus (Basidiomycota) achieved a 23 % lower harvesting efficiency than Aspergillus oryzae (150.1 mg/g). Quantitative EPS profiling revealed that mannose/galactose-rich glycoproteins in Aspergillus oryzae and ribose-enriched matrices in Aspergillus niger promoted microalgal adhesion, whereas the glucose-dense, storage-oriented EPS of Pleurotus ostreatus limited interfacial activity. Calcium addition further enhanced Aspergillus oryzae removal but impeded Pleurotus ostreatus, indicating clade-specific Ca²⁺-protein bridging mechanisms. Phylogenomic analysis traced these functional divergences to glycometabolic adaptations predating the Ascomycota–Basidiomycota split. We propose a layer-resolved EPS model: Ascomycota evolved surface-active glycan architectures for immediate cell capture, whereas Basidiomycota relies on protein networks that function primarily after surface disruption. This evolutionary-functional framework delivers quantifiable selection criteria, EPS sugar signature, Ca²⁺/protease responsiveness and peripheral thickness, that enable rational fungal selection for scalable and sustainable bioflocculants suitable for modern water-treatment applications.