A novel bioflocculant competent of coagulating and flocculating the polystyrene from an Alcaligenes sp.

Microplastics (MPs) in environmental matrices, particularly aquatic ecosystems, pose an emerging threat to diverse biological systems. Coagulation-flocculation processes have garnered attention for their potential to mitigate MP contamination in wastewater treatments and may help to limit these particles ending in water bodies. This study explores a sustainable way to precipitate PS nanoparticles (PS NPs), utilising a protein bioflocculant from Alcaligenes sp. IS02 as an alternative to chemical and synthetic flocculants. The cell-free culture supernatant demonstrated a substantial turbidity clearance of 85% in prepared PS suspension, signifying its efficacy in removing the PS-NPs. The protein bioflocculant was precipitated and extracted with 10% trichloroacetic acid, and the purified flocculant displayed a flocculation activity (FA) of 84.1%. The role of proteins in flocculation was confirmed by desorbing the multiple proteins from the precipitated PS NPs and separated through SDS-PAGE and also validated the presence of proteins by FTIR. It was also observed that the suspension’s zeta potential increased from − 49.16 mV to − 31.9 mV after the addition of the bioflocculant, indicating the role of charged residues in flocculation. The possible mechanism for flocculation was presumed as protein corona formation, where electrostatic interactions between negatively charged PS NPs and charged amino acid residues in proteins lead to aggregation and precipitation.