Glomalin-related soil protein: The particle aggregation mechanism and its insight into coastal environment improvement

Glomalin-related soil protein (GRSP), a ubiquitous microbial product, plays a crucial role in particle aggregation and metal adsorption, but the underlying mechanisms remain unknown. Here, GRSP fraction was extracted from estuarine ecosystems and systematically characterized to elucidate the aggregation mechanisms and its impact on coastal environment improvement. We found that GRSP fraction (gravimetric mass of extracted GRSP, 5.1-24.3 mg g-1) was a globally relevant novel bioflocculant and that protein (linked to Bradford protein assay, 1.64-4.37 mg g-1) was the active flocculant constituent. The zeta potential, FTIR, XPS, and 13C NMR analyses identified its key constituents and structure, and revealed that the charge neutralization and bridging were GRSP fraction aggregation mechanisms. Thermogravimetric-infrared spectrometry analysis showed that GRSP fraction was highly thermostable, and the main volatile pyrolysis products included H2O, CO2, CO, and CH4. The SEM-EDX and XPS Fe valence spectroscopy suggested that GRSP fraction contained rich Fe (11.91 ± 0.48%) and could form Fe-rich flocs with particles. We also found that GRSP fraction has a high adsorption capacity (76-95%) for Cu, Zn, Pb and Cd, and its flocculation properties provide new insights into metal adsorption. The analysis of particle aggregation mechanism and its metal adsorption capacity is of great significance to elucidate the role of GRSP fraction in coastal environment improvement.