Bacterial Biomolecules Drive Extracellular DNA Adsorption onto Ferrihydrite: Interfacial Interactions and Spectroscopic Insights

The reactivity of extracellular DNA (exDNA) at the mineral interface, modulated by interactions with other biomolecules, may play an important role in governing the fate of genetic information in the environment. However, there is a limited understanding of exDNA-mineral interactions with biomolecule-enriched matrices. Herein, we investigate the mechanisms of exDNA adsorption onto ferrihydrite in the presence of bacterial lysate biomass. The interactions within the system were explored by combining exDNA adsorption studies, zeta potential measurments, spectroscopic studies, and advanced spectrochemical imaging by scattering-type Scanning Near-Field Optical Microscopy (s-SNOM). Bacterial lysate biomass is found to enhance the immobilization efficiency of exDNA by the ferrihydrite. A key role in this process is played by proteins bearing positively charged groups, which facilitate interactions and co-adsorb with exDNA. When the bacterial biomass concentration reaches 14.03 μg/mL, the exDNA removal efficiency nearly doubles relative to the system with sole ferrihydrite. The effect of biomolecules in promoting exDNA adsorption onto ferrihydrite is further demonstrated by s-SNOM. The spectral bands of biomolecules tend to overlap and co-occur in specific regions of conjugates as biomass concentration increases. Our results provide important mechanistic insight into the process potentially influencing the fate of exDNA in environments such as biofilms, soils, and sediments.