Functional amyloid fibrils in the marine bacterium Pseudomonas aeruginosa PFL-P1 interact with lead and upregulate the fapC gene for heavy metal sequestration

Bacteria flourish within biofilms enveloped in an intricate three-dimensional network of extracellular polymeric substances (EPS). Functional amyloid in Pseudomonas (Fap), a fibrous protein within EPS, displays proficient heavy metal-binding capabilities. The present study delves into the interaction between Fap fibrils produced by Pseudomonas aeruginosa PFL-P1 and lead [Pb(II)], followed by investigating the molecular mechanisms and potential applications for heavy metal bioremediation. Thioflavin T based fluorescence microscopy revealed that Pb(II) exposure triggered an increase in Fap fibril secretion within the biofilm. Furthermore, the significant (p = 0.0025) upregulation of fapC gene in response to Pb(II) stress highlighted the role of amyloid structures as crucial components in bacterial defense, metal sequestration, and cellular protection. The microscopic and spectroscopic studies revealed fibrillar morphology, conformational changes, enhanced β-sheet content, and emergence of Pb(II)-associated crystalline regions in the purified Fap fibrils upon Pb(II) interaction. Fluorescence spectroscopy showed substantial quenching of a protein-like fluorophore in Fap fibrils upon Pb(II) exposure, with binding constants of 2.69–3.05 M−1, indicating the strong affinity and a single binding site (n = 1) for Pb(II) ions. Thermodynamic analyses suggested an exothermic and spontaneous interaction at 305 K. Exogenously added Fap fibrils efficiently removed 97.88 ± 1.86 % of Pb(II) in 24 h, with a maximum adsorption capacity (qm) of 30.49 mg/g and a higher Langmuir constant (KL) of 0.22 L/mg, indicating strong binding affinity. Langmuir isotherm modeling validated monolayer adsorption, following a pseudo-second-order reaction with chemisorption as the dominant mechanism. The findings highlighted the potential of Fap fibrils for heavy metal sequestration and provide insights into their molecular interactions.