Exploring lead biosorption via Lactobacillus-based exopolysaccharides and biofilms: A structural and functional study

Toxic heavy metals such as lead (Pb) persistently accumulate in ecosystems as a result of unregulated anthropogenic activities, posing significant threats to both environmental and human health. The widespread occurrence of Pb contamination underscores the urgent need for efficient remediation strategies. This study aims to optimize the biosorption of lead [Pb(II)] using biofilms and exopolysaccharides (EPS) synthesized by Lactiplantibacillus plantarum , Limosilactobacillus reuteri , and Lactiplantibacillus sp. strain ANPSCRLB. The strains were examined for their minimum inhibitory concentration and Pb(II) biosorption efficiency across concentrations ranging from 100 to 350 mg/L. Among the tested strains, the biofilm of Lactiplantibacillus sp. ANPSCRLB demonstrated the highest lead biosorption capacity (2.95 ± 0.01 mg/L), followed by L. plantarum (2.89 ± 0.09 mg/L) and L. reuteri (2.61 ± 0.01 mg/L) at pH 4 and 37 °C. Biosorption increased progressively from 6 h to 24 h for both EPS and biofilm samples, reaching a maximum at 24 h, with Pb(II) removal efficiencies ranging from 81.6 % to 95.6 % for biofilms and 85.3–96.3 % for EPS matrices. FTIR analysis indicated shifts in EPS peaks from 3293 cm⁻¹ to 2923 cm⁻¹ after Pb(II) biosorption, suggesting the involvement of O–H, C–H, and N–H functional groups associated with proteins and polysaccharides in metal binding. SEM micrographs revealed that both EPS and biofilm exhibited heterogeneous, porous surface structures with large folds, while structural analysis confirmed dense cell clusters embedded within EPS, forming robust biofilm-like networks with numerous active binding sites. The study demonstrates the potential of LAB-derived biofilms and EPS as sustainable and efficient biosorbents for the removal of heavy metals from aqueous environments. • LAB biofilms and EPS have potential as biosorbents for lead (Pb) removal. • Maximum Pb(II) removal was achieved at pH 4 and 37°C after 24 h of incubation. • Microscopy shows EPS-embedded cell clusters forming stable, metal-binding biofilms. • LAB biofilms and EPS enable sustainable, efficient heavy metal remediation in water.