Scaling EPS yield and bio-carrier application of Bacillus paralicheniformis UB08 for rapid lead remediation

Heavy metal pollution from industrial operations poses severe environmental risks due to its toxicity and bioaccumulation. Conventional chemical and physical remediation methods are costly and generate secondary toxic sludge. Therefore, this study aims to investigate the potential of extracellular polymeric substance (EPS) producing bacteria as a sustainable, eco-friendly alternative for bioremediation.

EPS producing bacteria were isolated from chemical factory effluent sludge and screened on modified Winogradsky's medium. The isolates were identified by 16S rRNA gene sequencing and phylogenetic analysis. Heavy metal tolerance to lead (Pb), cadmium (Cd), and mercury (Hg) was evaluated in tryptic soy broth (TSB) containing up to 9,000 ppm of each metal. Culture conditions, including carbon/nitrogen sources, pH, and temperature, were optimized to maximize biomass and EPS yield. Functional groups of EPS were characterized by Fourier transform infrared (FTIR) spectroscopy. To assess bioremediation efficiency, the bacterial isolate was immobilized and encapsulated on ceramic rings, water hyacinth stems, and alginate beads. The surface morphology of the bio-carriers was visualized using field-emission scanning electron microscopy (FESEM). Pb removal efficiency (15 ppm) was quantified using flame atomic absorption spectrophotometry (FAAS).

Among the isolated strains, the most potent strain, Bacillus paralicheniformis UB08 (TISTR 10842), displayed an extraordinary nominal Pb tolerance, with a minimum bactericidal concentration (MBC) exceeding 9,000 ppm. In contrast, the strain remained highly sensitive to Cd and Hg with MBC of seven ppm and four ppm, respectively. Optimization in modified TSB (MTSB), containing 0.6% sucrose and 4% yeast extract at pH 6.0 and 55 °C, enhanced EPS production 5.5-fold to 0.4524 ± 0.0176 g/100 ml compared with 0.0821 ± 0.0076 g/100 ml in standard TSB. EPS was characterized as a glycoprotein containing 35.92% glucose and 60.08% fructose equivalents (quantified relative to their respective standards) and 1.35% protein, with a polysaccharide backbone enriched with hydroxyl and amine functional groups. FESEM imaging verified successful biofilm formation and cell immobilization on all matrices. In bioremediation tests, free cells achieved 33.9% of Pb removal. Notably, alginate bead-encapsulated UB08 achieved 100% Pb removal within 2 days, significantly better than immobilization on water hyacinth (100% at 5 days) and ceramic rings (71.51% at 7 days).

B. paralicheniformis UB08 demonstrates exceptional thermotolerance and highly efficient Pb removal from solution. Alginate bead encapsulation enables rapid and complete Pb removal, offering a promising solution for heavy metal treatment based on physical adsorption and potential biological synergies.