Optimization and Characterization of Exopolysaccharide Production from Alkali-tolerant Alkalihalobacillus sp. using Response Surface Methodology for Cr (VI) Biosorption

Abstract

Bacterial exopolysaccharides (EPS) are highly versatile, finding applications across various fields due to their extensive functional properties. Notably, EPS is often produced by bacterial cells as a defense mechanism under stressed conditions like, high alkalinity and salinity. In the current research, Alkalihalobacillus sp. multi-stress tolerant bacteria isolated from Bauxite residue was investigated for EPS production, under alkaline conditions. Further, to enhance EPS yield, surface response methodology (Box-Behnken model) was employed. The optimized nutrient conditions for maximum EPS yield were 1.8 g/L of glucose, 9.54 g/L of nitrogen, 0.85 g/L of MgSO₄ and an incubation time of 5 days at 37 °C. These optimized conditions resulted in increase in EPS production, achieving a yield of 1.78 g/L. Characterization of the EPS, including FTIR and NMR, suggest association of different functional groups including hydroxyl, carbonyl, sulphate and phosphate. XRD study revealed the semicrystalline nature of EPS and Fe-SEM highlighted its porous structure. Zeta potential analysis highlighted the EPS's anionic characteristics. Furthermore, the study explored the EPS's capability for chromium adsorption, demonstrating a capacity of 63–68 mg/g. The adsorption efficiency was highest within a pH range of 3–6, with the Langmuir model providing the best fit for the adsorption isotherm. In conclusion, EPS production from Alkalihalobacillus sp., showed significant increase of 3.6-fold with optimized conditions and exhibits potential as a biosorbent for chromium removal from industrial wastewater, warranting further investigation.