Interaction between mercuric chloride and extracellular polymers of biofilm-forming mercury resistant marine bacterium Bacillus thuringiensis PW-05

Abstract

The interaction mechanism of mercury (Hg²⁺) with extracellular polymers (EPS) produced from a mercury resistant marine bacterium Bacillus thuringiensis PW-05 was studied. Extracted EPS contained 1546.93 ± 53.63 μg ml⁻¹ of carbohydrate, 156.70 ± 6.77 μg ml⁻¹ of protein and 3.78 ± 0.29 μg ml⁻¹ of DNA. The zeta potential was increased from −9.08 ± 0.12 mV of pristine EPS to −1.39 ± 0.07 mV of mercury interacted EPS. >90% of Hg²⁺ was absorbed by the EPS from the solution after 2 h. UV-Vis, FTIR and ¹H NMR spectroscopy revealed the possible role of carboxyl, phosphoryl, hydroxyl, amino and sulfhydryl functional groups in the interaction process. EPS architecture was found to be modified from purely amorphous to fairly crystalline after interaction with mercury as revealed by XRD. The interaction process was found to be spontaneous with negative free energy (−61.77, −63.17 and −61.74 J mol⁻¹ at 298, 308 and 318 K respectively) and an enthalpy driven process.