Arsenic Adsorption and Toxicity Reduction of An Exopolysaccharide Produced by Bacillus licheniformis B3-15 of Shallow Hydrothermal Vent Origin

Exopolysaccharide (EPS) production represents an adaptive strategy developed by extremophiles to cope with environmental stresses. The EPS-producing Bacillus licheniformis B3-15, of shallow marine vent origin (Vulcano Island, Italy), was previously reported as tolerant to arsenate (As-V). In this study, we evaluated: (i) the increasing production of EPS by Bacillus licheniformis B3-15 in the novel SG17 medium; (ii) the arsenic absorption capacity of the EPS by mass spectroscopy; (iii) the functional groups of EPS interacting with As by ATR-FTIR spectroscopy; and (iv) the ability of EPS to prevent arsenic toxicity by the bioluminescent assay. The EPS yield (240 mg L-1) was 45% higher than previously reported. The EPS was mainly constituted of disaccharide repeating units with a manno-pyranosidic configuration and low protein content, attributed to the poly-gamma glutamic acid component as evidenced by NMR analysis. ATR-FTIR spectra indicated that the functional groups of the EPS (O-H, C=O, C-O and C=C and N-O) were involved in the adsorption of the arsenic cations, with greater interactions between EPS and arsenate (As-V) than arsenite (As-III). Consequently, the EPS at increasing concentration (100 and 300 mu g mL(-1)) adsorbed As-V more efficiently (20.5% and 34.5%) than As-III (0.7% and 1.8%). The bioluminescence assay showed that the EPS was not toxic, and its addition reduced the toxicity of both As forms by more than twofold. The crude EPS B3-15 could be used in arsenic bioremediation as a possible eco-friendly alternative to other physical or chemical methods.