Potentialities of the exopolysaccharide produced by the thermophilic Bacillus licheniformis B3-15 in the remediation of arsenic-polluted aquatic environments

Hydrothermal vents of Eolian Islands are extreme environments characterized by prohibitive conditions (high temperature, high concentrations of H2S, hydrocarbons, and heavy metals) for most organisms, and they are sources of new micro-organisms able to produce compounds with biotechnological potential [1,2]. Bacillus licheniformis B3-15, isolated from a shallow marine vent (Vulcano Island, Italy), has previously been reported as tolerant to arsenate (AsV) [3]. We suppose that exopolysaccharides (EPSs) play a key role in the protection in situ of bacterial cells by binding the heavy metals naturally present in shallow marine vents, therefore, in this study, we evaluated: i) the arsenic adsorption capacity of EPS B3-15 by mass spectroscopy, ii) the functional groups of the EPS interacting with the arsenate and arsenite groups by ATR-FTIR spectroscopy, and iii) the ability of the EPS to prevent arsenic toxicity, using a bioluminescent assay. The EPS, consisting mainly of repetitive disaccharide units with manno-pyranoside configuration and low protein content, was able to adsorb AsV (34.5%) more than AsIII (1.8%). as revealed by ATR-FTIR spectroscopy. The EPS functional groups involved in the adsorption of arsenic cations (–OH, C=O, C–O, and C=C) probably through changes in glycosidic bonds and ion exchanges. As result by the luminescence assay, EPS B3-15 (300 µg/mL) did not show any toxic effects and was also able to reduce more than twice the toxicity of AsIII and AsV. Due to its adsorption activity and reduction of arsenic toxicity, EPS B3-15 could be used as a novel eco-compatible polymer to develop innovative substrates functionalized with EPS for the bioremediation of arsenic-contaminated water.