Extracellular Polysaccharide Synthesized by the Halophilic Bacterium Salibacterium halochares STm, Isolated from Gypsum Dunes: Production, Physicochemical Characterization and Emulsifying Properties

This study deals with the characterization of exopolysaccharides (EPS) synthesized by a halophilic bacterium Salibacterium halochares STm recently isolated from saline soil in Cuatro Cienegas Basin, Coahuila Mexico. S. halochares exhibited an EPS production of 17.38 g/L (at 72 h), using a modified ATCC 2185 culture medium (with yeast extract at 6 g/L and NaCl at 120 g/L). Chemical characterization of the EPS revealed a composition of total sugars, protein, and uronic acids contents of 83.83%, 1.59% and 2.09% (w/w), respectively. The purified EPS showed a molecular weight of 1283 kDa. Rheological studies of the EPS aqueous solutions indicated a non-Newtonian rheological behaviour which was reliably modeled by the Cross equation. The EPS showed high emulsification indexes (EI) against diverse non-polar substances and formed microemulsions with negative high zeta-potential values (up to - 46 mV). The viscoelastic behaviour data indicated the high stability of hexane-water (1:1 ratio) emulsions stabilized with EPS. The EPS retained its EI at harsh conditions of pH (4, 6.5, 7 and 12), NaCl (0, 2.0 and 4.0 M) and thermal incubation (up to 40 degrees C, 60 min). This is the first time that a Salibacterium genus member is reported as an EPS-producer. These results reveal the discovery of a novel polysaccharide with great potential for industrial applications, such as emulsion stabilizer, viscosity modifier and thickener. [GRAPHICS]

Automated summary

This study characterized the EPS synthesized by a halophilic bacterium Salibacterium halochares STm isolated from saline soil in Mexico. The EPS showed high emulsification indexes against various non-polar substances and retained stability under harsh conditions, with potential industrial applications as an emulsion stabilizer, viscosity modifier, and thickener.