Characterization of haloglycan, an exopolysaccharide produced by Halomonas stenophila HK30

We have conducted a thorough study of the exopolysaccharide (EPS) produced by strain HK30 of Halomonas stenophila, which we have named haloglycan. This strain was chosen during an ongoing research programme aimed at finding novel exopolysaccharide-producing halophilic bacteria in unexplored hypersaline habitats. Strain HK30 was isolated from a saline-wetland in Brikcha (Morocco) and identified as belonging to the species H. stenophila. It produced EPS mainly during the exponential growth phase and to a lesser extent during the stationary phase. Culture parameters influenced both bacterial growth and EPS production, EPS yield always being directly related to the quantity of biomass. Under optimum culture conditions, strain HK30 produced 3.89 g of EPS per litre of medium. The polymer was a sulphated heteropolysaccharide composed of two fractions, with molecular masses of 8.2 × 104 and 1.4 × 106. The crude EPS contained 44 ± 0.1% w/w carbohydrates and the following monosaccharide composition: glucose (24 ± 1.73), glucuronic acid (7.5 ± 0.37), mannose (5.5 ± 0.17), fucose (4.5 ± 0.36), galactose (1.2 ± 0.17) and rhamnose (1 ± 0.05) (%, w/w). It produced solutions of high viscosity and pseudoplastic behaviour that showed interesting flocculating and emulsifying activities and was also involved in forming biofilm.