Production and characterization of a bioactive extracellular homopolysaccharide produced by Haloferax sp. BKW301.

The production of extracellular polysaccharides (EPS) by haloarchaeal members, with novel and unusual physicochemical properties, is of special importance and has the potential for extensive biotechnological exploitation. An extremely halophilic archaeon, Haloferax sp. BKW301 (GenBank Accession No. KT240044) isolated from a solar saltern of Baksal, West Bengal, India has been optimized for the production of EPS under batch culture. It produced a considerable amount (5.95 g/L) of EPS in the medium for halophiles with 15% NaCl, 3% glucose, 0.5% yeast extract, and 6% inoculum under shake flask culture at 120 rpm. The purified EPS, a homopolymer of galactose as revealed by chromatographic methods and Fourier-transform infrared spectroscopy, is noncrystalline (CIxrd , 0.82), amorphous, and could emulsify hydrocarbons like kerosene, petrol, xylene, and so forth. Moreover, the polymer is highly thermostable (up to 420°C) and displayed pseudoplastic rheology. Biologically, the EPS was able to scavenge DPPH (2,2-diphenyl-1-picrylhydrazyl) radical efficiently and inhibit the proliferation of the Huh-7 cell line at an IC50 value of 6.25 µg/ml with a Hill coefficient of 0.844. Large-scale production of this thermostable, pseudoplastic homopolysaccharide, therefore, could find suitable applications in industry and biotechnology.

Partial characterization of an extracellular polysaccharide produced by the moderately halophilic bacterium Halomonas xianhensis SUR308.

A moderately halophilic bacterium, Halomonas xianhensis SUR308 (Genbank Accession No. KJ933394) was isolated from a multi-pond solar saltern at Surala, Ganjam district, Odisha, India. The isolate produced a significant amount (7.87 g l(-1)) of extracellular polysaccharides (EPS) when grown in malt extract-yeast extract medium supplemented with 2.5% NaCl, 0.5% casein hydrolysate and 3% glucose. The EPS was isolated and purified following the conventional method of precipitation and dialysis. Chromatographic analysis (paper, GC and GC-MS) of the hydrolyzed EPS confirmed its heteropolymeric nature and showed that it is composed mainly of glucose (45.74 mol%), galactose (33.67 mol %) and mannose (17.83 mol%). Fourier-transform infrared spectroscopy indicated the presence of methylene and carboxyl groups as characteristic functional groups. In addition, its proton nuclear magnetic resonance spectrum revealed functional groups specific for extracellular polysaccharides. X-ray diffraction analysis revealed the amorphous nature (CIxrd, 0.56) of the EPS. It was thermostable up to 250 °C and displayed pseudoplastic rheology and remarkable stability against pH and salts. These unique properties of the EPS produced by H. xianhensis indicate its potential to act as an agent for detoxification, emulsification and diverse biological activities.