Composition analysis and material characterization of an emulsifying extracellular polysaccharide (EPS) produced by Bacillus megaterium RB-05: a hydrodynamic sediment-attached isolate of freshwater origin.

摘要

Aims: This work was aimed to isolate, purify and characterize an extracellular polysaccharide (EPS) produced by a freshwater dynamic sediment-attached micro-organism, Bacillus megaterium RB-05, and study its emulsifying potential in different hydrocarbon media. Methods and Results: Bacillus megaterium RB-05 was found to produce EPSs in glucose mineral salts medium, and maximum yield (0.864 g l-1) was achieved after 24-h incubation. The recovery rates of the polysaccharide material by ion-exchange and gel filtration chromatography were around 67 and 93%, respectively. As evident from HPLC and FT-IR analyses, the polysaccharide was found to be a heteropolymer-containing glucose, galactose, mannose, arabinose, fucose and N-acetyl glucosamine. Different oligosaccharide combinations namely hexose₃, hexose₄, hexose₅deoxyhexose₁ and hexose₅deoxyhexose₁pentose₃ were obtained after partial hydrolysis of the polymer using MALDI-ToF-MS. The polysaccharide with an average molecular weight of 170 kDa and thermal stability up to 180 degrees C showed pseudoplastic rheology and significant emulsifying activity in hydrocarbon media. Conclusions: Isolated polysaccharide was found to be of high molecular weight and thermally stable. The purified EPS fraction was composed of hexose, pentose and deoxyhexose sugar residues, which is a rare combination for bacterial polysaccharides. Emulsifying property was either better or comparable to that of other commercially available natural gums and polysaccharides. Significance and Impact of the Study: This is probably one of the few reports about characterizing an emulsifying EPS produced by a freshwater sediment-attached bacterium. The results of this study contribute to understand the influence of chemical composition and material properties of a new microbial polysaccharide on its application in industrial biotechnology. Furthermore, this work reconfirms freshwater dynamic sediment as a potential habitat for bioprospecting extracellular polymer-producing bacteria. This study will improve our knowledge on the exploitation of a nonconventional renewable resource, which also seems to be ecologically significant.