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

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°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.