Partial characterization and flocculating behavior of an exopolysaccharide produced in nutrient-poor medium by a facultative oligotroph Kiebsiella sp. PB12(ENVIRONMENTAL BIOTECHNOLOGY)

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A facultative oligotrophic strain from the water sample of River Mahananda, Siliguri India was selected for its property to produce exopolysaccharide (EPS) in nutrient-poor (oligotrophic) medium. Viability assay of the strain was performed in sterile liquid LB, R2A, river water and diluted (10^<-3>) LB at 30℃ and pH 7 to understand oligotrophy. The selected strain was identified by 16S rRNA gene sequencing and designated as Klebsiella sp. PB12. Phylogenetic analysis showed its closest relationship with Klebsiella variicola ATCC BAA-830^T. Purification of EPS was performed by ethanol precipitation, dialysis and freeze-drying. Chemical analysis revealed that purified EPS was mainly composed of 72.32% (w/w) neutral sugar and 14.12% (w/w) uronic acids. Fourier transform infrared (FT-IR) spectroscopy indicated the presence of hydroxyl, carboxylic and methoxyl functional groups. The optimal dosages for flocculation of activated carbon suspension were 17 mg/l EPS and 4 mM CaCl_2. EPS showed fiocculating rate of above 80% over a wide range of pH (pH 3-10) whereas, more than 90% rate was noted in the temperature range (10-50℃) tested in presence of CaCl_2. Moreover, EPS showed characteristic emulsifying activity with toluene (66.6%), n-hexadecane (65%), olive oil (63.3%) and kerosene (50%). The apparent molecular weight of the EPS was 〜2 x 10^5 Da.
2013-01-00