A novel exopolysaccharides from nitrogen fixing acetic acid bacterium, Nguyenibacter vanlangensis AR-R3

An acetic acid bacterium, Nguyenibacter vanlangensis AR-R3 was isolated from rice rhizosphere and exhibited nitrogen fixation as well as plant growth promotion properties. In addition, the bacterium can produce exopolysaccharides (EPS) to promote nitrogenase activity in the bacterial cells. These research objectives were aimed to purify and characterize EPS generated from an acetic acid bacterium, N. vanlangensis AR-R3. The pure culture was inoculated in Glucose-Yeast Extract-Peptone (GYP) medium broth (2% Glucose, 0.5% Yeast Extract, and 1% Peptone). The obtained culture supernatant was concentrated using a rotary evaporator, and then crude exopolysaccharides were precipitated with absolute ethanol. Crude polysaccharides were further purified via DEAE- Sephacel Column Chromatography and Sephacryl^TM S-400 Column Chromatography, respectively. According to the results of the study, exopolysaccharides purified from N. vanlangensis AR-R3 exhibited 4 average molecular weight sizes (Mw) of 2.180 x 10⁸, 5.638 x 10⁶, 5.523 x 10⁵ and 1.990 x 10⁵ Da, respectively. Sugar composition analysis of all 4 polysaccharides revealed the same composition of two types of monosaccharides: glucose and mannose. Regarding to purified exopolysaccharides from N. vanlangensis AR-R3 had molecular weights and monosaccharide compositions difference from other acetic acid bacteria reported so far. Thus, exopolysaccharide purified in this research would be a novel polysaccharide.