Characteristics of a novel bacterial polysaccharide consisted of glucose and mannose as major components

A bacterial strain, designated KMBL 5781, producing a high level of extracellular biopolymer was isolated from soil and identified as Mitsuaria chitosanitabida based on the 16S rRNA gene sequences. The biopolymer was purified by the sequential precipitation using ethanol, cethyl trimethyl ammonium bromide and then ethanol again. Its molecular weight was estimated to be about 54.7 kDa by the MALDI-TOF analysis. GC–MS analysis revealed that it is a polysaccharide consisting of glucose, mannose and galactose with approximate molar ratio of 18:6:1. In lower concentrations such as 0.5% and 1% viscosities of the EPS solution was higher than that of the xanthan gum used as a control. At the final range of shear rate the viscosity of 0.5% EPS was 34 cP while 0.5% xanthan showed 19.8 cP. The 1% EPS solution at the same rate has shown 59 cP and the viscosity of 1% Xanthan was 35 cP. When heated from 20 to 92 °C, the EPS solution (2%) remain stable from room temperature until 60 °C and showed significantly higher viscosity at 92 °C than 2% xanthan. The EPS hydrogel (2%) was strongly stable, which released no water during the incubation at 4 °C for 20 days and even after the tubes containing the gel was centrifuged at 4000× g for 10 min. Addition of the EPS into the starch solution resulted in the increase the weight and volume of the gel.