Abstract:

For the purpose of increasing the production of microbial polysaccharide gum, strain FJAT-10151, which showed
a productivity of 8.65 g/L, was screened from 22 bacterial isolates conserved in our laboratory, which have been reported
for the production of polysaccharide gum. The selected isolated was identified as Xanthomonas axonopodis by 16S rDNA
sequence analysis. By morphology observation, physiological and biochemical tests and Gram staining, it was further
identified as a Gram negative strain, and its colonies were small, round, yellowish, opaque and mobile, having a smooth,
moist and slightly bulge surface and regular edge. Polysaccharide gum was isolated from the fermentation broth of the
strain in water extraction and alcohol precipitated. As determined by phenol-sulfuric acid method, carbazole method and
Coomassie brilliant blue method, the contents of neutral saccharide, acidic saccharide and protein in the exopolysaccharide
gum were 36.81%, 8.90% and 15.27%, respectively. The polysaccharide gum was deproteinized by the Sevage method
and then completely hydrolyzed for gas chromatography-mass spectrometry (GC-MS) analysis after derivatization to
aldononitrile acetates. The analysis indicated that it mainly consisted of glucose and mannose at a molar ratio of 1:1.12.
It was identified by FTIR, UV spectroscopy and GC-MS as a xanthan. Gelation properties of the polysaccharide gum
were tested by viscosity and texture profile analysis (TPA). The viscosity of 1 g/100 mL polysaccharide gum solution was
408 mPa·s at 60 r/min. The TPA results indicated that the polysaccharide gum extracted from Xanthomonas axonopodis
FJAT-10151 had excellent gel properties with the smallest hardness, better elasticity and stickiness, and the best
adhesiveness and chewiness compared with commercial gellan and xanthan. In conclusion, this Xanthomonas axonopodis
strain has potential applications.

Key words: Xanthomonas axonopodis, xanthan, gumminess