Abstract: Xanthomonas campestris was used as the starting strain for the screening of xanthan gum-producing strain by atmospheric room temperature plasma (ARTP) mutagenesis. The results showed that five mutated strains were obtained based on the diameter of colony on primary screening plate. Then, one excellent strain X20 was found by evaluating the yield and viscosity of xanthan gum for further secondary screening. The xanthan gum yield and viscosity of strain X20 were 3.52 g/L and 77.30 mPa·s, which were 77.78% and 40.03% higher than that of the starting strain, respectively. After 10 generations of cultivation, strain X20 exhibited good genetic stability. Different environmental factors affecting the fermentation performance of strain X20 were studied. When glutamic acid was used as the nitrogen source, the highest xanthan gum production and viscosity were 7.30 g/L and 495.50 mPa·s, respectively, which were 43.27% and 22.29% higher than those of the starting bacteria. High concentration of glutamic acid (>1 g/L) significantly suppressed the fermentation culture viscosity of the starting strain and X20, which reduced to 21.8 mPa·s and 25.93 mPa·s at 4 g/L glutamic acid, respectively. Xanthan gum viscosity of strain X20 was higher than that of the starting strain under different initial pH conditions. Moreover, strain X20 was more adapted to the fermentation environment of pH 6.5 (with viscosity of 546.5 mPa·s). With the increase of salinity, the xanthan gum yield of strain X20 increased while its viscosity decreased, but all of them were higher than those of the starting strain. When the salinity was 8 g/L, the xanthan gum yield and viscosity of X20 were 12.19 g/L and 331.23 mPa·s, which were 23.05% and 109% higher than those of the starting strain, respectively. The viscosity of X20 remained stable at different temperatures (20 ℃-80 ℃) and high mineralization (28.90 g/L), and was always better than that of the starting strain, showing some potential for industrial application.

Key words: xanthan gum, Xanomonas campestris, ARTP mutagenesis, viscosity, stability