Abstract: Aureobasidium pullulans AP8, an original strain conserved in our laboratory, was treated with both EMS (ethyl methyl sulfonate) and UV (ultraviolet) to screen a high yield strain for pullulan production. The best mutation results were obtained through EMS treatment for 40—60 min at a final concentration of 0.4 mol/L followed by UV irradiation for 1.5—2.5 min at a distance of 30 cm. A genetically stable mutant named as UV60 was obtained which is high in pullulan production (22.1 g/L) and low in pigment content. The mutant strain was markedly superior to the starting strain AP8 in terms of colony color, size and texture as well as fermentation performance. Using one-factor-at-a-time and orthogonal array design methods, the optimal shake fermentation medium for this mutant to produce pullulan was composed of 50.0 g/L sugar, 1.5 g/L yeast extract, 1.5 g/L NaCl, 0.3 g/L MgSO4, 2.0 g/L K2HPO4 and 0.7 g/L (NH4)2SO4, resulting in a pullulan yield of 27.24 g/L and a conversion rate of 54.48% for polysaccharides.

Key words: Aureobasidium pullulans, mutation, polysaccharide, fermentation