Abstract: The purpose of the experiment was to identify protopectinase-producing bacteria X4 by molecular biology methods. To improve productivity of protopectinase, the X4 medium was optimized using a response surface method with enzyme activity as the index. The final result of X4 was Bacillus polyfermenticus. Starch, yeast extract and tryptone were found to be the main influencing factors. The optimal formula of the medium was determined: starch 3.45 g/L, yeast extract 3.29 g/L, and tryptone 5.68 g/L. The final activity of protopectinase was 51.35 U/mL, which was 2.74 times before optimization.

Key words: medium, optimization, protopectinase, response surface, strain identification