Abstract:To obtain Serratia marcescens capable of producing serratiopeptidase，a red-pigment-producing strain isolated using a tyrosine-supplemented screening medium was subjected to morphological，physiologicalbiochemical，and molecular biological identification. The strain was identified as Serratia marcescens and designated as S. marcescens Cczu.wj01. When cultured in the initial screening liquid medium，the strain exhibited an enzyme activity of 23.44 U/L. To further explore its enzyme-producing potential，the fermentation conditions were optimized. The optimal medium composition for Cczu. wj01 was determined as follows：malt extract 5 g/L，soy peptone 3 g/L，sodium chloride 10 g/L，and dipotassium hydrogen phosphate 10 mmol/L. The optimal fermentation conditions were an initial pH of6.5，a seed age of 12 h，an inoculum size of0.2%，a culture temperature of 31 ℃，and a shaking speed of 160 r/min. After 16 h of cultivation under the optimized conditions，the serratiopeptidase activity of strain Cczu.wj01 reached 316.42U/L.