Extracellular thermostable proteolytic activity of the milk spoilage bacterium Pseudomonas fluorescens PS19 on bovine caseins.We studied the thermostable proteolytic activity of Pseudomonas fluorescens PS19 isolated from raw bovine milk.  The heat-treated cell-free supernatant (HT-CFS) contained a thermostable protease of approximately 45 kDa, as revealed by casein zymography.  After concentration by ultrafiltration at 10 kDa, the HT-CFS showed 2 other thermostable proteolytic bands on zymogram, with molecular masses of approximately 15 and 25 kDa. 
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