Study on isolation and identification of protease-producing marine bacteria and optimization of fermentation medium

18 strains of protease-producing marine bacteria were isolated from the South China deep sea mud by casein medium.Among them, C-7 was selected based on its higher protease activity and it was identified as Bacillus thuringiensis strain by morphological observation, physiological and biochemical experiments and 16S rDNA sequence analysis.The optimal reaction temperature of the protease was 50℃ and the optimal reaction pH was 7, which showed that it was mesophilic neutral protease.The protease had good salt- tolerance, 43% protease activity was still remained in 15% NaCl.The culture medium was as follows:5.0g glucose, 10.0g peptone, 0.5g KH2 PO4, 0.3g MgSO4 ·7H2 O, 1.0g CaCl2, 1.5g Tween-80, 1L distilled water, pH7.2.