Production and Characterization of Alkaline Protease from a High Yielding and Moderately Halophilic Strain of SD11 Marine Bacteria

A marine bacterium SD11, which was isolated from sea muds (Geziwo Qinhuangdao Sea area, China), was used to produce thermostable alkaline serine nonmetal protease in the skim milk agar plate medium with 10% NaCl. The optimal temperature about the manufacture of the extracellular protease was ~60°C. The crude enzyme was stable at 20–50°C. The activity was retained to 60% and 45% after heating for 1 h at 60 and 70°C, respectively. The protease was highly active in a wide pH scope (8.0–10.0) and maximum protease activity exhibited at pH 10.0. The activity was restrained by phenylmethylsulfonyl fluoride (PMSF) but mildly increased (~107%) in the presence of ethylenediaminetetraacetic acid (EDTA), indicating that the production contains serine-protease(s) and nonmetal protease(s). Moreover, the crude alkaline protease was active with the 5 mM Ca2+, Mn2+, Zn2+, Cu2+, Na+, and K+that existed separately. In addition, the protease showed superduper stability when exposed to an anionic surfactant (5 mM SDS), an oxidizing agent (1% H2O2), and several organic solvents (methanol, isopropanol, and acetone). These results suggest that the marine bacterium SD11 is significant in the industry from the prospects of its ability to produce thermally stable alkaline protease.