Characterization of a salt-activated protease with temperature-dependent secretion in Stenotrophomonas maltophilia FF11 isolated from frozen Antarctic krill.

Seafood is sometimes wasted due to the growth of psychrotolerant microbes which secrete proteases and break down proteins. Stenotrophomonas maltophilia FF11, isolated from frozen Antarctic krill, grows at a wide range of temperatures and secretes more proteases at low temperatures. According to zymogram analysis, two kinds of proteases were produced from this strain. A major protease was produced largely at 15 °C, but not at 37 °C. The temperature-dependent secreted protease was purified to homogeneity. Its molecular mass was determined at 37.4 kDa and its amino acid sequence was also obtained. This protease is a member of the subtilase group according to the NCBI blast analysis. The enzyme was highly stable at high salt concentration (4 M). Interestingly, its activity increased about 1.6-fold under high salt condition. The enzyme remains active and stable in different organic solvents (50 %, v/v) such as dimethylsulfoxide, dimethyl formamide, dioxane and acetone. These properties may provide potential applications in quality control for sea foods, in protein degradation at high salt concentration, in biocatalysis and biotransformation within non-aqueous media, such as detergent and transesterification.