A novel low molecular weight extracellular protease from a moderately halophilic bacterium Salinivibrio sp. strain MS-7: production and biochemical properties

Kinetics of bacterial growth and protease production were monitored on a novel isolated moderately halophilic bacterium, Salinivibrio sp. strain MS-7, and maximum growth and protease activity was achieved after 48 hours at 30 degrees C and 180 rpm. To determine the effect of various carbon sources on protease production, glucose, lactose, sucrose and maltose were investigated and maximum production of the enzyme was obtained in a basal medium (pH 8.0) containing maltose as a carbon source (494 U/ml). The protease was isolated from a stationary phase culture, purified 3.6-fold with 56% yield by a simple procedure and characterized biochemically. The enzyme revealed a monomeric structure with a relative molecular mass of 21 KDa by running on SDS-PAGE. Maximum caseinolytic activity of the enzyme was observed at 50 degrees C, pH 8.0 and 0-0.5 M NaCl with a high tolerance to salt concentrations of up to 3 M. The effect of various metal ions and inhibitors on caseinolytic activity of the purified protease revealed that it probably belongs to the subclass of serine metalloproteases. These findings suggest that the protease secreted by Salinivibrio sp. strain MS-7 can be introduced as a candidate for biotechnological applications based on its haloalkaline properties.