Abstract
Twenty–six moderately halophilic bacteria were isolated from the sea coast of Sanya city Hainan province China, and screened for their ability to secrete halophilic proteases. Among them, a moderately halophilic strain Pontibacillus sp. SY–8 was investigated for the production of extracellular protease. 16S rRNA gene analysis identified it as Pontibacillus chungwhensis. To enhance protease production, Plackett–Burman (PB) design and response surface methodology (RSM), were used to determine the optimal concentrations. Based on PB design experiments, casein, yeast extract powder, and NaCl were determined as the main factors influencing protease production. The optimal concentration of these components was determined by response surface methodology, which is based on the central composite design. Under the proposed optimized conditions, the protease experimental yield (1441 U ml–1) closely matched the yield predicted by the statistical model (1472.59 U ml–1) with R2 =0.990. An overall 3.56–fold increase in protease production was achieved in the optimized medium as compared with the unoptimized medium.
Highlights
Microbial proteases are important class of enzymes, which constitute more than 65% of the total industrial enzyme market
Halophiles are microorganisms which grow over an extended range of salt concentrations (3–30% NaCl, w/v), include the halophilic bacteria and archaea
The exoenzymes from halophiles are interesting from the basic scientific viewpoint, but they may be of potential interest in many industrial and biotechnological applications, owing to their stability and activity at low water levels
Summary
Microbial proteases are important class of enzymes, which constitute more than 65% of the total industrial enzyme market. A challenge faced by industrial application of microbial proteases is optimal activity and stability in a wide range of salinity. Halophilic proteases, which are active both at low and high concentrations of NaCl, are needed. Halophiles are microorganisms which grow over an extended range of salt concentrations (3–30% NaCl, w/v), include the halophilic bacteria and archaea. Halophilic bacteria grow well over a wide range of salt concentrations, 3-15% [6], and sometimes even at close to saturated NaCl [5]. Their exoenzymes exhibit unique structural, biochemical characteristics, and stable under extreme high saline conditions [79]. The exoenzymes from halophiles are interesting from the basic scientific viewpoint, but they may be of potential interest in many industrial and biotechnological applications, owing to their stability and activity at low water levels
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