Abstract
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.
Highlights
Protease and other carbohydrate-hydrolyzing enzymes are the most important among industrial enzymes and have been researched widely
Total 116 bacteria were obtained from sea muds obtained, but only 14 strains could form a clear zone of hydrolysis of skimmed milk powder on the agar plate
Strain SD11 was selected for all subsequent researches
Summary
Protease and other carbohydrate-hydrolyzing enzymes are the most important among industrial enzymes and have been researched widely. Proteases constitute one of the third largest groups of enzymes in industry [1, 2], with two-thirds of the proteases produced by microorganisms commercially [3]. They are used in all kinds of industrial situations such as pharmaceuticals, drug manufacturing, detergents, surface cleaning formulations, waste treatment, silver recovery, digestive supplements, agrochemical additives, and diagnostic reagents [4,5,6]. Bacteria are the most primary species of alkaline protease generators and Bacillus genus is the most dominant source [5, 8,9,10]. Proteases from microorganisms especially from Bacillus sp. are the most extensively developed industrial proteases that have been used mainly in detergent formulations [11, 12]
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