Abstract
Alkaline proteases are hydrolytic enzymes that cleave peptide bonds in proteins and peptides in alkaline conditions, which occupy a pivotal importance with respect to their industrial applications. This study aimed to isolate new alkaline protease producing alkaliphilic bacteria from Egyptian soda lakes and optimize the fermentation process to enhance the enzyme production. The extensive screening process of the samples collected from Egyptian soda lakes resulted in isolation of a potent alkaline protease producing alkaliphilic strain AK-R. The isolate was identified as Bacillus agaradhaerens strain AK-R based on 16S rRNA gene analysis (99%). Wheat bran and gelatin supported maximum alkaline protease production as carbon and nitrogen sources, respectively. Strain AK-R is halo-tolerant thermo-tolerant alkaliphilic bacterium in nature, as it can grow over a wide range of NaCl concentrations (up to 25%) and up to 55 °C, with maximal growth and enzyme production at 2.5-5%, and pH 11 at 35 °C. Among the tested cations, only Mg 2+ and Ca 2+ ions significantly enhanced the enzyme production by about 1.2, and 1.3 fold compared to control, respectively. Alkaline protease secretion was coherent with the growth pattern, reaching maximal yield after about 32 h (mid stationary phase). In conclusion a new halo-tolerant thermo-tolerant alkaliphilic alkaline protease producing Bacillus agaradhaerens strain AK-R was isolated from Egyptian soda lakes. Optimization of the nutritional and cultivation conditions resulted in increase of enzyme yield by 20 fold. Strain AK-R and its extracellular alkaline protease with salt, pH and temperature, tolerance signify their potential application in laundry and pharmaceuticals industries.
Highlights
Proteases are hydrolytic enzymes that cleave peptide bonds in proteins and peptides that occupy a pivotal importance with respect to their commercial and industrial applications (JOSHI et al, 2013)
Strain AK-R is halo-tolerant thermotolerant alkaliphilic bacterium in nature, as it can grow over a wide range of NaCl concentrations and up to 55 °C, with maximal growth and enzyme production at 2.5-5%, and pH 11 at 35 °C
The results indicated that strain AK-R showed high alkaline protease activity (36.3 U/mL) and was selected for further investigation
Summary
Proteases are hydrolytic enzymes that cleave peptide bonds in proteins and peptides that occupy a pivotal importance with respect to their commercial and industrial applications (JOSHI et al, 2013). Alkaline proteases, characterized by high activity and stability in high alkaline range, have various industrial applications including leather, pharmaceuticals, foods, diagnostic reagents, soy processing, peptide synthesis, re-cycling of X-ray film for silver extraction, and bioconversion of chitinous materials (SHAH et al, 2010; JELLOULI et al, 2011; JOSHI et al, 2012). The main application of alkaline proteases is in detergent industry, accounting for approximately 30% of the total world enzyme production, which is due to the alkaline pH of laundry detergents ingredients (HADDAR et al, 2009a). The increased commercial demand for highly active alkaline proteases with high specificity and stability continues to stimulate the search for new enzymes (VIJAYARAGHAVAN; VINCENT, 2012). When searching nature for novel alkaline protease, samples from unexplored environments should be used; and one of such environments is extreme environment in which extremphilic microorganisms are enriched, i.e. halophilies, alkalophiles, thermophiles and others (HORIKOSHI et al, 2011)
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