Abstract
A Gram-positive, rod-shaped, spore-forming haloalkaliphilic bacterium designated as NA7 was isolated from the surface of a Helianthemum nummularium root sample obtained from Wadi Natrun in Egypt. Sequence analysis of the 16S rRNA gene revealed a Bacillus haloalkaliphilius strain as the closest match with 99% identity. In a shake flask culture containing 10% NaCl, adjusted to pH 10 and incubated at 37°C, the isolated strain produced thermostable extracellular alkaline protease with relatively stable maximum activity records (0.610-0.625 TU) within a relatively long stationary phase that exceeded 60 h. A 2-level fractional factorial design (Plackett-Burman) was then applied to screen for nutritional and cultivation factors regulating protease production by the isolate and to appraise their effects. Calculated statistical parameters revealed that NaCl and MgSO4 are the most significant independent variables affecting alkaline protease production by NA7 and suggested a near-optimum culture condition. Verification of this predicted condition resulted in an alkaline protease specific activity record of 509 TU/mg protein with a 1.27 fold increase when compared to the basal medium culture. Key words: Alkaline protease, Bacillus haloalkaliphilus, Wadi Natrun, haloalkaliphiles.
Highlights
Bacteria are by far the most popular source of commercial alkaline proteases
A Gram-positive, rod-shaped, spore-forming haloalkaliphilic bacterium designated as NA7 was isolated from the surface of a Helianthemum nummularium root sample obtained from Wadi Natrun in Egypt
Verification of this predicted condition resulted in an alkaline protease specific activity record of 509 tryptic units (TU)/mg protein with a 1.27 fold increase when compared to the basal medium culture
Summary
Bacteria are by far the most popular source of commercial alkaline proteases. Bacterial alkaline proteases are characterized by their broad substrate specificity, high activity at alkaline pH and an optimal temperature around 60°C (Rao et al, 1998). Thermophilic and alkaliphilic bacilli produce alkaline proteases that can considerably withstand high temperatures, alkaline pH and chemical denaturing agents (Johnvesly and Naik, 2001; Sai‐Ut et al, 2015). Enzymes such as alkaline proteases, alkaline amylases, and alkaline cellulases expressed by alkaliphilic microorganisms have been extensively investigated and set to be used on industrial scales (Takami et al, 2000; Mokashe et al, 2015), there are no reports describing the expression of alkaline protease by a Bacillus haloalkaliphilus
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