Biosynthesis of alkaline protease by alkaliphilic Bacillus sp. NPST-AK15 cells immobilized in gel matrices

Abstract

Background and objectives Proteases are an important group of hydrolytic enzymes catalyzing the hydrolysis of various proteins by cleavage of the peptide bonds between the amino acids residues. Proteases have applications in several fields including medical and pharmaceuticals industries. Bacterial cell immobilization by entrapment techniques is one of the most effective approaches used in biotechnology at laboratory and industrial scale. Herein, we report the production of alkaline protease by immobilized halotolerant alkaliphilic Bacillus sp. strain NPST-AK15 cells in batch and repeated batch fermentation.Materials and methods Alkaline proteases-producing halotolerant alkaliphilic Bacillus sp. strain NPST-AK15 (accession no. KP295749) was previously isolated from hypersaline soda lakes, located at Wadi El- Natrun Valley (Egypt). Three different matrices were tested for immobilization of Bacillus sp. strain NPST-AK15 whole cells by entrapment technique including alginate, gelatin, and agar gel.Results and discussion Among various matrices tested for whole cell immobilization of Bacillus sp. NPST-AK15, alginate was found to be the best matrix for cell entrapment and alkaline protease production, showing the highest specific productivity (3214.34 U/g wet cells/h) and enzyme production (923.4 U/ml), followed by cells immobilized in agar and gelatin. Furthermore, the production of alkaline protease by Bacillus sp. NPST-AK15 immobilized in alginate gel was enhanced by investigation of the influence of various parameters on alginate beads preparation including alginate concentration, bead size, and biomass loading. Maximum enzyme production (1020.1 U/ml) and specific productivity (4086.9 U/g wet cells/h) were achieved using alginate concentration of 3.0% (w/v), bead diameter of 3.5 mm, and cell loading of 0.50 g wet weight of cell biomass per 0.3 g of sodium alginate. The immobilized Bacillus sp. NPST-AK15 cells exhibited operation stability in repeated batch fermentation, retaining 89.1 and 61.3% of its productivity after five (120 h) cycles and 10 (240 h) cycles, respectively.