Wealth from waste: Optimized alkaline protease production from agro-industrial residues by Bacillus alcalophilus LW8 and its biotechnological applications

Abstract

An efficient alkaline protease producer was isolated from the water of the hyperalkaline-saline Lonar soda lake and identified as Bacillus alcalophilus LW8 by culture-dependent techniques by its morphological, microscopic, biochemical, physiological and molecular characteristics. The 16S rRNA gene sequence was submitted to the GenBank nucleotide repository under accession number KC689353. Alkaline protease production was optimized by adopting a one-variable-at-a-time approach in a submerged fermentation system in modified fermentation medium (MFM). The optimized components of MFM were (w/w) casein (1%), sugarcane molasses (1%), NaCl (1%), ammonium sulphate (0.5%), KH2PO4 (0.05%), K2HPO4 (0.05%) and Na2CO3 (1%). Optimized culture conditions were used for alkaline protease production. The final yield of partially purified alkaline protease after dialysis was 53.35%. The molecular mass of the dialysed alkaline protease was 27kDa. On a Lineweaver–Burk plot, the calculated Km and Vmax values were 24mg/mL and 1000U/mg, respectively. The enzyme was remarkably stable in the pH range 7.0–12.0, with optimum activity at pH 10.0. LW8 alkaline protease was completely inhibited by phenylmethylsulphonyl fluoride at 10mmol/L, indicating that the enzyme belongs to the serine protease class. The metal ions Ca2+, Ba2+, Mg2+, Zn2+, Fe3+, Cu2+ and Mn2+ increased the catalytic activity of partially purified alkaline protease. The protease effectively decomposed the gelatinous coating on an X-ray film, hydrolysed blood clot, a blood-stain from a piece of cotton fabric and hairs from a piece of goat skin.