Effect of bioprocess parameters on alkaline protease production by locally isolated Bacillus cereus AUST-7 using tannery waste in submerged fermentation

Present study aims to enhance protease production by employing locally isolated bacterial strains using animal skin (beef) wastes as a substrate. A proximate analysis of the substrate (skin waste) was carried out to know the percentage of protein, fats, and ash. To understand the particle size, shape, and other structural changes, scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) of both untreated and treated samples were performed. The substrate showed 83.81% crude protein, 11.23% crude fat, and 4.96% ash contents. SEM and FTIR analysis revealed changes in treated samples as compared to that untreated skin waste (control). In 140 isolated strains, 60 strains showed clear zone on 1% skim milk agar medium. The selected strains were cultured for protease assay on a production medium. The maximum protease (249.65 IU/ml) producing strain was identified as Bacillus cereus AUST-7 morphologically, biochemically, and based on 16S rDNA gene sequencing. The bioprocess parameters like aeration rate, shaking speed, and incubation period were optimized in lab scale bioreactor of 1.5 L capacity. During scale-up in a bioreactor (1.5 L), 2 volumes of aeration rate per volume of liquid medium per minute (VVM) aeration, shaking speed of 500 rpm, and 24 h of incubation period yielded maximum protease (1917.5 IU/mL) under submerged fermentation. The results depicted that defatted skin waste could be utilized as a potential substrate for the cost-effective production of alkaline protease.