ABSTRACT
An alkaline protease producing strain was isolated from spoilt cottage cheese sample which was identified as Bacillus tequilensis strain SCSGAB0139 on the basis of morphological, cultural, biochemical characteristics and 16S rRNA sequence analysis. Primary screening for protease production was carried out by observing for zone of hydrolysis on skim milk agar, GYEA milk agar and gelatin agar plates. Physicochemical parameters like pH of the medium, incubation time and temperature, aeration and composition of the medium were optimized for maximum protease production by this isolate. Maximum yield of protease (85.67U/ml) was obtained in a medium containing peptone (5% w/v), maltose (5% w/v) and KNO3, 0.5%; K2HPO4, 0.4%; trisodium citrate, 0.4; CaCl2, 0.0002%; MgSO4·7H2O, 0.05%; Na2CO3, 1%.; 1% (v/v) of a trace element solution (NH4)6MO7O24, 0.01%; FeSO4·7H2O, 0.2%; CuSO4·5H2O, 0.02%; ZnCl2, 0.02%) having pH 10, inoculated with 1%(v/v) of pre-grown cell mass and incubated at 30°C on a rotary shaker (100rpm) for 48hrs. Absence of any one of the following salts viz. KNO3, K2HPO4, tri-sodium citrate; MgSO4, CaCl2 and Na2CO3 from optimized medium reduced the protease production by 80% to 40%. The enzyme has an optimum pH of 9 and maintained its stability over a broad pH range between 6 and 10. Its optimum temperature is 30°C, and exhibited a stability of up to 65°C. Among metal ions only Ca2+ and Mg2+ions enhanced the enzyme activity up to 105% and 107% respectively while other metal ions reduced the activity by 40% where as EDTA exhibited the least inhibitory effect upon the enzyme. Protease activity was enhanced in the presence of isopropanol and marginally reduced in the presence of other organic solvents studied. The crude enzyme showed stability towards various surfactants such as Tween-20, Tween- 80, SDS and Triton X-100. It also showed excellent stability and compatibility with commonly used laundry detergents (Ariel, Surf excel and Surf Blue). The enzyme retained its activity in 2% H2O2 indicating it to be bleach-stable. The present findings show that the protease from Bacillus tequilensis strain SCSGAB0139 is alkali- and detergent- stable and hence, when this protease was applied to remove blood stains from cotton fabrics indicated its potential use in detergent formulations.