Quantification of thermo-halotolerant alkaline protease activity derived from Bacillus licheniformis strains isolated from extreme environments in Morocco

Abstract

Proteases; especially alkaline proteases, constitute the most used group of enzymes in industry. The wide scope of their application requires varying properties; most commonly stability throughout the conditional changes that would occur during the various industrial processes. This study aimed to identify the potentially interesting bacterial strains obtained from Moroccan extreme environment, and evaluate their proteolytic activity under the various growing conditions. In this study, the impact of temperature and salinity on the alkaline protease activity (pH 11) of 33 Bacillus strains deposited in the Moroccan Coordinated Culture Collection, which originated from the various extreme environments from Morocco, was studied. Bacterial identification to the species level was performed using 16S rRNA gene sequencing and MultiLocus Sequence Typing (MLST), a technique that is much more precise and can identify the bacteria to the strain level. Strain B950 showed a relatively stable protease activity at the tested extreme conditions (i.e., 130.8 U/ ml at 60 °C and 10 % NaCl). On the other hand, strain B961 displayed a better overall activity at either high temperature (140.8 U/ ml) or salinity (137 U/ ml); however, it was not as stable as when grown under both extreme conditions. Regarding identity of the bacterial strains, they were all representatives of Bacillus licheniformis; although B950 and B961 strains belonged to Sequence Types 3 and 5, respectively.