Highly active and stable protease production by an extreme halophilic archaeon Haloarcula sp. TG1 isolated from Lake Tuz, Turkey

Objective Isolation of halophilic microorganisms from Çankırı salt mine and Lake Tuz in Turkey to explore versatile protease producers for industry and characterization of protease enzyme from the best protease producer among the isolated strains. Methods Extreme halophiles were isolated from salt samples of Çankırı salt mine and Lake Tuz. Their protease activities were determined. The isolate with the highest protease activity was characterized. Its protease activity was evaluated in different NaCl concentrations, temperature and pH ranges, and in the presence of different inhibitors and metals. Thermostability and pH stability were also determined. Results The highest protease producer strain was identified as Haloarcula sp. on the basis of 16S rRNA analysis. The isolate namely, Haloarcula sp. TG1, was found to be 99% identical to Haloarcula salaria strain HST01-2R. The TG1 protease was found to possess very high activity and stability over a broad pH and temperature ranges. Its maximum activity was recorded at pH: 4.0, 50°C and 4 M NaCl. Among inhibitors tested, dimethyl sulfoxide (DMSO) and ethanol caused the highest decrease (ca. 25%) in its activity. Conclusion Due to the high activity and stability over a wide range of extreme conditions, Haloarcula sp. TG1 protease reported here is a promising candidate in biotechnology.