Extracellular serine proteases produced Thermoactinomyces by strains from hot springs and soils of West Anatolia

Hot spring environments in West Anatolia were exploited to search for protease-producing thermophilic actinomycetes. A total of 163 thermophilic actinomycetes strains isolated from water, sediment and soil samples of 28 different hot springs were used in this study. These isolates were screened for extracellular protease production in actinomycetes isolation agar containing 1% (w/v) casein. The best five producers were selected and further studies were carried out on these strains. Thermostability, pH and temperature profiles were determined using crude enzyme preparations. In addition, the effects of various inhibitors, heavy metals, denaturants and organic solvents on the crude enzyme preparations were tested. All preparations were found to be quite thermostable. While the crude enzyme from strain 40-5 had 90.7% relative activity at 70A degrees C for 2 h, the crude enzyme from strain 51-9 retained 96.5% activity under the same conditions. Moreover, the crude enzymes were inhibited by phenylmethylsulfonyl fluoride, but activated by the presence of Mn2+ and Cu2+ divalent cations, and were found to be stable in the presence of urea, H2O2 and several organic solvents. The protease from strain 40-5 was purified and found to be a 28 kDa single protein. The five strains selected are thus promising thermostable alkaline protease producers for industrial use.