Isolation and Characterization of Thermophilic Alkaline Proteases Resistant to Sodium Dodecyl Sulfate and Ethylene Diamine Tetraacetic Acid from Bacillus sp. GUS1

Thermophilic Bacillus sp. GUS1, isolated from  a soil  sample obtained from citrus garden, produced at least three proteases as detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and zymogram analysis. The enzymes were stable in the alkaline pH range (8.0-12.0), with the optimum temperature and pH range of the proteases being 70ºC and 6.0-12.0, respectively. All three proteases were also highly stable at 70ºC. After 60 min of incubation at 70ºC, the enzymes retained 100% of their original activities. Enzymes were mostly inhibited by phenylmethylsulfonyl fluoride (PMSF), however 80-90% enzyme activities were retained in presence of 2-mercaptoethanol and iodoacetate. Addition of SDS and ethylene diamine tetraacetic acid (EDTA) also marginally influenced protease activities, but addition of Ca2+ to the proteases did not bring about any change. The results suggeste that most of these proteases were not metalloproteases, but Ca2+-independent serine alkaline proteases.