Characterization of extracellular protease from halophilic microbes isolated from Bledug Kuwu, Grobogan, Central Java

High salt-tolerant extracellular protease is an enzyme that plays a crucial role in industries and requires high salt conditions. Some protease enzymes are not resistant to high salt conditions because they may denature under high salt concentrations. Halophilic microbes produce extracellular enzymes that are stable at high salts. This research has succeeded isolating several halophilic microbes capable of producing extracellular proteases from Bledug Kuwu, Grobogan, Central Java, Indonesia. Extracellular proteases producing bacteria screened with skim milk selective medium and purified with the quadrant streak method. Then, the pure isolate and the resulting extracellular protease were characterized BK1B isolate was a Gram-positive bacterium, while BK1D was a Gram-negative bacterium. BK1B isolate is a halotolerant bacterium and BK1D is a moderate halophilic bacterium. BK1B and BK1D had the largest proteolytic index values, capable of producing extracellular proteases with an optimal production time of three days and pH 6. Extracellular proteases from BK1B and BK1D worked optimally at pH 6 and temperatures of 45 and 42 °C with 2.541 and 3.505 U/mL activity and resistance to NaCl concentrations ranging from 3 - 13% NaCl. This suggests that extracellular proteases from BK1B and BK1D strains can be stable at high salt concentrations.