This study was conducted under in vitro conditions to assess the effect of culture conditions on the protease production of Streptomyces DH3.4. Experiments were conducted in various pH levels (4, 5, 6, 7, 8 9) and different concentrations of NaCl (0; 0.5; 1; 1,5; 2; 2.5; 3 and 3.5%). The incubation time in the experiment was observed at intervals of 24, 48, 72, 96, 120, 144 and 168 hours. The sources of carbon used in the experiment were glycerol, D-glucose, sucrose, D-maltose, D-xylose, soluble starch with a concentration of 1%. Organic nitrogen sources were chosen such as casein, malt extract, peptone, tryptone, soybean meal, and yeast extract with a concentration of 0.5%. The sources of inorganic nitrogen including KNO₃, (NH₄NO₃), (NH₄)₂SO₄ and NH₄Cl were designed with a concentration of 0.1%. Each experiment was run in triplicates. The results showed that the maximum protease production from Streptomyces strain DH3.4 was found under culture conditions adjusted to pH7.0, 1.5% NaCl and 144 hours of incubation. Starch performed the sole source of carbon, whereas malt extract and (NH₄)₂SO₄ were the superior organic and inorganic substrates, respectively.

Keywords: NaCl, pH, Streptomyces, Carbon source, nitrogen source, protease enzyme