Effect of Medium Composition on Commercially Important Alkaline Protease Production by Bacillus licheniformis N-2

Muhammad Nadeem¹*, Javed Iqbal Qazi², Shahjahan Baig¹ and Qurat-ul-Ain Syed<sup>1

1</sup>Food and Biotechnology Research Center, Pakistan Council of Scientific and Industrial Research (PCSIR), Laboratories Complex, PK-54600 Lahore, Pakistan
²Department of Zoology, New Campus, University of the Punjab, PK-54590 Lahore, Pakistan

Article history:
Received August 18, 2007
Accepted January 1, 2008

Key words:
alkaline protease, surfactant and oxidant stability, B. licheniformis N-2

Summary:
Protease production by alkalophilic B. licheniformis N-2 was investigated in 50 mL of the growth medium consisting of (in g/L): glucose 10.0, soybean meal 10.0, K₂HPO₄ 3.0, MgSO₄·7H₂O 0.5, NaCl 0.5 and CaCl₂·2H₂O 0.5 at pH=10. Different carbon and nitrogen sources in the form of fine powder of organic, inorganic and defatted meals were studied to select the suitable substrate for alkaline protease production. The highest level of alkaline protease (677.64 U/mL) was obtained in the medium containing glucose followed by soluble starch and wheat bran. Among various nitrogen sources, defatted soybean meal was found to be the best inducer of alkaline protease, while inorganic nitrogen sources in the form of ammonium salts repressed the enzyme activity up to 96 %. Thermostability studies showed that the enzyme in the presence of 10 mM Ca²⁺ ions retained its residual activity up to 80 % even after incubation at 40 °C for 12 h. The enzyme was found stable over a broad range of pH (8–11) and lost 52 % of its residual activity at pH=12. After the treatment with Tween 20, Tween 45, Tween 65, Triton X-405, H₂O₂ and sodium perborate, each at 1.0 % concentration, the enzyme showed residual activity of 105, 82, 116, 109, 135 and 126 %, respectively. The application of alkaline protease for removal of blood stains from cotton fabric also indicates its potential use in detergent formulations.

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