Purification anc characterization of a keratinase from a feather-degrading bacterium, Bacillus sp. SH-517

Abstract

We isolated Bacillus sp. SH-517 from decomposed chicken feathers at a local poultry plant. This strain produced a keratinase that degrades poultry feathers and therefore will be very valuable for industrial use. Most feathers were degraded by the strain within 40 h at 40°C by shaking culture (180 rpm). The keratinase from the culture medium of Bacillus sp. SH-517 was purified by centrifugation, 30？80% ammonium sulfate fractionation, twin-column DEAE-cellulose ion exchange chromatography and Sephadex G-150 gel filtration, to obtain a purified keratinase at 10.82% yield and 14-fold overall purification. The purified enzyme had a specific activity of 825 U/mg. A single protein band was shown on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weight of the keratinase from Bacillus sp. SH-517 was estimated as 51 kDa. The optimum pH and temperature for the enzyme reaction were 7.5 and 40°C, respectively. The enzyme remained stable over the pH range from 4.0 to 9.0 and at temperatures below 50°C. Proteins such as milk casein and chicken feathers were easily hydrolyzed by this enzyme. The enzyme activity was significantly inhibited by Hg2+, Ag2+, ethylene diamine tetraacetic acid (EDTA) and ethylene glycol tetraacetic acid (EGTA), but slightly stimulated by K+ and Na+.