Keratinase production and keratin degradation by a mutant strain of Bacillus subtilis

A new feather-degrading bacterium was isolated from a local feather waste site and identified as Bacillus subtilis based on morphological, physiochemical, and phylogenetic characteristics. Screening for mutants with elevated keratinolytic activity using N-methyl-N＇-nitro-N-nitrosoguanidine mutagenesis resulted in a mutant strain KD-N2 producing keratinolytic activity about 2.5 times that of the wild-type strain. The mutant strain produced inducible keratinase in different substrates of feathers, hair, wool and silk under submerged cultivation. Scanning electron microscopy studies showed the degradation of feathers, hair and silk by the keratinase. The optimal conditions for keratinase production include initial pH of 7.5, inoculum size of 2% （v/v）, age of inoculum of 16 h, and cultivation at 23 ℃. The maximum keratinolytic activity of KD-N2 was achieved after 30 h. Essential amino acids like threonine, valine, methionine as well as ammonia were produced when feathers were used as substrates. Strain KD-N2, therefore, shows great promise of finding potential applications in keratin hydrolysis and keratinase production.

Purification and characterization of keratinase from a new Bacillus subtilis strain

The aim of this study was to purify and characterize a keratinase produced by a new isolated Bacillus subtilis KD-N2 strain. The keratinase produced by the isolate was purified using ammonium sulphate precipitation, Sephadex G-75 and DEAE (diethylaminoethyl)-Sepharose chromatographic techniques. The purified enzyme was shown to have a molecular mass of 30.5 kDa, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The optimum pH at 50 °C was 8.5 and the optimum temperature at pH 8.5 was 55 °C. The keratinase was partially inactivated by some metal ions, organic solvents and serine protease inhibitor phenylmethanesulfonyl fluoride (PMSF). Sodium dodecyl sulfate (SDS) and ethylene diamine tetraacetic acid (EDTA) had positive effect on the keratinase activity. Reducing agents including dithiothreitol (DTT), mercaptoethanol, L-cysteine, sodium sulphite, as well as chemicals of SDS, ammonium sulfamate and dimethylsulfoxide (DMSO) stimulated the enzyme activity upon a feather meal substrate. Besides feather keratin, the enzyme is active upon the soluble proteins ovalbumin, bovine serum albumin (BSA), casein and insoluble ones as sheep wool and human hair. Calf hair, silk and collagen could not be hydrolyzed by the keratinase.