Bacterial keratinase: Assay development and nutritional application

The feather-degrading bacterium Bacillus licheniformis PWD-1 produces keratinase, a serine protease capable of degrading the recalcitrant keratin in feathers. Because of its unique properties, the potential uses of keratinase include industrial and agricultural applications. To facilitate the use of these enzymes, an assay was developed to specifically detect keratinolytic activity. This assay which couples keratinase with trypsin measures the release of aromatic amino acids from a feather keratin substrate. The coupled enzyme assay was correlated to both azokeratin hydrolysis and ninhydrin assays. Addition of trypsin helped to improve assay sensitivity and decrease overall variability, and to increase assay accuracy when measuring keratinase activity in high background situations.;One potential agricultural use of the keratinase produced by PWD-1 is the application to animal feeds containing feather meal. The effectiveness of keratinase addition to feather meal was evaluated by both chick growth and precision fed rooster assays. Chick growth assays determined that a crude enzyme level of 17 g (5.2 x 105 E.U.)/kg feather meal was required for optimal growth and feed efficiency when the diet contained 10% FM. Bioassays also indicate that specific fermentative conditions can affect final experimental outcome, and that a replacement of 7% dietary protein with keratinase treated feather meal can support chick performance equal to soybean meal. Precision fed rooster assays showed an increase in true amino acid digestibility for treated feather meal of approximately 7--10% over untreated feather meal.