| The feather keratin is not only a kind of organic pollutant to environment but also an abundant source of feedstuff protein. The feather keratin is insoluble and resistant to degradation by the common proteolytic enzymes such as pepsin, and physical or chemical treatment leads seriously to environment pollution. Therefore, the biodegradation of feather keratin using microorganisms possessing the keratinolytic activity represents an alternative and better way for improving the nutritional values of feather keratin for feedstuff and for the removal of environmental pollutant.This paper deals with the isolation and identification of a feather-degrading bacterium from soil sample, and the conditions for production of keratinolytic enzyme and the characteristics of the crude keratinase. The results were reported as follows:1. Six strains of bacteria (A,B,C,E,G,H) and three strains of antinomycetes (81,82,84) were isolated from soils, which could degrade feather keratin. Strain C of which was identified and named as Flavobacterium breve ZDM based on its morphological and physiological characteristics and G + C mol% in DNA, which had strongest capacity of degrading feather in all of the isolated strains and could grow on the medium with feather as the solecarbon, nitrogen, sulfur and energy sources. Strain ZDM could make the untreated integrated feather fibres breakdown after incubated for one day. The feather was completely disintegrated by strain ZDM after incubation for 5 d. The degrading rate reached 55.9% after incubation for 72h. All of these results indicated that strain ZDM possessed the stronger capacity of degrading feather. It, however, couldn't degrade the calamus. The optimal conditions for production of keratinase from strain ZDM were as follows, the optimal pH was 7.5. The optimal temperature and fermentation time were 35℃ and 48h, respectively. Chicken feather and duck feather showed a significant induction for keratinase production, which resulted in the increase of 11.7 folds and 9.7 folds higher, compared to the keratinase activity of the blank, respectively. Whereas nail and hair had no any induction to keratinase production. When the content of feather powder was 1.5% in medium, the enzyme activity reached at the highest one, 1.156 U/mL. The optimal inorganic nitrogen, organic nitrogen and carbon sources were (NFL HPO casein and cornmeal, respectively. K+, Mg2+, Fe3+ could significantly promote enzyme production, and Na+ showed a slightly promotion, whereas Cu2+, Zn2+ and Cr3^ inhibited the production of keratinase. Tween20 promoted keratinase production, which heightened the activity about 30%, but TweenSO showed no effect. Whereas SDS distinctly inhibited the growth of strain ZDM, the keratinase production was also did. The enzyme activity reached the highest when the volume of medium was separated approximately 75mL in a SOOmL-flask. The keratinase activity in fermented liquid was 2.77U/mL under the optimal fermentation conditions. The optimum pH and temperature for keratinolytic activity of keratinase were 8.0 and 45℃, respectively. The crude keratinase was stable at pH 7.5~ 8.0 and 20℃ 50℃. The crude keratinase represented no activity after treatment at pH below 6.0 or higher than 10.0 for SOmin. The keratinaseactivity descended sharply when treated higher than 50℃ and no activity showed after treatment at 70 for 30min. Mercaptoethanol, Mg2+ and Ca2+ were the activator for keratinolytic activity of keratinase, and Hg2+ was the inhibitor.
|
PDF Full Text Request