Abstract
Bacillus subtilis S1-4, isolated from chicken feather could efficiently degrade feathers by secreting several extracellular proteases. In order to get insight into the individual protease involved in keratin hydrolysis, a keratinase designed as BsKER71 was cloned and expressed in Bacillus subtilis WB600. In silico analysis revealed that BsKER71 protein contained a mature protein of 36.1 kDa. Further, purified BsKER71 could hydrolyze a variety of natural proteins, such as fibrous protein, collagen protein, casein, keratin and bovine serum albumin. In addition, this keratinase exhibited high enzyme activity in a wide range of pH and optimal pH of 10.0 and 9.0 in the hydrolysis of casein and keratin, respectively. Similarly, the optimal temperature was 55 °C and 50 °C for the hydrolysis of above two substrates, respectively. The hydrolytic activity was significantly inhibited by phenylmethanesulfonyl fluoride (PMSF), indicating the presence of serine residue in the active site. Moreover, ethylenediaminetetraacetic acid (EDTA) and phenanthroline moderately inhibited the hydrolytic activity. The catalytic activity was stimulated by Mg2+ and Ca2+, but greatly inhibited by Cu2+. Furthermore, several chemicals exhibited different effects on the hydrolysis of casein and keratin by BsKER71. These results provided a better understanding of BsKER71 from feather degrading bacterium B. subtilis S1-4.
Highlights
Keratin is the key structural component of outer coat of feather, hair, nail, horn, hoof and skin of animals
Enzymatic degradation of feathers provides an attractive method for degradation of keratin to value-added products like amino acids, nitrogen fertilizers or feed supplements which can be used as feed supplement or organic fertilizer (Bhari et al 2018)
A new B. subtilis strain S1-4 was isolated from chicken feathers, which could secrete several keratinases to efficiently degrade the feathers
Summary
Keratin is the key structural component of outer coat of feather, hair, nail, horn, hoof and skin of animals. 7.3 cysteine residues are present per 100 residues in feather keratin (Sahni et al 2015). The high proportion of cysteine is the result of high degrees of cross-linking for keratin protein. Microbial enzymes have been used for bio-processing of poultry waste, which provided an economic and environment-friendly strategy for the utilization of feather waste (Yusuf et al 2015, 2016; Sanghvi et al 2016). The current application of proteases generally requires consideration of appropriate specificity and stability of pH, temperature, surfactants, and organic solvents (Sanghvi et al 2016). The search for proteases with higher enzyme activity and milder conditions is urgently needed for industrial applications
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