A native-feather-degrading thermophilic anaerobe was isolated from a geothermal hot stream in Indonesia. Isolate AW-1, identified as a member of the species Fervidobacterium islandicum, was shown to degrade native feathers (0.8%, w/v) completely at 70°C and pH 7 with a maximum specific growth rate (0.14 h-1) in Thermotoga-Fervidobacterium (TF) medium. After 24 h of culture, feather degradation led to an increase in free amino acids such as histidine, cysteine and lysine. Moreover, nutritionally essential amino acids such as tryptophan and methionine, which are rare in feather keratin, were also produced as microbial metabolites. A homomultimeric membrane-bound keratinolytic protease (>200 kDa; 97 kDa subunits) was purified from a cell extract of F. islandicum AW-1. The enzyme exhibited activity toward casein and soluble keratin optimally at 100°C and pH 9, and had a half-life of 90 min at 100°C. The enzyme showed higher specific activity for the keratinous substrates than other proteases and catalyzed the cleavage of peptide bonds more rapidly following the reduction of disulfide bridges in feather keratin by 10 mM dithiothreitol. Therefore, the enzyme from F. islandicum AW-1 is a novel, thermostable keratinolytic serine protease.
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Acknowledgements This work (1999–0104) was supported by the Korea Science and Engineering Foundation (KOSEF). Technical support by Prof. G. Antranikian and H. Märkl (Technical University of Hamburg-Harburg, Germany) is greatly appreciated. We thank H. Hippe (DSMZ, Germany) for DNA-DNA hybridization and final characterization of F. islandicum AW-1.
All Science Journal Classification (ASJC) codes
- Molecular Biology