Isolation, identification and some cultural conditions of a protease-producing thermophilic Streptomyces strain grown on chicken feather as a substrate

Six strains of thermophilic actinomycetes were isolated from soil using an enrichment technique with feathers as the sole carbon and nitrogen source. They showed clear proteolytic activity on casein-agar medium. The most active strain was tentatively identified as Streptomyces thermonitrificans. This isolate was grown in a basal medium with feathers and/or other carbon and nitrogen sources. Supernatant from centrifuged cultures was examined for protease activity and temperature and pH optima were determined for enzyme activity. Optimum proteolytic activity on basal liquid medium containing 1% chicken feather pieces was obtained at 50 degrees C. in a medium adjusted at pH 8 and incubated for 72 h at 150 rpm. Proteolytic activity was further increased by 1.5% feather pieces and the time required for maximal activity was 96 h. The keratinolytic activity of S. thermonitrificans was examined by incubation with native chicken feather pieces and it was found that it is significantly active. The degradation of whole intact feathers by S. thermonitrificans was obtained after 48 h of incubation at 50 degrees C. The pH and temperature optima for proteolytic activity were 9.0 and 50 degrees C, respectively. The proteolytic activity was stable at 40 degrees C for I h. The proteolytic activity was inhibited by DFP but not by EDTA or pCMB. These results inidicated that the enzyme(s) can be classified as an alkaline protease. (C) 1999 Elsevier Science Ltd. All rights reserved.