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Abstract Keratinous wastes are increasingly accumulating in the environment mainly in the form of feathers, hair and wool generated from various sources. Today, they are also becoming a part of solid waste management and wastage of a protein rich reserve because they are tough to degrade by common proteolytic enzymes (1-5). Keratin, an insoluble animal protein, represents about 90% of these keratinous wastes (6,7). The complexity in keratin structure is due to high cross linking between the polY8eptide chains as a result of S-S bonds, hydrogen bonds and hyDROPhobic interactions 2, 5, 8, 9). Accumulation of abundant amounts of these wastes along with inefficient utilization imposes several environmental health hazards (10 - 12). On the other hand, researchers interested in animal feedstuffs allover the world have paid a lot of attention to these keratinous wastes due to their high protein content (\3, 14). However, the high recalcitrant nature of these wastes greatly hinders their utilization in the native state as animal feedstuffs unless it had been undergone physicochemical treatments. Currently, the production of commercial feather meals demands the use of these physicochemical methods. However, the resulting product has a low nutritional value and is poor in some essential amino acids such as methionine and histidine. Additionally, high cost and intensive energy are two prerequisites for the completion of the process. The aforementioned shortcomings of these physicochemical methods’ addressed the urgent need for other biotechnological alternatives (4,15 - 18). Despite the recalcitrant nature, keratinous wastes can be efficiently degraded by a variety of bacteria, actinomycetes and fungi due to the elaboration of keratinolytic proteases’l”. Isolation and purification of several keratinolytic enzymes from keratinolytic microorganisms have been reported (4, 5, 20 - 25). The potential role of these keratinolytic enzymes (mostly serine proteases and lesser metalloproteases) towards biotechnological valorization of keratinous wastes has been described (2, 19,26 - 28). As a consequence of the keratinases importance, some reports highlighted certain trails to clone and express genes encoding for keratinolytic enzymes in a variety of expression systems (such as Bacillus subtilis, E. coli and Pichia pas/oris) (29, 30). The keratinolytic alkaline protease aprE gene from B. subtilis cells has been cloned and expressed in two successive pUBllO based vectors namely (pSI) and (pS.2) (31 - 33). The biodegradation of keratin in the form of chicken feather directed by B. subtilis DB 100 (pSI) and B. subtilis DB 100 (pS.2) recombinant cells was accompanied with the production of considerable levels of alkaline protease, soluble proteins and NHrfree amino groups (34, 35). However, these previous studies did not handle optimization of feather biodegradation process by these recombinant strains. Moreover, all feather biodegradation experiments directed by the above two B. subtilis recombinant strains were carried out on a flask scale only. Additionally, data concerning the possibility of biodegrading raw sheep wool; another abundant keratinous waste; through the above two recombinant strains were not available. The present work aims to optimize the biodegradation of two keratinous wastes namely, chicken feathers and raw sheep wool through recombinant Bacillus strains. As a matter of fact, process optimization is a topic of central importance in the agenda of any fermentation process, in which even small improvements can be decisive for commercial success. The optimization strategy applied in the present work involves two steps. |