الفهرس 
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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.