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A mixed culture containing two recombinant Bacillus subtilis strains; was used to hydrolyze 1% chicken feather; both were previously transformed with late-expressed and early expressed alkaline protease (aprE) carrying plasmids pS1 and p5.2, respectively. Proteolytic and keratinolytic activities of the mixed culture increased in parallel with those of the culture of B. subtilis DB100 (p5.2), and both were higher than that of B. subtilis (pS1) cultures. On the other hand, data indicated that degradation of feather by the recombinant strains B. subtilis DB100 (p5.2), was greatly enhanced when using a previously optimized medium. High levels of free amino groups as well as soluble proteins were also obtained. The concentration of amino acids was considerably increased during the fermentation process. It was found that, the amino acids Phe, Gly and Tyr were the major amino acids liberated in the cultures initiated by both strains. Results render these recombinant strains suitable for application in feather biodegradation large scale processes. [ABSTRACT FROM AUTHOR]