Annually, just the global feather waste from the poultry processing industry reaches 8.5 million tons. At present, the poultry feathers are dumped, buried, used for land filling, or incinerated, resulting in environmental challenges in terms of storage, handling, emission control, and ash disposal (Agrahari and Wadhwa 2010). Poultry feathers are also turned into feather meal used as animal feed because of the high protein content. However, the use of waste for animal feed is becoming tighter (Commission of the European Communities 2000). Additionally, the high treatment costs make the process economically unfeasible. An environmentally and economically promising process to recover the feather waste is to produce renewable energy by e.g. anaerobic digestion. In this process, not only does the valuable methane result as a byproduct, but also digested residues are formed. The latter can safely be used as a fertilizer, since pathogens presented in the feather waste have been eradicated in the process (Salminen and Rintala 2002a, b).
The recalcitrant keratin is the major compound in several biological materials. It is also the waste product in poultry, slaughterhouse, leather- and fur processing industries and consists of feather, hair, horn, hoof, nails, claws, wool, and bristles (Kornillowicz-Kowalska and Bohacs 2011). While some of the materials like hair or wool, to a great extent, are composed of the helix form of ?-keratin, other materials such as feather are largely composed of the flat form of ?-keratin. Among the two different types of keratin structures, the content of sulfur varies giving the keratin a softer or harder structure and affects the degradation of the keratinous material to a greater extent (Brandelli et al. 2010). A large number of microorganisms have been reported to produce keratinases (Brandelli et al. 2010; Gupta and Ramnani 2006; Onifade et al. 1998), and among bacteria, the best studied are organisms from the genus Bacillus (Gobinath et al. 2014). Keratinases (EC 3.4.99.11) are serine- or metalloproteases (Gupta and Ramnani 2006), and many bacterial keratinases have been sequenced, cloned, and characterized indicating a sequence similarity with the subtilisin family, Family S8, of serine proteases (Rawlings and Barret 1993).
The isolation and characterization of a keratin-degrading bacterium, Bacillus sp C4, has been reported by this lab. The proteolytic activity was broadly specific, and the bacterium could grow and produced a significant level of keratinase when using wool or chicken feather as substrates. A total hydrolysis of the keratinous waste was obtained in less than 3 days (Fellahi et al. 2014). Also this proteolytic enzyme has shown activity and stability over a broad pH range with two distinct optima, one at pH 8.5 and the other at pH 11, indicating that it might be not one but two enzymes. Its activity was completely inhibited by phenylmethylsulfonyl fluoride (PMSF) pointing out that the enzyme is a serine protease (Fellahi 2009).
In an attempt to increase our understanding of the Bacillus strain’s ability to simultaneously hydrolyze both ?- and ?-keratin, we in this study aimed to show the characteristics of the keratinolytic protease and to identify its gene. So far, the vast majority of the identified keratinase-producing organisms appears to be able to hydrolyze only the ?-keratin in the chicken feather (Gupta et al. 2013), which gives the keratinolytic protease from this strain a potential for simultaneous degradation of both types of keratin in waste refinery.