**3. Keratinases from microorganism**

The keratinase producing micro-organisms have been discovered in several different biological groups, including fungi, bacteria and actinomycetes**.**

#### **3.1 Bacterial strains**

*Advances in Poultry Nutrition Research*

feather meal.

**2. Keratin**

degradation rate.

complex architecture [16].

**2.1 Chicken feathers**

feathers were utilized as nitrogenous fertilizers due to their high value protein content [6, 7]. This feature of keratin protein can accomplish the shortage of meat raw materials and achieve desire of manufacturer to reduce production costs, and the availability of alternative sources of protein [8]. Feather degradation by microbial action seems to be a reasonable substitute to obtain feather meal that would be nutritionally raised with essential amino-acids. This line of biodegradation of chicken feathers would convert the rigid feather waste to a readily digestible

Keratin is hardened fiber plus matrix material which ultimately fills the cells of hair cortex. It thus consists of two main components; a fibrous protein which gives the α-keratin x-ray diffraction pattern (or the β-pattern when the polypeptide chains are extended as in feather keratin) and an amorphous protein which is termed γ-keratin [9]. Only rare microorganisms like fungi, bacteria and actinomycetes are capable to break and utilize keratin because of their hard and tough nature. Humans and other vertebrates cannot digest this macromolecule, and if eaten, it simply gets accumulated within the variety of a lump that is still undigested. A large part of tiger scat and other carnivore dung contains scleroprotein (mainly hair) aside from bones and additional complex elements which are undigestible [10]. Animal hair, hoofs, horns and wool contain β-keratin and bird's feather contains α-keratin. Keratins are also present in epithelial covering which is rich in beta helical coil linked through cysteine bridges [11]. The higher the percentage of sulfur, the higher is the stability of keratin towards solubilization [12]. The keratin proteins are compound that are extremely resistant to action of physical, chemical and biological agents. Hair, horns, nails and cornified tissue are some naturally occurring forms of keratin [13–14]. Keratin is a protein macromolecule with very high stability and low

Keratins are categorized into hard and soft keratins according to the sulfur content. Hard keratins have high content di-sulphide linking and are found in appendages. Soft keratins have low content of disulphide bond making skin and callus [15]. Keratins belong to the super family of IF protein. Intermediate filament

The main component of feather is keratin, a mechanically durable and chemically unreactive and insoluble protein, which render it difficult to be digested by most proteolytic enzymes. Keratin is resistant to enzymatic digestion by plant, animals and many known microbial proteases due to insoluble nature. Feathers having only 10% parts which is not keratin, rest 90% is resistant to degradation by common peptidases. This resistance is due to constituent amino acid composition and configuration that provide structural rigidity [17]. Chicken feathers are made up of over 90% of keratin protein, small amounts of lipids and water. Feathers contain about 15% N on a dry weight basis and huge quantities are produced as industrial by product. However, they have not been used effectively as plant bio

proteins are planned, prolonged α-helical conformation prone to form twostranded coiled coils. The durability of keratins is a direct consequence of their

**34**

The genera *Burkholderia*, *Chryseobacterium, Pseudomonas* and *Microbacterium* sp. were grown on solid medium with feather meal as sole carbon and chemical elements and screened for proteolytic activity on milk agar plates [19]. Three *Bacillus* species were isolated from the poultry industry and evaluated for keratinase production using feathers or feather meal as the sole carbon and nitrogen sources in a submerged fermentation. *B. subtilis* 1273 was the strain which exhibited the highest enzymatic activity [17]. A number of keratinases producing *Bacillus* and *Pseudomonas* species have been isolated from various environmental sources such as soil farm wastes and raw feather [20]. *Bacillus* sp., *Bacillus licheniformis*, *Bacillus subtilis* KD-N2, *Burkholderia* was isolated for keratinase production [21–22].

#### **3.2 Actinomycetes strains**

Thiosulfate production from cystine by keratinolytic prokaryote *Streptomyces fradiae* [23]. Biochemical mechanism of keratin degradation by the actinomycete *Streptomyces fradiae* and the fungus *Microsporum gypseum*: a comparison [24]. Keratinolytic serine protease was purified and characterized from *Streptomyces albidoflavus* [25]. Native keratin decomposition by thermophilic *Actinomycetes* was studied [26]. Keratinase enzyme was isolated and characterized, which was produced during wool degradation process by *Thermoactinomycetes candidus* [27]. Thermoactinomycetes degraded keratin and other collagenous waste by alkaline hydrolysis [28]. A new strain of *streptomyces* was used to degrade feather [29]. A new actinomycetes was isolated from coastal region of south India and studied keratinase production [30].

#### **3.3 Fungal strains**

The thermophiles may be advantageous in comparison with mesophiles, because of their accelerated reaction processes and the accumulation of biomass and enzymes and diminished the risk of contamination in industrial activity. A large number of keratinases producing fungi were observed by [31]. 234 fungal strains were isolated by baiting method used for feather degradation and keratinase producing ability. Maximum clearing zone was made by *Chrysosporium indicum* on solid agar plates. The highest keratinase production was found in case of *Acremonium strictum* while *Chrysosporium indicum* and *Chrysosporium tropicum* was found next to it [32]. Fungal keratinase reported from India are listed in **Table 1**.


#### **Table 1.**

*Fungal species producting keratinse.*
