## 1 Introduction  
Keratinase (EC3.4.21/24/99.11) is a class of enzymes that can specifically degrade keratin, which is a structural protein used by animals for mechanical protection with sulfur-containing compounds and disulfide bonds. It can degrade feathers and other difficult-to-degrade keratinous substances with low energy consumption and environmental friendliness, which has application potential in husbandry [1; 2], medical [3; 4; 5], cosmetics, biological materials [6] and other industries. Keratin is widely found in agricultural waste, especially bird feathers from poultry processing plants [7], and urgently needs to be processed and recycled. In the process of feather degradation, higher temperatures are favorable for the destruction of disulfide bonds in keratin, which improves hydrolysis efficiency. However, high temperature will destroy the non-covalent interaction of proteins and eventually lead to enzyme inactivation. Keratinolytic thermophilic or hyperthermophilic bacteria and archaea have been known to degrade keratin at \(\geq\)70 \({}^{\circ}\)C [8]. At present, many keratinases have been identified from microorganisms, but the number of keratinases used in the market is very small, which might be related to the thermal stability of keratinases [9]. Therefore, it is very important to find and identify high temperature-adaptive keratinases.  
In order to find thermally stable keratatinases, researchers tend to isolate keratinase bacteria from a high-temperature environment, such as hyperthermophilic archaeon _Thermococcus kodakaranensis_[10], the thermophile strain _Meiothermus taiwanensis_ WR-220 (isolatedfrom hot springs) [11], etc. The optimal temperature and pH of keratinase MtaKer from _M. taiwanensis_ WR-220 are 65 \({}^{\circ}\)C and pH 10, respectively. MtaKer has keratinase activity in a larger temperature and pH range. In extreme environments, the protein encoded by extremophiles should evolve into functional proteins to adapt to the environment. The strong tolerance of Mtaker may be related to the extreme living environment of _M. taiwanensis_ WR-Many recent studies have focused on extremozymes, especially the high temperature-resistant enzymes, because adjustment to industrial harsh conditions needs the activity and stability of the applied enzymes in such conditions [12; 13]. Since evolution and natural selection have occurred in the environment for billions of years, extreme bacteria may produce customized enzymes with some unique properties required for industrial applications. _Deinococcus_ bacteria are famous for their radiation tolerance, however, the peptidase genes present in their genome are ignored. _D. geothermalis_ was discovered in hot springs, and the optimal growth temperature of _D. geothermalis_ is 50 \({}^{\circ}\)C, higher than the growth temperature of medium-temperature bacteria. The enzymes of _D. geothermalis_ might have good tolerance to extreme industrial conditions, especially thermostability.  
In this study, the keratinase gene _Dgeo_0978_, named _degKer_, was identified from the _D. geothermalis_ genome. The keratinase DgeKer (GenBank N. WP_011530115.1) from _D. geothermalis_ was successfully expressed and purification in _E. coli_ BL21-codonplus (DE3) strains. The biochemical properties of the recombinant enzyme and the ability in degrading feathers were examined. The results showed that DgeKer had high activity under high temperature and pH conditions, which making it a promising enzyme for industry.