Keratinases are proteases that, among other molecules, degrade robust keratin substrates. Most of them belong to extracellular serine proteases or metalloproteases. A number of fungi and bacteria produces them. Bacillus subtilis and Bacillus lichenformis are two of the most investigated producers, but they are also often isolated from actinomycetes. Methods of biotechnological production are different for every microorganism. Submerged cultivation is most frequently used, with a keratin substrate as the main source of carbon and nitrogen. Often, various sources of carbon, nitrogen and metal ions that act stimulative are added to the medium for optimization of production. Most keratinases are alkaline or neutral proteases, with a temperature optimum between 40-70°C. Many strains with a wide pH and thermostability range were isolated, which makes them applicable in many industries. In recent years, new possibilities for their use have been discovered. There is a great interest in their use in the field of degradation of waste from the agricultural and leather industry, biogas production, prion degradation, textile processing, medicines delivery, cosmetics, ... Biotechnological procedures using microbial keratinases can in many ways contribute to reduced organic waste accumulation in the environment and the production of recycled products with added value.
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