Industrial sustainability of microbial keratinases: production and potential applications

Abstract

Keratinases are proteolytic enzymes with a particular ability to cleave peptide bonds in keratin, and in other proteins. Due to their broad-spectrum of activity, keratinases are considered viable substitutes for chemical and thermal treatments of proteinrich industrial by-products. Among these protein residues, special attention has been given to keratinous materials (feathers, hair, horns, etc.), which disposal through harsh conditions methods, such as acid/alkaline hydrolysis or incineration, is not considered ecologically safe. Microbial keratinolytic enzymes allow for keratin degradation under mild conditions, resulting in keratin hydrolysates containing undamaged amino acids and peptides. In this review article, we offer perspectives on the relevance of these unique biocatalysts and their revolutionary ascent in industries that generate keratin-rich wastes. Additionally, we share insights for applications of keratinases and protein hydrolysates in agriculture, animal feed, cosmetics, phamaceuticals, detergent additives, leather processing, and others. Due to the scientific importance of keratinases and their potential use in green technologies, searching for bacterial and fungal species that efficiently produce these enzymes may contribute to the sustainability of industries.

Valorization of Livestock Keratin Waste: Application in Agricultural Fields

“…Since the cost of keratinase production is high, several researchers have increased the yield and stability of keratinases by altering the genome of keratinolytic organisms via physical and chemical mutagenesis or recombinant DNA technologies [ 80 , 82 , 90 , 93 , 94 , 95 , 96 ]. Keratinases have become increasingly popular, and many studies have reviewed their discovery, production, classification, structure, hydrolysis function, and industrial application [ 9 , 97 , 98 , 99 , 100 ]. Biological techniques are environmentally friendly methods to hydrolyze keratin, but they require more time than other methods.…”

Perspectives on Converting Keratin-Containing Wastes Into Biofertilizers for Sustainable Agriculture

“…Indeed, bacteria, actinomycetes, and fungi are shown to have the capability to degrade keratin (Calin et al, 2017 ; Bohacz and Korniłłowicz-Kowalska, 2019 ). Many researchers have isolated keratin-degrading microorganisms from different environments and proved that these microorganisms can be utilized to convert keratinous wastes into value-added products (de Menezes et al, 2021 ; Nnolim and Nwodo, 2021 ). These isolated microorganisms exhibited their potential to degrade keratin and keratin-containing wastes such as feathers into soluble fractions and amino acids (Callegaro et al, 2018 ; Shanmugasundaram et al, 2018 ; Bohacz, 2019 ; Tamreihao et al, 2019 ; Chaudhary et al, 2021 ).…”

Structure, Application, and Biochemistry of Microbial Keratinases

“…Interestingly, a study showed that glucose and ammonium nitrate are not good sources for growing Stenotrophomonas maltophilia to degrade feathers ( Qu et al, 2018 ). Accumulated studies suggest that different microorganisms require various fermentation conditions for large-scale production, indicating that careful exploratory studies are necessary prior to the large-scale production of the enzymes ( Jagadeesan et al, 2020 ; de Menezes et al, 2021 ; Deniz et al, 2021 ; Sharma and Kango, 2021 ). It was demonstrated that the solid-state fermentation increased keratinase production compared with the commonly used submerged fermentation ( Inácio et al, 2018 ).…”

“…As keratin does not accumulate in nature, microorganisms are playing the major role in its degradation and recycling. Therefore, keratinous wastes threatening the environment can be converted into value-added products by using microbial treatment ( de Menezes et al, 2021 ; Nnolim and Nwodo, 2021 ). Extensive studies have been carried out to search suitable microorganisms and obtain optimized processes to make full use of keratinous wastes ( Gradišar et al, 2000 ; Sangali and Brandelli, 2000 ; Kim et al, 2001 ; Rai and Mukherjee, 2011 ).…”

“…Keratin is also classified as hard keratin and soft keratin based on the content of cysteine ( Jin et al, 2017 ). As basic units of keratin are polypeptides, keratinases play a major role in keratin degradation by breaking the disulfide bonds and peptidic bonds ( Fraser and Parry, 2008 ; Hassan et al, 2020 ; de Menezes et al, 2021 ). One of the features of keratinases is that they are able to cleave a sequence with hydrophobic residues at the P1 position ( Brandelli et al, 2010 ).…”