Keratinase production by Bacillus pumilus GHD in solid-state fermentation using sugar cane bagasse: optimisation of culture conditions using a Box-Behnken experimental design

Bioconversion of agro-food industrial wastes into value-added peptides by a Bacillus sp. Mutant through solid-state fermentation

Advances in microbial enzyme technology offer a significant opportunity for developing low-energy bioconversion solutions for industrial wastes as inexpensive feedstocks for useful products. In this short communication, two agro-food industrial wastes, chicken feather powder (CFP) and okara, were converted into peptides by a Bacillus licheniformis mutant using solid-state fermentation (SSF). The optimum SSF conditions for okara to CFP ratio, inoculum size, and time were 0.7 (7:10), 15%, and 90 h, respectively, which produced 185.99 mg/g peptides, with 910.12 U/g keratinase activity and 85.03% antioxidant scavenging activity. Compared to okara, CFP with mutant strain showed 11.28% higher keratinase activity and produced higher amounts of peptides (5.51%).

Structure, Application, and Biochemistry of Microbial Keratinases

Keratinases belong to a class of proteases that are able to degrade keratins into amino acids. Microbial keratinases play important roles in turning keratin-containing wastes into value-added products by participating in the degradation of keratin. Keratin is found in human and animal hard tissues, and its complicated structures make it resistant to degradation by common proteases. Although breaking disulfide bonds are involved in keratin degradation, keratinase is responsible for the cleavage of peptides, making it attractive in pharmaceutical and feather industries. Keratinase can serve as an important tool to convert keratin-rich wastes such as feathers from poultry industry into diverse products applicable to many fields. Despite of some progress made in isolating keratinase-producing microorganisms, structural studies of keratinases, and biochemical characterization of these enzymes, effort is still required to expand the biotechnological application of keratinase in diverse fields by identifying more keratinases, understanding the mechanism of action and constructing more active enzymes through molecular biology and protein engineering. Herein, this review covers structures, applications, biochemistry of microbial keratinases, and strategies to improve its efficiency in keratin degradation.

Molecular strategies to increase keratinase production in heterologous expression systems for industrial applications

Keratinase is an important enzyme that can degrade recalcitrant keratinous wastes to form beneficial recyclable keratin hydrolysates. Keratinase is not only important as an alternative to reduce environmental pollution caused by chemical treatments of keratinous wastes, but it also has industrial significance. Currently, the bioproduction of keratinase from native keratinolytic host is considered low, and this hampers large-scale usage of the enzyme. Straightforward approaches of cloning and expression of recombinant keratinases from native keratinolytic host are employed to elevate the amount of keratinase produced. However, this is still insufficient to compensate for the lack of its large-scale production to meet the industrial demands. Hence, this review aimed to highlight the various sources of keratinase and the strategies to increase its production in native keratinolytic hosts. Molecular strategies to increase the production of recombinant keratinase such as plasmid selection, promoter engineering, chromosomal integration, signal peptide and propeptide engineering, codon optimization, and glycoengineering were also described. These mentioned strategies have been utilized in heterologous expression hosts, namely, Escherichia coli, Bacillus sp., and Pichia pastoris, as they are most widely used for the heterologous propagations of keratinases to further intensify the production of recombinant keratinases adapted to better suit the large-scale demand for them. KEY POINTS: • Molecular strategies to enhance keratinase production in heterologous hosts. • Construction of a prominent keratinolytic host from a native strain. • Patent analysis of keratinase production shows rapid high interest in molecular field.

Comprehensive insights into microbial keratinases and their implication in various biotechnological and industrial sectors: A review

Enormous masses of keratinous wastes are annually accumulated in the environment as byproducts of poultry processing and agricultural wastes. Keratin is a recalcitrant fibrous protein, which represents the major constituent of various keratin-rich wastes, which released into the environment in the form of feathers, hair, wool, bristle, and hooves. Chemical treatment methods of these wastes resulted in developing many hazardous gases and toxins to the public health, in addition to the destruction of several amino acids. Accordingly, microbial keratinases have been drawing much interest as an eco-friendly approach to convert keratinous wastes into valuable products. Numerous keratinolytic microorganisms have been identified, which revealed the competence to hydrolyze keratins into peptides and amino acids. Several types of keratinolytic proteases have been produced that possess diverse biochemical characteristics, conferring them the versatility for implementing in multifarious applications such as detergents, leather and textile industries, animal feeding, and production of bio-fertilizers, in addition to medical and pharmaceutical treatments. This review article emphasizes the significance of keratinases and keratinase based-products via comprehensive insights into the keratin structure, diversity of keratinolytic microorganisms, and mechanisms of keratin hydrolysis. Furthermore, we discuss the biochemical properties of the produced keratinases and their feasible applications in diverse disciplines.

Hydrolyzing proficiency of keratinases in feather degradation

The keratinase degrade highly rigid, cross linked structural polypeptides with different efficiency depending on the type of source. Two newly isolated strains of Bacillus subtilis (RSE163 and RSE165; NCBI Accession no JQ887983 and JQ887982) were found to be efficient keratinase producers with unusual catalytic activity result in different morphological changes in degradation pattern of feather, confirmed by their scanned electron micrographs. Maximum keratinolytic activity of both the strains B. subtilis RSE163 and RSE165 were found to be 366 ± 15.79 and 194 ± 7.26 U after 72 h of incubation. While the disulphide reductase activity of RSE163 and RSE165 estimated 0.24 ± 0.05 and 0.15 ± 0.03 U/ml of enzyme after 24 h of incubation. A total of 16 free amino acids of variable concentration were also analyzed in the cell free supernatant of hydrolyzed feather from two strains. Present study demonstrates the action of two different keratinases in feather degradation.