Production of keratinase by Bacillus subtilis S14

High keratinase and other types of hydrolase activity of the new strain of Bacillus paralicheniformis

Keratinases, a subclass of proteases, are used to degrade keratin thereby forming peptones and free amino acids. Bacillus paralicheniformis strain T7 was isolated from soil and exhibited high keratinase, protease, collagenase, amylase, xylanase, lipase, and phosphatase activities. Keratinases of the strain showed maximum activity at 70°C and pH 9.0 as well as high thermal stability. A mass-spectrometric analysis identified seven peptidases with molecular masses of 26.8-154.8 kDa in the secretory proteome. These peptidases are members of S8 and S41 serine peptidase families and of M14, M42, and M55 metallopeptidase families. Additionally, α-amylase (55.2 kDa), alkaline phosphatase (59.8 kDa), and esterase (26.8 kDa) were detected. The strong keratinolytic properties of the strain were confirmed by degradation of chicken and goose feathers, which got completely hydrolyzed within 4 days. Submerged fermentation by strain B. paralicheniformis T7 was carried out in a pilot bioreactor, where the highest keratinase production was noted after 19 h of cultivation. After the fermentation, in the culture fluid, the keratinase activity toward keratin azure was 63.6 ± 5.8 U/mL. The protease activity against azocasein was 715.7 ± 40.2 U/mL. The possibility of obtaining enzyme preparations in liquid and powder form was demonstrated, and their comparative characteristics are given. In the concentrate, the keratinase, protease, α-amylase, phosphatase, and esterase/lipase activities were 2,656.7 ± 170.4, 29,886.7 ± 642.9, 176.1 ± 16.3, 23.9 ± 1.8, and 510.9 ± 12.2 U/mL, respectively. In the lyophilizate, these activities were 57,733.3 ± 8,911.4, 567,066.7 ± 4,822.2, 2,823.0 ± 266.8, 364.2 ± 74.8, and 17,618.0 ± 610.3 U/g, respectively. In the preparation obtained by air flow drying at 55°C, these activities were 53,466.7 ± 757.2, 585,333.3 ± 4,277.1, 2,395.8 ± 893.7, 416.7 ± 52.4, and 15,328.1 ± 528.6 U/g, respectively. The results show high potential of B. paralicheniformis strain T7 as a producer of keratinases and other enzymes for applications in agricultural raw materials and technologies for processing of keratin-containing animal waste.

Valorization of chick feather wastes by Geobacillus thermodenitrificans PS41 to enhance the growth of Vigna unguiculata plant and Cyprinus carpio fish

Chicken feather meal has had a significant biofertilizer approach in recent years. The current study aims to assess feather biodegradation to promote plant and fish growth. The Geobacillus thermodenitrificans PS41 strain was more efficient in feather degradation. Feather residues were separated after degradation and evaluated under a scanning electron microscope (SEM) to detect bacterial colonization on feather degradation. It was observed that the rachi and barbules were entirely degraded. The complete degradation by PS41 suggests a relatively more efficient feather degradation strain. According to Fourier-transform infrared spectroscopy (FT-IR) studies, PS41 biodegraded feathers contain the functional groups of aromatic, amine, and nitro compounds. The present study suggested that biologically degraded feather meal improved plant growth. The feather meal combined with nitrogen-fixing bacterial strain showed the highest efficiency. The biologically degraded feather meal and Rhizobium combination induced physical and chemical changes in the soil. It is directly involved in soil amelioration, plant growth substance, and soil fertility, enhancing a healthy crop environment. The feather meal 4 and 5% was used as a feed diet of common carp (Cyprinus carpio) to increase growth performances and feed utilization parameters. In hematological and histological studies of formulated diets, significantly no toxic effects occurred in fish blood, gut, or fimbriae.

Enhanced keratinase production by Bacillus subtilis amr using experimental optimization tools to obtain feather protein lysate for industrial applications

The poultry industry produces millions of tons of feathers waste that can be transformed into valuable products through bioprocess. The study describes the enhanced keratinase and feather hydrolysate production by Bacillus subtilis AMR. The metabolism of each microorganism is unique, so optimization tools are essential to determine the best fermentation parameters to obtain the best process performance. The evaluation of different propagation media indicated the constitutive production of two keratinases of approximately 80 kDa. The combination of Mn²⁺, Ca²⁺, and Mg²⁺ at 0.5 mM improved the keratinolytic activity and feather degradation 1.5-fold, while Cu²⁺ inhibited the enzymatic activity completely. Replace yeast extract for sucrose increased the feather hydrolysate production three times. The best feather concentration for hydrolysate production was 1.5% with an inoculum of 10⁸ CFU/mL and incubation at 30 °C. None of the inorganic additional nitrogen sources tested increased hydrolysate production, although (NH₄)₂SO₄ and KNO₃ improved enzymatic activity. The optimization process improved keratinolytic activity from 205.4 to 418.7 U/mL, the protein concentration reached 10.1 mg/mL from an initial concentration of 3.9 mg/mL, and the feather degradation improved from 70 to 96%. This study characterized keratinase and feather hydrolysate production conditions offering valuable information for exploring and utilizing AMR keratinolytic strain for feather valorization.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03153-y.

Microbial enzymes catalyzing keratin degradation: Classification, structure, function

Keratin is an insoluble and protein-rich epidermal material found in e.g. feather, wool, hair. It is produced in substantial amounts as co-product from poultry processing plants and pig slaughterhouses. Keratin is packed by disulfide bonds and hydrogen bonds. Based on the secondary structure, keratin can be classified into α-keratin and β-keratin. Keratinases (EC 3.4.-.- peptide hydrolases) have major potential to degrade keratin for sustainable recycling of the protein and amino acids. Currently, the known keratinolytic enzymes belong to at least 14 different protease families: S1, S8, S9, S10, S16, M3, M4, M14, M16, M28, M32, M36, M38, M55 (MEROPS database). The various keratinolytic enzymes act via endo-attack (proteases in families S1, S8, S16, M4, M16, M36), exo-attack (proteases in families S9, S10, M14, M28, M38, M55) or by action only on oligopeptides (proteases in families M3, M32), respectively. Other enzymes, particularly disulfide reductases, also play a key role in keratin degradation as they catalyze the breakage of disulfide bonds for better keratinase catalysis. This review aims to contribute an overview of keratin biomass as an enzyme substrate and a systematic analysis of currently sequenced keratinolytic enzymes and their classification and reaction mechanisms. We also summarize and discuss keratinase assays, available keratinase structures and finally examine the available data on uses of keratinases in practical biorefinery protein upcycling applications.

Response Surface Methodology for the Optimization of Keratinase Production in Culture Medium Containing Feathers by Bacillus sp. UPM-AAG1

Keratinase is a type of proteolytic enzyme with broad application in industry. The main objective of this work is the optimization of keratinase production from Bacillus sp. strain UPM-AAG1 using Plackett-Burman (PB) and central composite design (CCD) for parameters, such as pH, temperature, feather concentration, and inoculum size. The optimum points for temperature, pH, and inoculum and feather concentrations were 31.66 °C, 6.87, 5.01 (w/v), and 4.53 (w/v), respectively, with an optimum keratinase activity of 60.55 U/mL. The keratinase activity was further numerically optimized for commercial application. The best numerical solution recommended a pH of 5.84, temperature of 25 °C, inoculums’ size of 5.0 (v/v), feather concentration of 4.97 (w/v). Optimization resulted an activity of 56.218 U/mL with the desirability value of 0.968. Amino acid analysis profile revealed the presence of essential and non-essential amino acids. These properties make Bacillus sp. UPM-AAG1 a potential bacterium to be used locally for the production of keratinase from feather waste.

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.

The host range of dermatophytes, it is at all possible? Phenotypic evaluation of the keratinolytic activity of Trichophyton verrucosum clinical isolates

Dermatophytes are fungi that have an ability to invade keratinised structures. Enzymes secreted by dermatophytes can underlie fungal survival on the host and development of infection. It is possible that the range of activity of keratinases from various dermatophytes is limited to specific species of animals and groups of people. The aim of this study was to carry out phenotypic analysis of the degree of keratinolytic activity of Trichophyton verrucosum strains using hairs of humans and various animal species as substrates. Our results indicated that the activity of keratinases is substrate-induced. The host range of T. verrucosum can be defined as wide. The highest activity of keratinases was recorded in media containing keratin from cow (Bos taurus) and sheep (Ovis aries) hairs in comparison with that from other tested species. The production of keratin-degrading enzymes is a function of time, with the peak of their activity occurring on day 15 of incubation. The role of keratin-degrading enzymes in the pathogenesis of dermatophytosis is becoming increasingly clearer. Given the conceptual understanding that keratin breakdown may require more than just one enzyme, the use of phenotypic methods is an optimal approach to in vitro study of the decomposition of species-specific keratin.

Discovery of Two Chrysosporium Species with Keratinolytic Activity from Field Soil in Korea

In an ongoing survey of Korean indigenous fungi, two fungal strains (KNU16-74 and KNU16-99) belonging to the genus Chrysosporium were isolated from field soil in Gyeongnam, Korea. Morphological characterization and phylogenetic analysis using sequence of the internal transcribed spacer regions were carried out to confirm its precise identification. These strains were identified as Chrysosporium indicum (KNU16-74) and Chrysosporium fluviale (KNU16-99). To examine the keratin degradation efficiency of these two fungal species, human hair strands were incubated with fungus culture. Results revealed that these two fungal species have the ability to degrade keratin substrate. This is the first report of these two species in Korea.

New keratinolytic bacteria in valorization of chicken feather waste

There is an increasing demand for cost-effective and ecologically-friendly methods for valorization of poultry feather waste, in which keratinolytic bacteria present a great potential. Feather-degrading bacteria were isolated from living poultry and a single strain, identified as Kocuria rhizophila p3-3, exhibited significant keratinolytic properties. The bacterial strain effectively degraded up to 52% of chicken feathers during 4 days of culture at 25 °C. Zymographic analysis revealed the presence of two dominating proteolytic enzymes in the culture fluid. Culture conditions were optimized in order to maximize the liberation of soluble proteins and free amino acids. A two-step procedure was used, comprising a Plackett-Burman screening design, followed by a Box-Behnken design. Concentration of feather substrate, MgSO₄ and KH₂PO₄ were the most influential parameters for the accumulation of soluble proteins in culture K. rhizophila p3-3, while feathers and MgSO₄ also affected the concentration of amino acids. The resultant raw hydrolysate supernatant, prior to and after additional treatments, was rich in phenylalanine, histidine, arginine and aspartic acid. Additionally the hydrolysate exhibited radical-scavenging activity and ferric reducing power.

Purification and partial characterization of serine-metallokeratinase from a newly isolated Bacillus pumilus NRC21

A serine metallokeratinase enzyme (30 kDa) produced by a newly isolated Bacillus strain (Bacillus pumilus NRC21) cultivated under optimized conditions in medium containing chicken feather meal was purified and characterized in a set of biochemical assays. The purification was carried out using two successive chromatographic steps; cation exchange chromatography on CM-cellulose and gel filtration on sephadex G-100 columns. The purified enzyme showed a specific activity of 2000 units/mg protein against 170 units/mg protein for crude extract with 12 fold purification. The enzymatic activity of the keratinase stimulated by (Na(+), K(+), Mg(2+)), Hg(+2) had no effect, and inhibited by entire tested cations, serine and metalloproteinase inhibitors, therefore it can be considered as a serine metalloenzyme. The optimum pH and temperature for the purified enzyme were (7.5, 8.5) and (50, 45 °C) when using keratin azure and azocasein as substrates, respectively. The purified enzyme was highly stable at broad pH and temperature ranged (5-10) and (20-60 °C), respectively and its thermoactivity and thermostability were enhanced in the presence of 5 mM Mg(+2). These results suggest that the purified keratinase may be used in several industrial applications.