Keratin Waste Recycling Based on Microbial Degradation

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Keratin Waste Recycling Based on Microbial Degradation: Mechanisms and Prospects Zheng Peng, Juan Zhang, Guocheng Du, and Jian Chen ACS Sustainable Chem. Eng., Just Accepted Manuscript • Publication Date (Web): 04 May 2019 Downloaded from http://pubs.acs.org on May 4, 2019

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ACS Sustainable Chemistry & Engineering

Keratin Waste Recycling Based on Microbial Degradation: Mechanisms and Prospects Zheng Penga,c, Juan Zhanga,c*, Guocheng Dua,c, Jian Chenb,c*

aKey

Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, Wuxi 214122

bNational

Engineering Laboratory for Cereal Fermentation Technology, Jiangnan University, Wuxi

214122, China cSchool

of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China

*Corresponding authors Address: School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China. Tel.: +86 510 85918307; fax: +86 510 85918309. E-mail addresses: [email protected] (J. Zhang), [email protected] (J. Chen)

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Abstract The severe shortage of protein resources has motivated researchers to seek cheap and sustainable proteins and to produce new functional materials in an environmentally friendly way. Keratin is a ubiquitous and stubborn protein that is attractive for sustainability but difficult to recycle. Structurally, keratin is characterized by a large amount of disulfide bonds, hydrogen bonds and hydrophobic forces and results in considerable hardness. Bio-recycling of keratin is more promising than traditional processors because of the green production process, rich products and higher product value. Microbial strains capable of degrading keratin are constantly being developed. However, the mechanism of keratin decomposition by these microorganisms is not fully elucidated, which greatly hinders the sustainable use of keratin waste. In this review, we summarize the underlying mechanisms involved in microbial decomposition of keratin and attempt to discuss prospects and future directions in conjunction with systems biology strategies. Key words: Keratin; microbial decomposition; mechanisms; disulfide bond opening; keratinase; sustainability

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Introduction The global population surge has led to an increasing demand for protein, and the current protein resources are already quite tight. In addition, with the large consumption of poultry meat products, millions of tons of keratin waste are produced each year, which not only wastes protein resources but also causes serious environmental problems 1. Keratin is a major structural protein that forms the epidermal and epidermal appendages of vertebrates, which originate from ectoderm cells 2, 3, and composes hair, scales, feathers, nails, hoofs, horns, claws, jaws, silk, and other epidermal structures 4. Keratin is fibrous and an important member of the intermediate filament family; it is also known as the third most difficult polymer to degrade in the natural world after cellulose and chitin 5-7. The intractability of keratin and its resistance to common proteases primarily stems from the tightly packed polypeptide chain structures formed by the cross-linking of α-helices (α-keratin, 40–68 kDa) and β-sheets (β-keratin, 10–22 kDa) through a large number of disulfide bonds and hydrophobic interaction forces 8, 9. The number of disulfide bonds is the decisive factor in the hardness of keratin, which also leads to differences in their resistance to chemical substances and enzymes 10. Keratins of different hardness exhibit differences in cysteine content. Hair and wool (10-17% cysteine content) are typically hard keratins, as are feathers (4-8% cysteine content), and skin is soft keratin (2% cysteine content) 11-13. Methods that have been developed for keratin hydrolysis primarily include physical (pressurized hydrolysis, puffing, and microwaving) or chemical (acid and alkali) 14, 15. However, these methods present limitations, such as high energy consumption during the production process and high levels of damage to the reaction products 16. On the other hand, microbial degradation of keratin has advantages of being environmentally friendly and the ability of producing high-value products—albeit 3



at suboptimal efficiency 17. Microorganisms with keratin decomposition ability are mainly bacteria, fungi and actinomycetes, and most of them are isolated from feathers and soil of decayed keratin waste heaps 18. Dermatophytes, such as Trichophyton rubrum, Scopulariopsis brevicaulis, Microsporum gypseum, etc, were the first microorganisms found to degrade keratin 19-24. Bacteria are the major players in keratin decomposition and are also the most studied. Among them, Bacillus spp., such as Bacillus licheniformis, Bacillus subtilis, Bacillus amyloliquefaciens, etc have emerged as prominent keratinase producers 25-28. Other bacterial species include Stenotrophomonas maltophilia 29,

and Pseudomonas aeruginosa 30. In addition, Streptomyces spp. are the main actinomycetes with

keratin degradation activity 31-35. Although these strains possess the ability to degrade keratin, it is basically impossible to recover keratin waste owing to the inefficiency of wild-type bacterial decomposition or enzymatic hydrolysis of related wild-type enzymes. Therefore, engineering more efficient strains is imperative and the mechanism by which microbes degrade keratin is essential to understand for establishing microbial cell factories. Microbial degradation products of natural keratin are considered a huge library of protein resources, but we lack sufficient theory to support their further development. There are currently no reviews on the mechanisms by which microorganisms degrade keratin. Thus, the purpose of this review is to discuss possible mechanisms underlying the various stages of keratin microbial degradation and to analyze their potential in establishing microbial cell factories. We also provide strategies that combine systems and synthetic biology into an effective tool for improving the production and productivity of keratin recycling in the future.

Denaturation: Breaking disulfide bonds Concurrent with microorganism growth and metabolism, keratin is gradually degraded and 4


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eventually converted into small molecules (amino acids and peptides) and energy 36, 37. This process involves three essential steps of denaturation, decomposition, and transamination 38. Denaturation and decomposition considered to be the key to microbial degradation of keratin. In the following sections we will focus on the current research and further direction of these two processes. Keratin is unusually hard because it contains a large number of disulfide bonds 39. Therefore, the first step is to destroy these disulfide bonds to loosen the structure. Current research on the mechanisms of disulfide bond destruction can be summarized into four types, the biomembrane potential 40, mechanical pressure 41, thiolysis 42, and enzymatic hydrolysis theories 43. Biomembrane potential theory Biomembrane potential depends on the cell-bound redox reaction system of the cell membrane surface or soluble reducing substances secreted out of the cell, which is a theory based on the existence of whole cells with metabolic activity. Bockle 44 investigated where disulfide bond breakage occurs during feather degradation by Streptomyces pactum by separating this degradation system into several parts. As a result, it was found that washed mycelia had the greatest reducing power for disulfide bonds while fresh culture filtrate had a weak reducing power. On the other hand, cell homogenates had no reducing power regardless of NADH or NADPH addition. This indicates that the redox system on the cell surface or the reducing agent secreted to the outside of the cell can break disulfide bonds and promote keratin degradation. Ramnani et al. found that neither keratinase alone nor intracellular soluble substance with disulfide-reducing activity can completely degrade feathers, and that the presence of living cells is important for complete degradation 45. During the degradation process, the cells adhere to the surface of the plume, indicating that contact between living cells and the feather is advantageous for 5



degradation. This is possibly due to the continuous supply of reductants secreted by the cells to break disulfide bridges. The above phenomenon is also described in the study of Malviya et al 41. The biomembrane potential theory relies on the activity of living cells to generate an infinite reducing power for destroying disulfide bonds, as extracellular secreted keratinase or keratinase plus other intracellular reducing substances cannot effectively degrade keratin on their own 46. However, current research on this theory is scarce and it is difficult for researchers to determine how disulfide bonds are reduced. Mechanical pressure theory The mechanical pressure phenomenon usually occurs in microorganisms that can produce mycelia 41. The mycelium adheres to the surface of keratin and continuously penetrates the keratin substrate, destroying the dense keratin structure 47. This process is usually divided into two stages; in the first stage, the mycelium invades between or below the epidermal layer of keratin and grows longitudinally along the keratin fiber axis. The growth tension of the mycelium causes swelling and rupturing of the epidermal layer, forming protrusions of varying sizes 48. At this stage, the epidermis is shed with broken scales remaining, leaving an epidermis that is almost destroyed completely. The second stage involves the invasion of the cortex by the mycelium. The mycelium acts on the bonding matrix and the cell membrane, first dissolving the surface layer of the giant fiber and then separating the microfiber and the bonding matrix by the growth expansion force of the mycelium 49. The microfibers are then dissolved as well. Although the mechanical pressure brought about by mycelium growth is the main force behind the destruction of the keratin dense structure, the dissolution of keratin is attributed to the action of keratinase 34, 50. This is supported by cytological signs of strong enzymatic activity, such as the 6


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presence of abundant mitochondria 51. In addition, the electron density around the tenacious portion is significantly increased 52, indicating that the reducing power generated by the electron exchange of the cell membrane promotes keratin degradation. When comparing fungi with and without keratin-degrading abilities, it was found that fungi that can degrade keratin can also produce fronds and borers 53 induced by stratified and resistant keratin substrates. Fronds and borers are the main force behind the mechanical destruction of keratin, after which a large number of hydrolase binding sites are exposed where keratinase and other hydrolyzing enzymes can begin the process of hydrolysis 54, 55. In addition, the mechanical disruption of mycelia occurs before the production of keratinase, which leads to a complete synergistic decomposition of keratin. Thus, mycelium growth is positively correlated with its keratin degradation efficiency 56. Thiolysis theory Breaking disulfide bonds requires the presence of an alkaline environment or a reducing agent 57, such as a chemical reducing agent or a biological enzyme with similar functions to disulfide reductases. Several reports have confirmed that the presence of a chemical reducing agent, such as βmercaptoethanol, thioglycollate, dithiothreitol, or sulfite, can easily break a disulfide bond 27, 38, 58. The thiolysis theory involves the secretion of sulfite by microorganisms during metabolism, which breaks keratin disulfide bonds and leads to further hydrolysis of the denatured protein by proteases. In the early stages of microbial fermentation during feather degradation, peptides containing thiol and thiocysteine residues can be detected. As the fermentation process progresses, the content of sulfite and sulfhydryl compounds in the fermentation broth gradually decreases while sulphate content increases 59. Furthermore, analysis of the amino acid composition of the keratin hydrolysate indicated that the cysteine content was limited, which appears contradictory as a large number of 7



keratin disulfide bonds were destroyed and cysteine was released. A potential explanation for this phenomenon is a metabolic process based on the cysteine dioxygenase (EC 1.13.11.20) homeostatic regulation of cysteine levels in eukaryotic cells 60 with pyruvic acid, sulfite, sulfate, hypotaurine, and taurine as metabolites 61. The thiolysis theory proposed herein is based on the production of sulfite through the process of cysteine metabolism (Fig. 1). During this process, the microorganism first produces sulfite through its own metabolism (e.g., sulfur metabolism) and then secretes sulfite to the extracellular passage in a manner to the sulfite efflux pump SSU1 62, 63. At the same time, a large amount of L-cysteine produced by disulfide bond reduction enters the cell and is converted to L-cysteine-sulfinate by cysteine dioxygenase 64. L-Cysteine-sulfinate is then converted to 3-sulfinyl-pyruvate by aspartate aminotransferase and decomposed to produce sulfite and pyruvate 65. Sulfite continues to be secreted extracellularly to reduce disulfide bonds, which results in an infinite cycle of sulfite and Lcysteine interconversion until keratin is completely degraded. Furthermore, due to the large number of disulfide bonds destroyed during keratin degradation, a high concentration of cysteine is produced. Because high concentrations of cysteine are toxic to cells, microorganisms capable of degrading keratin must be able to balance cysteine levels 66. This is therefore consistent with the finding that no, or only a small amount of cysteine was detected in the feather fermentation broth.

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Fig. 1. The cycle of L-cysteine metabolism during microbial degradation of keratin. L-cysteine enters the cell and is converted to sulfite in three steps. The sulfite is then transported out of the cell by means similar to the sulfite efflux pump (SSU1), continuing to act as a reducing force for keratin denaturation to help the bacteria break down keratin. The L-cysteine produced by keratin breakdown enters the cell again to form a circulation. Among the reported keratin-degrading microorganisms, almost all possessed metabolic pathways for converting cysteine to sulfite, indicating that this is a necessary process for microbial degradation of keratin. In future studies, the use of gene editing methods to silence or enhance key genes in the cysteine metabolic pathway to explore the differences in keratin degradation efficacy will be an interesting research direction. Enzymatic hydrolysis theory Keratinase from different microorganisms exhibits differences in type and characteristics. Using protein engineering techniques, researchers isolated and purified different pure keratinase from keratin hydrolysate. However, keratin cannot be hydrolyzed by pure keratinase unless a disulfide bond reductase or a similar reducing force exists, keratin proteolysis experiments using pure 9



keratinase have yielded similar results 27. Thus, disulfide bond reductase plays a decisive role in the degradation of keratin and must be continuously secreted during the entire decomposition process 67. Disulfide bond reductases that have been isolated and purified possessed similar functions but exhibited different sizes, properties, and were involved in different reactions 68. Our review will attempt to provide a general overview of the disulfide bond-reducing proteins in microorganisms to promote further disulfide bond reductase research. Based on the different types of reactions, there are seven common types of disulfide reductases (Fig. 2) (Table 1). Thioredoxin 69 and thioredoxin reductase, together with NADPH, constitute the thioredoxin reduction system. This system was originally used as a hydrogen ion donor for nucleoside dinucleotide diphosphate to synthesize ribonucleotide reductase. The thioredoxin redox system is present in all organisms, and similar enzymes have been isolated and purified from many prokaryotic and eukaryotic cells. Enzyme protein purification studies have shown that high-purity thioredoxin reductase acts as a flavoprotein to specifically reduce the disulfide bond sites of oxidized thioredoxin. Moreover, thioredoxin reductase is often called disulfide bond reductase. Cys-Gly-Pro-Cys is a universally conserved active site in protein sequences 70. Studies on the mechanism and kinetics of thioredoxin reductase have shown that its physiological effects are equivalent to the reducing agent dithiothreitol, which is possibly the major disulfide reductase in cells 71. In this system, thioredoxin reductase transfers electrons in NADPH to cysteine in the thioredoxin active site-peptide chain 72.

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Fig. 2. An overview of disulfide reductases and their different reaction types. Alkyl hydroperoxide reductase is homologous to thioredoxin reductase, especially at some conserved sites, and is likely a class of enzymes associated with thioredoxin reductase. Moreover, methionine sulfoxide reductase can specifically reduce free or protein-linked methionine sulfoxide to methionine 73. The glutathione and thioredoxin reduction systems are the main antioxidant systems in organisms. The thioredoxin reduction pathway is ubiquitous in bacteria, whereas the glutathione reduction system is absent in some bacteria. Glutathione reductase is a more targeted reductase that catalyzes the oxidation of glutathione mainly under the action of NADPH 74. In addition to thioredoxin reductase and glutathione reductase, dihydrolipoyl dehydrogenase is also a member of the flavoprotein family and is a disulfide bond reductase 75. The mechanism of

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dihydrolipoyl dehydrogenase oxidation relies on a ping pong reaction, also known as a doubledisplacement reaction. This type of reaction is characterized by an enzyme that binds a substrate and releases a product, leaving behind a substituted enzyme 76. The substituted enzyme then binds the second substrate and releases the second product, which finally returns the enzyme to its original state. Moreover, ribonucleoside diphosphate reductase 77 and phosphoadenosine phosphosulfate reductase 78 are also involved in the disulfide reduction process.

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Table 1 Characteristics of disulfide reductase Disulfide reductase

Microorganism

Alkyl hydroperoxide reductase

Escherichia coli, Saccharomyces cerevisiae, Bacillus subtilis Escherichia coli, Saccharomyces cerevisiae

Thioredoxin reductase

Glutathione reductase

Dihydrolipoyl dehydrogenase

Peptide methionine sulfoxide reductase Phosphoadenosine phosphosulfate reductase Ribonucleosidediphosphate reductase

Escherichia coli, Saccharomyces cerevisiae, Schizosaccharo myces pombe Bacillus subtilis, Saccharomyces cerevisiae, Corynebacteriu m glutamicum, Pseudomonas putida Escherichia coli, Streptococcus gordonii Escherichia coli, Schizosaccharo myces pombe, Bacillus subtilis Escherichia coli, Saccharomyces cerevisiae, Schizosaccharo myces pombe

Classification number EC:1.11.1.15

Molecula r weight 19.1-56.1 kDa

Molecular function Antioxidant, oxidoreductase, peroxidase

Refere nces

EC:1.8.1.9

20.7-34.2 kDa

Antioxidant, oxidoreductase, peroxidase

80

EC:1.8.1.7

37.0-67.7 kDa

Oxidoreductase

81

EC:1.8.1.4

48.1-54.0 kDa

Oxidoreductase

82

EC:1.8.4.11

23.3-35.6 kDa

Oxidoreductase

83

EC:1.8.4.8

27.6-30.3 kDa

Oxidoreductase

84

EC:1.17.4.1

40.0-99.5 kDa

Allosteric enzyme, oxidoreductase

85

13


79


Decomposition: keratinase hydrolysis In the second step when disulfide bonds are broken, keratin fibers are exposed and microorganisms can secrete different proteases, such as keratinase, pepsin, trypsin, and papain, to decompose these fibrous proteins into peptides and amino acids. Keratinase When the dense structure of keratin is disrupted by various denaturation methods, the keratindegrading strain begins to secrete keratinase to further degrade loose keratin. Keratinase is a proteolytic enzyme that specifically degrades keratin, meaning that it is more sensitive to keratin substrates than other proteases. This enzyme has a broad spectrum of substrates and completely dissolves many soluble and insoluble proteins, such as casein, albumin, heme protein, collagen, and globulin as well as wool and feathers 86. Expression of wild-type keratinase requires the induction of keratin, most of which is extracellularly secreted as only a few are intracellular enzymes 87, while keratinase production is inhibited when carbon and nitrogen sources are readily available in the system 88. Keratinase mainly acts as a serine protease or metalloproteinase 86 and its activity is inhibited by serine protease inhibitors (such as phenylmethylsulfonyl fluoride). Furthermore, most keratinases exhibit optimal activity at 40–60 °C and in neutral to alkaline pH, with very few being acidic proteases. Examples of microbial angular proteolysis under basophilic and thermophilic conditions have been well documented 26, 89, 90. When reviewing the history of keratinase research, we found that researchers were very interested in the separation of keratinolytic bacteria and their individual keratinase enzymes. This is because scientists and enzyme manufacturers are after super enzymes that can degrade keratin waste 86, 91. To this end, numerous different keratinase sources have been isolated, purified, and analyzed by mass spectrometry or protein sequencing. The intact keratinase sequences were then heterologously expressed in mature host cells to produce high yields of recombinant enzyme, but neither the crude enzyme solution nor the purified enzyme were very inactive against native keratin 92.

In this sense, keratinase seems to be a misnomer because it does not respond to its specific

substrate (Table 2). However, keratinase can degrade keratin in the presence of suitable reducing agents, such as β-mercaptoethanol and dithiothreitol. Therefore, it is extremely important to 14


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elucidate the mechanism of microbial decomposition of keratin. Only by understanding how keratin is broken down by microbes and what role keratinase plays can we achieve a qualitative leap in the biorecycling of keratin.

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Table 2 Characteristics of keratinase isolated from microorganisms capable of decomposing keratin

Strain

Culture method

Substrate

Aerobic, batch, 23°C Aerobic, batch, 37°C Aerobic, batch, 30°C Aerobic, batch, 37°C Aerobic, batch, 30°C Aerobic, batch, 37°C Aerobic, batch, 37°C Aerobic, batch, 37°C

Feather

Aerobic, batch, 55°C Aerobic, batch, 30°C Aerobic, batch, 32°C

Feather

Aerobic, batch, 35°C Aerobic, batch, 30°C

Feather

Substrate and Keratinase activity

Keratinase decompositio n keratin

Refere nces

Soluble keratin, 1728 U/mL Soluble keratin, 256 U/mL Soluble keratin, 69.0 U/mL Azocasein, 1750 U/mL Casein, 130 U/mL

NO

93

NO

90

NO

94

NO

95

NO

96

Feather, 379.65 U/mL Soluble keratin, 373 U/mL Feather keratin, 1500 U/mL

NO

97

NO/removed blood Requires DTT

98

Feather keratin, 400 U/mL Keratin azure, 265 U/mg Keratin suspension, 172.7 U/mL Chicken feathers, 5 KU/mL Azocasein, 1695.7 U/mL

Requires β-ME

99

NO

100

NO

101

NO

102

NO

103

Bacteria Stenotrophomonas maltophilia BBE11-1 Bacillus licheniformis BBE11-1 Xanthomonas sp. P5 Bacillus cereus Wu2 Serratia sp. HPC 1383 Bacillus subtilis DP1 Bacillus pumilus GRK Bacillus amyloliquefaciens K11 Actinomycetes and fungi Thermoactinomyces sp. CDF Streptomyces sp. Aspergillus niger Trichophyton sp. HA-2 Aspergillus parasiticus

Feather Feather Feather Milk Feather Feather Feather

Casein Feather

Feather

16


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Other factors Not only have various keratinases have been isolated, but also several factors with synergistic effects during keratinase hydrolysis of keratin. Some of these factors include β-mercaptoethanol 99 and dithiothreitol 27 as well as other enzymes such as papain, alkaline protease and trypsin 104, 105. These cofactors are involved in different aspects of keratin denaturation and decomposition and promote the complete breakdown of keratin.

Conclusions and Future Perspectives Wild-type bacteria and filamentous fungi are potential candidates for the degradation of keratin in fermentation engineering (see Table 1). However, they have the common disadvantage of limited keratin decomposition ability because of their low biomass and keratinase secretion efficiency. In addition, the unclear mechanisms of keratin microbial degradation pose a huge obstacle to the microbial treatment of keratin and our ability to exploit this high-quality protein resource. At present, synthetic biology and metabolic engineering strategies are ubiquitous and some excellent production strains have been engineered. For example, Escherichia coli and B. subtilis are fast growing and have a well-defined genetic background and several established genetic manipulation tools 106, 107. Nevertheless, engineering high-quality strains or super-enzymes that degrade keratin waste through the rapidly developing synthetic biology and metabolic engineering techniques remains attractive. To achieve this, we must uncover the mechanism by which microbes break down keratin. As far as the current methods for breaking disulfide bonds are concerned, thiolysis and enzymatic hydrolysis theories are considered the most reasonable and are relatively simple to exploit. Advances and improvements in genetic tools and the application of omics analysis have made it possible to use engineered strains for keratin degradation or even cell-free catalytic hydrolysis of keratin. As shown in Fig. 3, strategies for increasing the efficiency of the cysteine metabolic pathway through thiolysis and identifying and enhancing key enzymes in the pathway are summarized as follows, (1) overexpression of rate-limiting enzymes in the L-cysteine metabolic pathway or introduction of new metabolic pathways to increase sulfite conversion; (2) enhancement of transport pathways to increase sulfite secretion; (3) overexpression of disulfide reductases and proteolytic enzymes associated with keratin hydrolysis including keratinase; and (4) designing an in vitro keratin 17



decomposition system based on the synergistic effect of keratinase and reducing agents.

Fig. 3. Systems and synthetic biology guide to the metabolic engineering of microorganisms for manufacturing dominant strains and super-enzymes for keratin degradation. Nevertheless, implementing these strategies faces several obstacles. First, the pressure exerted 18


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by overexpression of rate-limiting enzymes or introduction of a new pathway on the host and the flux relationship between the rate-limiting enzymes must be balanced. Metabolic engineering and synthetic biology offer several viable options to overcome this, including genetic screening, substitution, recombination, mutations, and the construction of new high-efficiency pathways 108-110. Second, identifying enzymes that are beneficial for keratin degradation is critical. This requires utilization of omics techniques that combine studying genomes, transcriptomes, proteomes, and metabolomes 111, 112. By analyzing the omics of keratin-degrading strains, we can identify differential genes and proteins to determine key genes and enzymes in the keratin degradation pathway. Third, the renewal of fermentation engineering technology is needed to provide real-time control of balanced cell growth and nutrient-producing ratios and processes, which would make the microbial degradation process of keratin visible 93. This control of the process can lead to precise results and more economical production methods. In the end, we hope to engineer high-quality strains that can be used in industrial mass production or to achieve cell-free reaction processes based on keratinase catalysis, which can maximize cost savings and achieve green production.

Author contributions ZP performed the majority of the literature survey and content design in this manuscript, as well as wrote most of the manuscript. GD and JC contributed to the discussion, writing and revision of the manuscripts. JZ: contributed to the theoretical summary, discussion and suggestions during the work, and revised the final versions of the manuscript. All authors read and approved the final manuscript.

Acknowledgments This work was supported by the National Key Research and Development Program of China (2017YFB0308401), the National Natural Science Foundation of China (31470160), the 111 Project (111-2-06), the National First-class Discipline Program of Light Industry Technology and Engineering (LITE2018-08), the project of Integration of Industry, Education and Research of Jiangsu Province, China (BY2016022-39), the grant from Pioneer Innovative Research Team of Dezhou, and the Open Project of Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University (KLIB-KF201706). 19



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Abstract Graphic

Synopsis Biorecycling is considered a future for the sustainable development of keratin waste.

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Photographs and Biographies

Zheng Peng received his master's degree from Yunnan Normal University in 2016 and is currently pursuing a doctoral degree under the guidance of Professor Jian Chen at Jiangnan University. His research interests focus on the design of biocatalysts and the green recycling of waste.

Associate Professor Juan Zhang his Bachelor’s, master’s degree and Ph.D. from Jiangnan University. She was a postdoctoral fellow at the American Institute of Systems Biology. She is a member of the American Society of Chemical Engineers (AIChE) and a member of the American Academy of Dairy Sciences (ADSA). She has published more than 50 research papers. Her recent research focuses on the development of microbial metabolic engineering based on systems biology and the development and application of novel food enzyme preparations.

Professor Guocheng Du received his Bachelor’s degree from Yangzhou University, master’s degree and Ph.D. from Jiangnan University. He was a visit scientist at Hawaii University. Prof. Du has about 300 publications/communications, which include 68 patents, 10 books, 176 original and review papers, etc. He is associate editors of Journal of the Science of Food and Agriculture, and Microbial Cell Factories, and Board member of Bioresource Technology. Prof. Du’s current main research focus is on bioprocess engineering and metabolic engineering that lead to deal with the design and modification of microorganisms, and development and optimization of processes for the manufacturing of bio-products such as industrial enzymes, nutraceuticals and bio-chemicals.

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Professor Jian Chen received his Bachelor’s degree from Tsinghua University, master’s degree and Ph.D. from Jiangnan University. He was a visiting scholar at Osaka University, Tokyo Institute of Technology and Inha University. Currently, he is the Professor of School of Biotechnology in Jiangnan University. He is an academician of the Chinese Academy of Engineering. He is the Chief Editor of Food Bioscience, and serves on the Board of Editors for Process Biochemistry. He also honored International Academy of Food Science and Technology Fellow (IAFoST Fellow) and Fellow of International Bioprocessing Association (FIBA). Prof. Chen focuses on solving key scientific and engineering problems in fermentation engineering to realize efficient fermentation process with high titer, high yield, and high productivity. Systems and methods of microbial cell factories construction in combination with theories and technologies of fermentation process were intensively investigated by Prof. Chen.

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Keratin Waste Recycling Based on Microbial Degradation

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