Relevance of Microbial Enzymes in Textile Industries Emphasizing Metabolic Engineering Panorama
Dipankar Ghosh and Priyanka Talukdar
Introduction
Textile industries are one of the major sources of biochemical waste generators from cotton softening, removal of size lubricants, textile desizing, enzymatic scouring, denim finishing, pilling of fiber, fuzz fiber removal, treatment of wool, degumming of silk, surface modification of synthetic fibers or synthetic fiber modification, polyacrylonitrile (PAN) surface alterations, dyes removal, bleaching of textile products and bleach liquid effluent downstream processing, fabric defragmentation or desizing and bleaching of chemical dyes. These biochemical waste materials of textile industries-derived have huge negative impacts on the environment and ecological balance (Ahuja et al. 2004). In this scenario, textile industries have enormously profited from the usage of potential enzymes in both product quality improvements and environmental pollution minimization (Choi et al. 2015). In the textile industry', cotton fiber pretreatment and fiber polishing off approaches are predominantly hydrolases and oxidoreductases. Hydrolase group of enzymes indulges in biopolishing and bio scouring of fabric, wool antifelting, softening of cotton fibers, finishing with denim quality, and modification of synthetic fibers (Figure 13.1). The hydrolase enzyme class includes cellulase, cutinase, pectinase, lipase, esterase and amylase (Araujo et al. 2008; Chen et al. 2013). On the contrary, the oxidoreductases enzyme class includes laccase, catalase, and lignin peroxidase. These classes of enzymes participate in fiber bioleaching and bleach termination, decolourization of chemical dyes, and
FIGURE 13.1 Enzyme-based pretreatment approaches for improving textile fiber quality.
wool finishing (Araujo et al. 2008; Chen et al. 2013). However, existing key industrial microbial enzymes are insufficient enough to fulfil textile industrial sustainability (i.e. higher quality textile products) due to lower substrate specificities, product inhibition, enzyme stability, lower catalytic efficiencies and lack of efficient naive enzymes time to time. Hence, diverse approaches (i.e. rational enzyme design, metabolic systems biology) have been applied to resolve the aforementioned global issues. Therefore, the aim of this current work is to summarize novel and advanced approaches on pretreatments and polishing approaches in textile industries. Moreover, the current chapter will also include an emphasis on naive and/or newly isolated novel enzyme engineering and redesigning towards application in textile industries.
Pretreatment and Polishing Approaches in Textile Industries
Textile desizing is the removal of size or adhesive materials which coat warp threads of cotton or blends as a protective barrier during weaving. Before enzymatic sizing, acid, alkali or oxidizing agents at high temperatures usually work as desizing agents of textile fabric, constituents such as starch and its respective derivatives are fantastic films generating efficacy, easy availability (Feitkenhauer et al. 2003). However, the chemical-based desizing approach is not up to the mark as it causes unwanted degradation of cotton fibers, reduction in natural texture and quality decay of cotton fibers. To this end, enzyme-based textile desizing is preferable considering its higher efficacies and selectivity without adverse effects on textile fiber quality
(Cegarra 1996; Etters and Annis 1998). Moreover, this approach minimizes the waste chemical disposals towards balancing the environmental ecosystem. Cotton fabric wettability has been ameliorated via scouring methods using biocatalysts (i.e. enzymes). Unprocessed cotton fibers contain waxes, pectin, hemicellulose, etc., as non-cellulosic dross. These non-cellulosic impurities provide hydrophobic features to untreated cotton fibers (Freytag and Dinze 1983; Batra 1985; Etters et al. 1999). However, enzymatic scouring is advantageous over chemical treatments as it retains the exact cellulose strength and weight in textile fiber after treatment. Moreover, the generated waste disposal contains lower organic loads (i.e. biochemical oxygen demand) quantity of salt concentrations (Buschle-Dilleret al. 1998). Denim finishing is a textile fiber treatment process used to slightly generate the worn look of cloth. Sodium hypochlorite or potassium permanganate are chemical agents commercially known as pumice stones.
Biopolishing accelerates the amelioration of textile fiber quality through shortening blurriness and pilling features of cellulosic fiber. The main practical concern of bio-polishing is to eradicate the microfibrils of textile cotton fibers (Cavaco-Paulo 1998; Cavaco-Paulo et al. 1996; Lenting and Warmoeskerken 2001). Resctrictive physicochemical phenomenon is responsible for this kind of feature in woolen fibers. Chloride-Hercosett method provides resistant properties to woolen fibers to withstand shrinkage behaviours (Heiz 1981). This approach deals with lower weight loss, lower damage and higher antifelt ability to woolen fibers. However, this approach suffers from poor handling quality, minimal durability, fiber yellowing, dyeing and environmental issues involve in the disposal of organic halogen wastes (Julia et al. 2000; Schlink and Greeff 2001). Woolen fibers gain shrinkage tolerance, retention of tensile strength, smoothness, handle features, wettability, resistance to detergents and consistent chemical dye consumption via usage of transglutaminase enzymatic (TGs) treatments (Cortez et al. 2004, 2005). Degumming of raw silk fibers is an efficient approach for removal of proteinaceous fiber cementing material (i.e. sericin). There are several alkaline, acidic and neutral degumming agents available to improve the silk surface features including texture, handle, shine and smoothness. However, this approach has very limited industrial applications as it does not show proper efficiency to remove the silk fiber protein sericin (Freddi et al. 2003; Arami et al. 2007). Synthetic fibers occupy almost more than 50% of the textile fiber global market. The most promising synthetic fibers include polyacrylonitrile (PAN), polyamine (PA) and polyethylene terephthalate (PET), which reflect comparatively better tensile strength of the fiber, higher resistance towards harsh chemical agents, lower shrinkage and abrasion phenomena. Although synthetic fibers show few pit- falls, it is likely higher hydrophobic and rigid crystalline fiber nature influences the post-processing hurdles (i.e. efficiency of colouring dyes and wearing discomfort in consumers) (Jaffe and East 1998: Yang 1998: Frushour and Knorr 1998). Textile bleaching of natural fibers occurs through the decolourization of natural pigments to attain white outlook of cotton or textile fibers. Hydrogen peroxide applies as bleaching reagent at a higher temperature and higher alkaline pH range. However, higher temperature and pH reduce simultaneously the quality and texture of textile fibers. To avoid this issue, biological enzymes, likely laccase, applies to resolve this event instead of chemical bleaching agents to ameliorate cotton fiber or textile fiber whiteness through flavonoids oxidation. As far as industrial concerns, this approach minimizes textile fiber deterioration and makes the approach economically sustainable
(Tzanov et al. 2003). As an addendum, ultrasound system has been incorporated in this existing segment to improve biological enzyme diffusion across the textile fibers from the liquid phase to the fiber surface. Therefore, this combined advanced approach of ultrasonication cum bleaching pretreatment improves the all quality and texture of textile fiber through proper naive colour oxidation as well (Basto et al. 2007). After bleaching, post-treatment involves cotton fiber defragmentation and scouring method in textile industries. Usually reducing agents or water have been applied to spiflicate hydrogen peroxide from the bleach liquor. Recently it has been found that catalase enzymes work very nicely to destroy excess unused hydrogen peroxide (Fraser 1986). However, incorporation of immobilization approach on these potential catalase enzymes (as reducing agents) minimizes cost involvement in hydrogen peroxide removal from bleach liquor (Costa et al. 2001; Paar et al. 2001; Fruhwirth et al. 2002).
Application of Novel Enzymes in Textile Industries through Redesigning and Bioengineering Approaches
The naive enzymes are the primary gold mine for all essential enzymatic conversion towards improving basic processing steps (i.e. cotton softening, removal of size lubricants, textile desizing, enzymatic scouring, denim finishing, pilling of fiber, fuzz fiber removal, treatment of wool, degumming of silk, surface modification of synthetic fibers or synthetic fiber modification, polyacrylonitrile (PAN) surface alterations, dyes decolourizations, bleach effluent treatments, fabric desizing and bleaching of chemical dyes). The main purpose is to ameliorate the efficacy of the aforementioned avenues for ameliorating quality upon fiber texture. However, catalytic efficiencies of naive enzymes extracted from living microbial regimes are not quite up to the mark to fulfil the current textile industrial requirements. Recent advances in genomics, transcriptomics, proteomics, metabolomics, materiomics and fluxomics open up highly organized biological dataset which permits data mining to generate efficient biocatalysts for textile industries. Moreover, it has also been clearly evident that more than 50% of industrially viable potent enzymes are genetically designed to generate metabolically engineered efficient microbial cell factories (Hodgson 1994). In practice, enzyme (protein) engineering and metabolic engineering applications on these naive enzymes help to attain higher catalytic or specific activities, pH tolerance, oxidative stability, chelator resistance and temperature tolerance following advanced techniques. These advanced technologies incorporate site-directed mutagenesis, homology modelling, and random mutagenic approaches (Figure 13.2).
Amylases are one the most established enzyme systems in textile industries towards fiber desizing of fibers. These enzymes speed up the starch containing fiber size remotion of yarn to improve weaving process. The a-amylase of Bacillus licheniformis improves its catalytic efficiencies following random mutagenesis through substitution of two independent amino acids (i.e. Hisl33Tyr, Hisl33Ile, Ala209Val and Ala209Ile). This molecular substitution in the catalytic site of a-amylase of B. licheniformis enhances thermostability through improved enzyme structure compactness and pull in entropy. In another study, B. amyloliquefaciens
FIGURE 13.2 Engineering of naive enzyme and its impact on textile industries.
a-amylase is subjected to amino acid substitution in two regions in catalytic domains (i.e. Lys269Ala and excision of Argl76 and Gly 177). This alteration enormously improves the thermostability of a-amylase of B. amyloliquefaciens (Suzuki et al. 1989; Igarashi et al. 1998). Cysteine and methionine are the two most oxidative-sensitive amino acids in enzymes. In this context, a-amylase of Bacillus sp. (KSM-1378) attains higher oxidative tolerance through site-directed mutagenesis on those two amino acids. Site-directed mutagenesis on a-amylases reduces oxygen susceptibilities through alteration of certain amino acid residues likely cysteines and methionine (Brosnan et al. 1992; Brzozowski et al. 2000). Deletions of Ile214 and Gly215 residues in a-amylase enzyme of Geobacillus stearothermophilus US100 strain ameliorates thermal stability, chemical oxidation resistance and minimizes lower calcium requirement (Ben Ali et al. 2001, 2006; Khemakhem et al. 2009). Pectinase is another class of enzyme useful in textile industries towards bioscouring of textile fibers. Pectinesterases, polygalacturonases and polygalacturonate lyases are the three major classes of pectin degraders (Li and Hardin 1997; Tzanov et al. 2001; Choe et al. 2004; Ibrahim et al. 2004; Karapinar and Sariisik 2004). However, naive pectinase suffers from lower enzymatic activity, temperature stability and pH stability issues. Incorporation of mutations in certain amino acid moieties, likely alanine, tyrosine, histidine, leucine, asparagines, serine, and valine, with corresponding locations (Ala-118His, Tyrl90Leu, Alal97Gly. Ser208Lys, Ser263Lys, Asn275Tyr, Tyr309Trp and Ser312Val) in pectinase enzyme improves bioscouring (Solbak et al. 2005). This approach enhances the high-temperature bioscouring process with lower pectinase usage in textile industries.
In the textile industry, bacterial and fungal cellulases have been used for denim finishing. However, the yield of fungal cellulases is comparatively higher than bacterial cellulases (Knowles et al. 1987) though fungal cellulases show maximal catalytic activities at acidic microenvironments. This feature limits the implementation of fungal cellulase enzyme systems at neutral or alkaline environments in textile industries. This is the major driving force to engineer microbial cellulases for improving catalytic efficacies at alkaline pH. Trichoderma reesei cellulases (Cel7A) improve its catalytic potential at higher pH through the introduction of a few mutations through site- directed mutagenesis (i.e. Glu223Ser/Ala224His/Leu225Val/Thr226Ala/Asp262Gly) (Becker et al. 2001).
In another study, it has been shown that Trichoderma reesei endoglucanase (Cel5A) catalytic ability has been improved at comparative higher pH range through a single substitution of Asn342Thr. Further, Trichoderma reesei endoglucanase (Cel5A) shows around fivefold higher enzymatic activities at higher pH range through the generation of various engineered variants (i.e. Leu218His, Glnl39Arg, Asn342Thr. Glnl39Arg, Leu218His, Trp276Arg and Asn342Thr). These modified attributes attain in those variants occur due to helix stability and alterations in electrostatic affinities between conserved catalytic sites and initial substrates (Qin et al. 2008). Cellobiohydrolase (Cel7B) of thermophilic fungus Melanocarpus albo- myces undergoes random mutagenesis in Ala30Thr, Glyl84Asp and Ser290Thr to gain thermal stability of this enzyme while heterologously in Saccharomyces cere- visiae (Voutilainen et al. 2007). It has been evident that incorporation of disulfide linkages in cellulase enzymes ameliorates the thermostability towards potential application in textile fiber texture and quality improvements at a higher temperature. Few promising residues for this type mutation include Gly4Cys, Met70Cys and Ser209Thr (Voutilainen et al. 2009). In a similar manner, a disulfide bond has been incorporated in protease subtilisin in between cysteine residues (Cys61 and Cys98) to improve the thermostability (Takagi et al. 1990). Site-directed mutation in Asn218Ser and Ser236Cys in subtilisin E protein increases thermostability up to 60°C which is around fourfold higher compared to naive subtilisin E protease (Wang et al. 1993; Yang et al. 2000a, 2000b).
In textile industries, most protein engineering approaches have been applied in esterases or lipases to deal with surfactant compatibility and oxidative stability. However, lipase enzymes are comparatively stable in oxidative stress conditions compared to proteases or amylases. While Met72Leu substitution has been incorporated in the lipase of Candida antarctica B, it ameliorates oxidation stability due to peroxy-octanoic acid. In a similar fashion, substitution of methionine in lipase of Pseudomonas sp. restricts the oxidative inactivation (Patkar et al. 1998). The synthetic fibers surface alteration occurs due to cutinase enzyme activities in textile industries. A substitution mutation in leucine and asparagines residues (Leu81Ala, Asn84Ala, Leul81Ala, Leul82Ala, Vall84Ala and Leul89Ala positions) in cutinase from Fusarium solani enlarges the catalytic pocket to improve the better substrate (larger synthetic fiber polymeric chains) binding or interactions towards improving synthetic fiber texture and quality (Araujo et al. 2007).
Future Outlook with a Special Emphasis on Metabolic Engineering and Synthetic Biology
In last few decades, an enormous number of processes have been implanted so far for improving textile industrial overall turnover. Enzyme engineering is one of the most potential segments in this progression trend. Commercial success has already been achieved, likely amylases in desizing, cellulases, and laccases in denim finishing, etc. However, productivity and catalytic efficiencies need to ameliorate further to generate sustainable bioprocessing platform in textile industries. In this context, metabolic engineering and synthetic biology could play a pivotal role in generating compact efficient microbial cell factories. Figure 13.3 depicts the general predictive workflow for implementing synthetic biology and metabolic engineering technologies. This approach helps to generate synthetic operon including promoter, ribosomal binding site, and the gene of interests (corresponding to engineered textile enzymes), terminators, and
FIGURE 13.3 Synthetic biology and metabolic engineering tentative predictive implementation in textile industries.
selectable markers. However, these synthetic operons have to be functionalized in a suitable microbial host. To this end, a paradigm shift is highly necessary where a microbial cell factory has to be generated to process and maximize the quality and texture of textile fibers. Hence, growth and metabolic networks in microbial hosts need to be understood properly. Genome-scale modelling. Omics approaches can also accelerate the process of microbial cell factory' generations to understand the cellular processes of organisms towards textile industrial applications. Based on this current scenario, future research progression should be continued towards synthetic and natural textile fiber bio-reformations using novel approaches, likely synthetic biology and metabolic engineering, in textile industries.
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