Keywords

1.1 Introduction

Synthetic dyes have become an important part of life as they have several advantages over natural dyes; for example, they are very stable as a result of the formation of covalent bonds with fiber, whereas natural dyes are less permanent and difficult to apply. There are approximate 10,000 synthetic dyes available on market with annual production of 7 × 105 metric tons (Campos et al. 2001). Significant amounts of synthetic dyes are used by the textile and dye industries; 15–20% of the dyes used in the dye industry are unable to bind to fabric and are released as effluent and contaminate nearby water sources (Husain 2010). Water is a natural resource that is required in almost all household and industrial uses. Industrial effluents that contain mainly dye compounds are among the serious causes of water pollution, making water unfit for aquatic life (Hassani et al. 2008; Chanyal and Agrawal 2017). Many synthetic dyes are also carcinogenic and toxic to human and aquatic life as they are made up of compounds like benzidine and aromatic compounds. Cleavage of some of the most widely used commercial dyes, azo dyes, resulted in the formation of amine, which is mutagenic to humans (Asgher et al. 2006). Direct discharge of contaminants from several industries to the environment is the main cause of water pollution, so the removal of these compounds from the environment is essential for sustainable development (Aksu and Donmez 2005; Balaji et al. 2012).

The methods used for dye treatment are classified into three categories: physical, chemical, and biological methods (Robinson et al. 2001). The physical and chemical methods are quite expensive not very effective for the treatment of dyes from wastewater (Si et al. 2013). Because of their disadvantages, like their high cost, associated waste disposal problems, and lower adaptability, these methods are not well suited for the treatment of dye-contaminated water (Asgher et al. 2008). Hence, the production of cost-effective, environmentally friendly, and efficient biological methods is necessary for effluent treatment.

Bioremediation -based methods using microorganisms for the treatment of effluent could be an efficient method as several bacteria and especially fungi and their enzymes are reported to have potential in decolorizing textile dyes (Forgacs et al. 2004). Bioremediation as a technology enjoys wide public support owing to its low cost and environmental friendliness. Among microorganisms, endophytes that reside in plants grown in contaminated sites may be a promising biological organism for the elimination of dye or for the decolorization of dye produced by several industries. Other important functions of endophytes include the ability to augment the thermal and salinity tolerance of host plants, increasing their ability to live in extreme environmental conditions (Redman et al. 2002). Rodriguez et al. (2004) reported that some tropical trees can increase their resistance by hosting endophytic microorganisms. Hence, bioremediation , which involves the use of microorganisms in the degradation or absorption of pollutants, is one of the most effective alternatives for the removal or reduction of industrial waste (Mcmullan et al. 2001; Singh et al. 2014). Most microorganisms, especially fungi and their enzymes, have the potential to degrade dyes by producing enzymes like laccases (Forgacs et al. 2004). Several researchers have reported that laccases produced by endophytic fungi have the ability to degrade azo dyes (Chanyal and Agrawal 2017; Ngieng et al. 2013; Novotny et al. 2004). Ngieng et al. (2013) reported on 20 endophytic fungi from Melastoma malabathricum with the ability to decolorize 5 different azo dyes to varying degrees. This chapter provides an overview of various forms of dye degradation using endophytic fungi, presents a biotechnological approach to using these fungi, and discusses their future prospects.

1.2 Endophytes

The groups of microorganisms that inhabit different parts of plant tissues without causing any disease symptoms are known as endophytes (Gouda et al. 2016; Schulz and Boyle 2005; Specian et al. 2012). There are no apparent symptoms of disease found in plants hosting endophytes. Hence, endophytes exhibit strong positive associations with their host plant (Nair and Padmavathy 2014).

Endophytes are well known to produce a wide variety of bioactive compounds, including antibiotics, antitumor and immunosuppressive agents, plant growth hormones, and biological substances like enzymes, alkaloids, and vitamins, which can play a vital role in the pharmaceutical and agriculture industries (Uzma et al. 2018; Mishra et al. 2017; Wu et al. 2010). Endophytes are reported to produce compounds having the ability to inhibit bacterial and fungal pathogens and could help in protecting plants against phytopathogens (Mishra et al. 2016; Rya et al. 2007; Staniek et al. 2008; Rai et al. 2014). Interestingly, few endophytes share the compounds produced by plants as well (Kumara et al. 2014; Shweta et al. 2014). These findings demonstrate that endophytes are present within plant tissues and subsist as reservoirs of bioactive metabolites (Tan and Zou 2001; Priti et al. 2009).

Endophytes are categorized into bacteria and fungi . More than 200 bacterial genera have been identified as endophytes distributed among the phyla Actinobacteria, Proteobacteria, and Firmicutes (Golinska et al. 2015). Among these, the genus Streptomyces from the phylum Actinobacteria is the most dominant of genera that have been isolated in large volume from medicinal plants as endophytes (Zothanpuia et al. 2018; Zhao et al. 2011; Golinska et al. 2015). Endophytic fungi are classified into clavicipitaceous and nonclavicipitaceous . Clavicipitaceous fungi are those that infect certain grasses present in cool regions, and nonclavicipitaceous fungi are isolated from healthy tissues of nonvascular plants like ferns and their allies, conifers, and angiosperms. Ascomycota and Basidiomycota represent the two main groups of nonclavicipitaceous fungi (Jalgaonwala et al. 2011; Bhardwaj and Agrawal 2014).

1.3 Dyes

Dyes are complex colored organic compounds mainly used in the textile, leather, paper, and food industries (Harvey and Keith 1983). Since dyes are the major component used in these industries, the effluents discharged are mainly composed of dye compounds that act as the main source of organic pollutants released into the environment that disturb normal biotic as well as abiotic systems (Muthezhilan et al. 2014). Dyes can exist in many different formed, but they include a minimum of one azo (N=N) bond. For instance, dyes having one N=N bond are known as azo and monoazo dyes, whereas dyes having two and three N=N bonds are known as diazos and triazos, respectively. Azo groups linked with naphthalene and benzene rings give dyes their color and make various shades and intensities possible (Zollinger 1991). Dyes are broadly divided into synthetic and natural dyes, and do not have a definite chemical structure. Chromophores give fibers their color, whereas auxochromes fixed colors on fibers (Banat et al. 1996; Welham 2000). Dye processing occurs largely in three steps: preparation, dyeing, and finishing. Different types of dye processing are carried out based on the nature of the fiber and the properties of the dyes, like the chemical structure, fixing property compatibility with the materials to be used, classification, and pigments used (Guaratini and Zanoni 2000). Large amounts of chemical compounds are used in each step of dye processing (Moore and Ausley 2004).

Dyes cause serious problems related to the release of industrial effluents and the removal of dyes and other chemicals pollutants (Balaji et al. 2012). Most dyes can affect human beings and animals by causing allergies, cardiovascular problems, gastrointestinal problems, DNA damage, and cancer (Harvey and Keith 1983; Mittal et al. 2006). To address these problems, many researchers are trying to develop a simple, eco-friendly, and cost-effective techniques for dye degradation, but this remains a very difficult and complex challenge (Pant et al. 2008).

1.3.1 Types of Dyes

1.3.1.1 Textile Dyes and Their Importance

Over 100,000 colors of synthetic dyes are produced commercially, and over 7 × 105 tons of dyes are produced every year worldwide (Zollinger 1987). Throughout the world, dyes are heavily utilized in the textile, cosmetic, paper, pharmaceutical, and food industries along with additives in the petroleum industry (Husain 2010). Synthetic dyes are broadly used in the textile and dyeing industries. When dyes are processed, approximately 15–20% of the dyes does not bind with fibers and as a result is lost in effluent (Husain 2010). Maas and Chaudhari (2005) suggested that around the world, approximately 280,000 tons of textile dyes are released from industrial sewage every year. The released textile dyes are transferred in rivers or lakes, which can cause water pollution at very low concentrations of 1 ppm (O’Neill et al. 1999). The accumulation of dye in water can reduce sunlight penetration, which in turn can reduce photosynthetic activity. Moreover, accumulated dyes unfavorably influence biological oxygen demand (BOD ), chemical oxygen demand (COD ), and dissolved oxygen, which creates a toxic environment for aquatic organisms (Khan and Bhawana 2013; Sen et al. 2016). Most dyes have a hard structure and are of synthetic origin, so bleaching dyes is complicated.

1.3.1.1.1 Natural Dyes

Natural dyes are obtained from natural resources like different parts of plants, animals, insects, and minerals without application of any chemical treatment. Indigo dye from the plant Indigofera tinctoria, lawsone obtained from Lawsonia mermis, carajurin obtained from Bignonia chica, and carotenoids are examples of natural dyes (Vankar 2000). Synthetic dyes are widely used in various industries, but they are also known mutagens, allergens, and carcinogens, whereas natural dyes do not have any toxic effects. Dyes obtained from natural resources like plants, animals, or minerals are very easy to wash and clean, and for this reason natural dyes are very eco-friendly (Vankar 2000). In addition to their dyeing properties, natural dyes also have a broad range of medicinal properties. These days, there is growing awareness of the use of natural dyes and dye producer plants. Owing to their nontoxic nature, medicinal values, and less harmful side effects, natural dyes are now applied commonly in everyday food products and in the pharmaceutical industry (Chengaiah et al. 2010; Shahid et al. 2013).

In India, over 400 plants can produce dye. For instance, a brilliant, naturally occurring yellow dye is produced from turmeric, which also has strong antiseptic activity to cure skin ailments (Siva 2007). Natural dyes are commonly applied in food coloring, leather, natural protein fibers like wool, silk, and cotton textiles, and even in drugs and cosmetic products owing to their nontoxicity. Due to the evolution of synthetic dyes , the use of natural dyes worldwide in textiles has been limited to artisan or craftsman uses, small-scale or cottage-level dyers, and printers, and some producers manufacture environmental friendly dyes for textile production (Chavan 1995). Natural dyes require a compound known as a mordant used to set dyes on fabric, which prevents the dye from bleeding or being washed out easily. Mordants facilitate chemical reactions for the absorption of dyes between dyes and fibers (Siva 2007).

Most natural dyes are found from plants that produce various colors. Most plant parts like the seeds, leaves, bark, roots, flowers, fruits, and so forth produce dyes. Interestingly, 2000 pigments are made by different plant parts. Of these, only 150 have been commercially sold on the market. In India, approx. 450 taxa are known to produce dyes, of which the 50 best-known plants produce natural dyes. Briefly, Siva (2007) reported that most dyes are obtained from roots (n = 10), followed by wood (n = 8), flowers and fruits (n = 7), leaves (n = 5), bark (n = 4), seeds, and gum and resins (n = 3). To date, few dyes have been synthesized from natural sources; for instance, few plants, like Lithospermum erythrorhizon and Bixa Orellana, can be used to derive dyes for lipstick and indigo for eye shadow. Siva (2007) demonstrated that the occurrence of dyes in plants varies depending on the age of the plant and the season. Many plants, such as Punica granatum L., which have high antimicrobial potential due to the occurrence of high amounts of tannins, can be used to extract natural dyes. Moreover, several other plant dyes, such as lawsone, commonly known as henna obtained from Lawsonia inermis L., Juglone from walnut, and lapachol from alkanet, demonstrated antibacterial and antifungal properties (Siva 2007). Another advantage of natural dyes is that some have antimicrobial potential against pathogens. Singh et al. (2005) reported on the antimicrobial activity of five natural dyes (Acacia catechu, Kerria lacca, Quercus infectoria, Rubia cordifolia, and Rumex maritimus) against Klebsiella pneumonie, Escherichia coli, Proteus vulgaris, and Pseudomonas aeruginosa. Of these, Quercus infectoria, a natural dye, showed the highest antimicrobial activity (Singh et al. 2005).

1.3.1.1.2 Synthetic Dyes

Synthetic dyes are widely used in various industries such as textiles, leather, beauty care products, food, pharmaceuticals, and paper printing . The most toxic compounds that create environmental pollution include azo, antraquinone, heterocyclic, triphenylmethane, and phthalocyanine dyes. Interestingly, 10–15% of dyes are removed in wastewater in these industries while dyeing and washing textiles (Husain 2010). This wastewater can cause several diseases around the world. Moreover, the release of wastewater can pollute both ground and surface water, which may lead to various health issues in both humans and animals because they are considered very toxic, mutagenic, and carcinogenic. Therefore, it is immensely important to search for alternative methods to degrade dyes easily from wastewater treatment systems. The degradation of dyes using physical and chemical methods is not very effective owing to the high costs and time and because the method could be methodologically demanding (Ben Younes et al. 2012). Nowadays, most researchers are trying to use microorganisms to degrade dyes (Eichlerova et al. 2005).

Of the 100,000 commercially available dyes, at least 10–15% of the used dye traps in the environment in the form of wastes become major environmental pollutants (Zollinger 1987; O’Neill et al. 1999; Robinson et al. 2001). Among synthetic dyes , azo reactive dyes are the most prevalent types that are soluble in water. Azo dyes have the greatest range of color structures and colors among the synthetic dyes and are usually resistant to biodegradation by aerobic methods. Most of these dyes become toxic only after being released into aquatic environments, where they may be converted into harmful carcinogenic amines (Spadaro et al. 1992; Chung and Stevens 1993). Hence, they are considered xenobiotic compounds due to their resistance to natural microbiological degradation (Stolz 2001). There are more than 3000 azo dyes, of which Maxilon Blue GRL, Astrazon Red GTLN, and Sandolan Yellow are widely used in certain industries like textiles, leather, cosmetics, food coloring, and paper production (Elbanna et al. 2010). It was estimated that approximately 10% of dyes do set in fiber during the dyeing process and are released directly into the environment, causing major harm (Asad et al. 2007) and complications like mutagenicity, genotoxicity, and carcinogenicity to living beings (Puvaneswari et al. 2006).

White rot fungi are commonly used as decomposers of lignin and have the potential to degrade various organic pollutants, including pesticides, polycyclic aromatic hydrocarbons (PAHs) , polychlorinated biphenyls and synthetic dyes (Bezalel et al. 1997; Sack et al. 1997; Novotny et al. 2000; Pointing 2001). They are commonly used in nonspecific, free-radical-mediated processes that utilize enzymes to degrade lignin and other structurally similar compounds (Chagas and Durrant 2001). Many researchers have reported on the decolorization and degradation of synthetic dyes from various ligninolytic fungi such as Phanerochaete chrysosporium (Couto et al. 2000; Podgornik et al. 2001; Conneely et al. 2002; Moldes et al. 2003), Trametes versicolor (Swamy and Ramsay 1999a, b; Borchert and Libra 2001; Martins et al. 2003), Pleurotus ostreatus (Shin et al. 1997; Rodrigues et al. 1999; Novotny et al. 2001), and Bjerkandera adusta (Heinfling et al. 1998; Heinfling-Weidtmann et al. 2001; Jarosz-Wilkołazka et al. 2002). In total, 20 fungal endophytes have been obtained from Melastoma malabathricum and examined for their potential to decolorize azo dyes such as congo red, methyl red, orange G, and an anthraquinone dye, Remazol Brilliant Blue R (RBBR ). Of these, the isolated Marasmius cladophyllus strain MS8 has decolorized RBBR , methyl red, congo red, and orange G in percentages of 97%, 56%, 48%, and 33%, respectively (Ngieng et al. 2013).

1.4 Biosorption and Bioaccumulation

Among all the methods for the treatment of wastewater, adsorption has been regarded as an efficient and low-cost process for the treatment of dyes mixed with effluents released by industry. The removal of textile dyes from wastewater using fungal biomass is an attractive option as it might reduce the overall cost of the treatment process (Saraf and Vaidya 2015). Biosorption is the combination of biomass solutes that cannot use any metabolic energy or transport in the binding process. This binding process may occur suddenly where live biomass is used. However, both living and dead biomass can be used in biosorption (Tobin et al. 1994).

The degradation of dyes has been mostly performed by microbial isolates originating from soils polluted with dyes, effluents from industry, or marine sources (Saratale et al. 2006; Abedin 2008; Gou et al. 2009). For instance, Kabbout and Taha (2014) studied the biosorption of methylene blue by the dead fungal biomass of Aspergillus fumigates and optimized the conditions for better absorption. Aspergillus niger and Rhizopus stolonifer showed the ability to remove dyes like Congo red and bromophenol blue respectively by biosorption (Fu and Viraraghavan 2001; Zeroual et al. 2006). Bayramoglu and Arica (2007) studied the native and heat-treated fungal biomass of Trametes versicolor for the removal of two benzidine dyes, direct red 128 and direct blue −1 using different parameters. The biosorption activity of the heat-treated and native biomass of T. versicolor was 152.3 and 101.1 mg/g for direct blue −1 and 225.4 and 189.7 mg/g for the removal of direct red. Iqbal and Saeed (2007) reported that the uptake efficiency of RBBR by immobilized Phanerochaete chrysosporium biomass in loofa sponge was much better than that of free fungal biomass with enhanced uptake efficiency of RBBR . The value of loofa sponge–immobilized biomass increased (18.6%) compared to free fungal biomass. Marcharchand and Ting (2017) showed that Trichoderma asperellum growing on fewer nutrients can retain its dye-decolorizing efficiency. Trichoderma asperellum has been grown in synthetic medium with different concentrations such as 20%, 50%, 75%, and 100%, and shown an ability to perform biosorption . This is also a good cost-effective strategy to use on fungi for dye removal; this method can help to lower the cost of cultivating the biomass of Ta for dye removal activities isolated at lower concentrations (20%, 50%, and 75%). This result demonstrated that lower nutrient levels might be useful in cultivating the biomass of Ta for dye removal activities (Marcharchand and Ting 2017) (Table 1.1).

Table 1.1 Biodegradation of various synthetic dyes by endophytic fungi
Full size table

However, endophytes associated with plants have been much less explored for their biosorbent activity. Ting et al. (2016) recovered an endophytic Diaporthe sp. fungus from Portulaca weed and explored it for its potential activity in biodegradation and biosorption in triphenylmethane (TPM) dyes. The live cells of Diaporthe sp. showed stronger decolorizing activity against malachite green, crystal violet, and methyl violet with decolorizing efficiencies (%) of 87.80%, 84.87%, and 78.81%, respectively. Additionally, Ting et al. (2016) reported that the decolorization of live cells is far better than the decolorizing efficiency (18.82%, 39.88%, 48.32%) of dead cells.

Bioaccumulation is explained as the accumulation of pollutants or any xenobiotic substance by actively growing cells by metabolism (Aksu and Donmez 2005). Aksu and Donmez (2005) suggested that some fungi, like Candida tropicalis, have the ability to remove different dyes like Remazol Black B and Remazol Blue using a bioaccumulation process. Similarly, Saccharomyces cerevisiae can remove dyes like Remazol Blue, Remazol Black B, and Remazol Red RB by bioaccumulation (Aksu 2003). Taskin and Erdel (2010) also showed the efficiency of fungi soilborne Aspergillus niger in decolorizing textile dye Reactive Black 5 through bioaccumulation.

1.5 Enzymes Involved in Biodegradation of Dyes

Lignin is easily degraded by most fungi owing to their extracellular secretion of nonspecific and nonselective enzymes. These enzymes are laccases , manganese peroxidases, and lignin peroxidases, which can work together to produce H2O2 and secondary metabolites. (Kirk and Farrell 1987; Levin et al. 2004). Similarly, due to their nonspecific mechanisms, these fungi are able to degrade lignin and various other pollutants such as PAHs, polychlorinated biphenyls, dioxins, chlorinated phenols, explosives, dyes, and pesticides (Pointing 2001). Some researchers have reported on the ability of laccases , manganese peroxidases, and lignin peroxidases to decolorize dyes (Cripps et al. 1990; Podgornik et al. 2001; Pointing 2001). Cha et al. (2001) reported that most fungi have cytochrome P-450 monooxygenase, which is involved in organic pollutant degradation.

Laccases are multicopper enzymes with the ability to oxidize phenolic and nonphenolic lignin-related compounds. Moreover, laccases have applications in bioremediation as well as other biotechnological applications (Yang et al. 2017). They are broadly distributed in fungi, bacteria, insects, and plants. They can catalyze the oxidation of a broad range of substrates, including mono-, di-, and polyphenols , ascorbate, and methoxyphenols through the concurrent reduction of oxygen to water. Most widely studied laccases are of fungal origin. They are primarily produced by ascomycetes, basidiomycetes, and deuteromycetes, of which white-rot basidiomycetes are regarded as the most proficient laccase producers (Arora and Sharma 2010; Si et al. 2013; Yang et al. 2017; Zhuo et al. 2017). Laccases are also commonly used in bleaching, pulping, dye decolorization, biosensing, food technology, and wastewater treatment (Campos et al. 2016). Endophytic fungi also have the potential to decolorize dyes discharged in various industries.

Laccases are among the major enzymes produced by endophytic fungi for decolorizing dye. Muthezhilan et al. (2014) reported on the fungal endophyte Fusarium sp. strain AEF17 isolated from the Ipomoea pescaprae plant showing laccase enzyme production. The laccase purified from this strain had the potential to decolorize nine different textile dyes. The maximum decolorization activity was found in blue M2R (BM2R), orange M2R(OM2R), and black-B (BB), followed by limited decolorization activity by red BSID (RBSID ), yellow MR(YMR ), blue MR (BMR ), magenta MP (MMP ), brown GR (BGR), and orange 3R (O3R) and decolorization. In another study, a fungal endophyte known as Myrothecium verrucaria was isolated from pigeon pea that has the potential to produce laccase enzyme. In the presence of ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate), the isolate Myrothecium verrucaria exhibited significant decolorization potential toward methyl orange, Congo red, crystal violet, and methyl red) (Sun et al. 2017). Endophytic fungi Phlebia spp. isolated from P. hispidum Sw. and P. formosus, obtained from H. annuus L., were active in biodegradation of textile dyes. They displayed the ability to degrade Reactive Black 5 and Reactive Blue 19 textile dyes. After 30 days of treatment, isolated Phlebia spp. and P. formosus showed 90% and 70% degradation of black and blue dye, respectively. Phlebia spp. showed the highest production of extracellular laccase, which suggests a role of the enzyme in the decolorization of the blue and black textile dyes (Bulla et al. 2017). The strain Ganoderma cupreum AG-1 isolated from decayed wood showed the potential to produce lignolytic enzymes and the capacity to decolorize around 19 different azo dyes in a pH range of 4.5–6. The Ganoderma cupreum strain AG-1 was also found to produce laccase and manganese peroxidase . G. cupreum AG-1 showed a capacity to produce large amounts of laccase, which indicates its role in decolorizing dyes (Gahlout et al. 2013). A white-rot fungis from Argentina, Coriolus versicolor f. antarcticus, showed potential for the production of various extracellular enzymes like laccase, lignin peroxidase, and manganese peroxidase on solid medium, which have the ability to decolorize different dyes such as malachite green, azure B, poly R478, anthraquinone blue, Congo red, and xylidine (Levin et al. 2004). Levin et al. (2004) suggested that the strain Coriolus versicolor f. antarcticus could be used as a candidate in biodecoloration processes. Fungal endophytes associated with Melastoma malabathricum exhibited the ability to decolorize three azo dyes: methyl red, Congo red, and orange G. Among all the endophytic isolates recovered from M. malabathricum, a basidiomycete fungus, Marasmius cladophyllus, decolorized 97% of RBBR dye, followed by 56% decolorization of methyl red (Table 1.1).

1.6 Conclusion

Fungus-mediated biodegradation or removal of dye from wastewater involves either the use of pure enzymes or biosorption . This chapter discussed the importance of endophytic fungi in both biosorption and enzyme-mediated removal of dyes using endophytic fungi.

Laccases from endophytic fungi have demonstrated their potential in degrading various types of dyes. Additionally, many studies on fungal biosorbents have suggested that biosorbents represent an emerging and promising solution to conventional practices. Fungal endophytes have been much less explored for their ability to remove dyes using a biosorption approach. However, many studies have reported on purified laccases from endophytic fungi for their potent activity in degrading dyes. Nevertheless, it is essential to search for endophytic fungal strains that are very eco-friendly and nontoxic that can degrade various dyes easily.