To adapt to abiotic and biotic stressors, endophytic microbes produce bioactive substances (Guo et al. 2008). Endophytic fungi produce different kinds of extracellular enzymes viz. hydrolases, lyases, oxidoreductases and (Traving et al. 2015).
Biotechnological Applications of Endophytic Fungi
Bioresources of Hydrolytic Enzymes
- Cellulases
- Xylanase
- Lipase
- β -glucosidase
- Tannases
- Pectinases
- Phytases
- Ligninolytic Enzymes
Tasia et Melliawati (2017) inventa Acremonium sp. et classis Coelomycetes pro effectoribus xylanasis esse. Studio per Marques et al. 2018 Acremonium sp., Botryosphaeria sp., Chaetomium sp., Cladosporium cladosporioides, Colletotrichum crassipes, Coniella petrakii, Coniothyrium minitans, Myrothecium gramineum, Paecilomyces sp., Phomopsis stipata vir., Sacchariidercola sp.
Bioresources for Secondary Metabolites
- Azadirachtin
- Camptothecin
- Taxol
- Gibberellic Acid and Indole Acetic Acid
- Siderophores
Azadirachtin acts as an antifeedant, insect growth regulator and sterilant in insects (Jennifer Mordue et al. 1998). Azadirachtin A and its various congeners have significant biological activity, particularly insecticidal and nematicidal (Klenk et al. 1986). The bark of the tree was extensively used in traditional Chinese medicine (Wall et al. 1966).
In plants, the synthesis of taxol occurs with the inclusion of three genes, namely ts (involved in the formation of the taxane framework), dbat (involved in the formation of bacatin-III) and bapt (involved in the formation of the phenylpropanoyl side chain at C -13) (Xiong et al. 2013). Recently, Xiong et al. 2013) revealed that in three taxol-synthesizing endophytes isolated from Anglo-Japanese yew or T. The biosynthetic pathway of gibberellic acid (GA) was compared with other secondary metabolites (Kumara et al. 2014).
Endophytic microorganisms have been found to produce phytohormones such as GA, abscisic acid, auxins, cytokinins and ethylene (Kaul et al. 2013). However, fungal endophytes promote plant growth through the production of ammonia and plant hormones, especially IAA (Bal et al. 2013). Endophytes help plants take up dissolved phosphate (Wakelin et al. 2004), promoting hyphae growth and mycorrhizal colonization (Will and Sylvia 1990), and by producing siderophores (iron chelating molecules that increase phosphate availability for plants) (Costa and Loper 1994).
Pharmaceutically Important Bioactive Compounds
The potential of biofertilizers was formulated using endophytic bacteria for increased banana production in a sustainable manner (Ngamau et al. 2014). 2011) reported that the endophytic fungus of Tinospora crispa (L.) was a potential candidate for the synthesis of bioactive compounds. Hypericin isolated from fungal endophytes of medicinal plants possesses antimicrobial activity against Staphylococcus sp., Klebsiella pneumoniae, Pseudomonas aeroginosa, Salmonella enteric and Escherichia coli (Kusari and Spiteller a) reported five fungal endophytes isolated from annumiscum, Capp. .
Buds and leaves of Malabar Embelia, found in peninsular India, were subjected to the isolation of fungal endophytes. Four different fungal endophytes, Cladosporium cladosporiodes, Penicillium sp., Aspergillus niger and Alternaria sp., were identified and characterized for phytochemical analysis and antibacterial activity against Pseudomonas aeuroginosa, Bacillus subtilis and Shigella flexneri. The four different fungal endophytes showed the presence of phytochemicals in different concentrations: cardiac glycoside, flavonoids, phenols, tannins, terpenoids, cardenolides and saponins.
Endophytic microbes are a major source of bioactive compounds to meet the requirements of the pharmaceutical and medical industries (Chandrappa et al. 2013). 2014) isolated 193 endophytic microbes from Chinese medicinal plants, Camptotheca cuminata Decne, Gastrodia elata Blume and Pinellia ternata. Based on morphological and rDNA sequences, the fungal isolates belong to Ascomycota, Basidiomycota and Mucoromycotina.
Lignocellulosic Biorefineries: Biofuel Production
A variety of extracellular oxidative enzymes are produced by white-rot fungi (basidiomycetes), as they are the main wood rotters that synergistically and efficiently degrade lignin. Based on macroscopic characteristics, wood-rotting basidiomycetes are categorized into white-rot and brown-rot fungi (Schwarze et al. 2000). Pleurotus eryngii was reported to produce versatile peroxidase showing catalytic properties similar to LiP and MnP (Ruiz-Dueñas et al. 1999).
Other extracellular enzymes involved in wood lignin degradation are H2O2-generating oxidases, aryl-alcohol oxidase (AAO), glyoxal oxidase, aryl-alcohol dehydrogenases (AAD) and quinone reductases (QR) (Guillén et al. 1997; Guillén et al. Gutierrez; 1994). First discovered in Phanerochaete chrysosporium, this enzyme is a heme peroxidase with an extremely high redox potential and low pH optimum (Tien 1987). Laccase enzymes produced by endophytic fungi have a broad substrate specificity and generally act on small organic substrates, such as polyphenols, methoxy-substituted phenols, and aromatic amines.
Fungal laccases are used in paper production for delignification, bioremediation of phenolic compounds and biobleaching (Kunamneni et al. 2008). Exoglucanases, endoglucanases, β-glycosidases, exoxylanases and endoxylanases, and β-xylosidases are the main hydrolytic enzymes involved in lignocellulose degradation (Van Dyk and Pletschke 2012). Laccases, MnP and LiP (oxidative enzymes) and additional hemicelluloses (e.g. acetyl esterase, b-glucuronidase, endo-1, 4-β-mannanase and α-galactosidase) and oxidoreductases (aryl-alcohol-oxidase) are needed for complete degradation of lignocellulosic materials. , glucose-1-oxidase, glyoxal-oxidase and pyranose-2-oxidase) are required (Correa et al. 2014).
Endophytic Fungi in Bioremediation
To inhibit the growth of endophytes, the plant synthesizes a series of metabolites and toxic endophytes during a period of co-evolution, progressively establishing a genetic system as a tolerance mechanism generating exoenzymes and mycotoxins (Mucciarelli et al. 2007; Pinto et al. .2000). Fungal endophytes that synthesize enzymes degrade macromolecules into simpler compounds, including amylases, lipases, pectinase, cellulase, proteinase, phenol oxidase and lignin catabolic enzymes (Oses et al. In general, fungal endophytes have been declared the ability to use compounds various organics, such as glucose, oligosaccharides, cellulose, hemicelluloses, lignin, keratin, pectin, lipids and proteins, allowing the degradation of structural components into simpler forms (Kudanga and Mwenje 2005; Tomita.3etair 200; 2003).
One of the methodologies in which green plants are used for the bioremediation process is called phytoremediation. Many studies have shown that endophytes produce various enzymes to degrade organic contaminants and reduce phytotoxicity and evapotranspiration of volatile contaminants (Li et al. 2012b). 2010) reported that the infection of Festuca pratensis and Festuca arundinacea, two species of grasses, by two endophytic fungi, Neotyphodium coenophialum and Neotyphodium uncinatum, increased the ability of plants to accumulate more Cd in roots and shoots and in addition reduced plant stress. increase in biomass production. In heavy metal-contaminated habitats, microorganisms are known to alter various detoxification mechanisms such as biosorption, bioaccumulation, biotransformation, and biomineralization (Gadd 2000; Lim et al. 2003; Malik 2004).
The endophytic fungus Phomopsis sp. VA-35), obtained from Viguiera arenaria, was reported to biotransform the tetrahydrofuran lignan, (-)-grandisin, into a novel compound, 3,4-dimethyl-2-(4'-hydroxy-3',5' -dimethoxyphenyl)-5-methoxytetrahydrofuran (Verza et al. 2009). Aminophenol was formed as an important intermediate during the metabolic pathway for the degradation of HBOA and BOA (Zikmundova et al. 2002). Based on 18S rRNA gene sequencing, it was reported that Lasiodiplodia theobromae, isolated from the leaves of Boswellia ovalifoliolata, an endemic medicinal plant of Tirumala Hills, showed resistance to all four heavy metals, Co, Cd, Cu and Zn, up to 600 ppm (Sani et al. 2017).
Endophytic Fungi in Agriculture
In another study, the endophytic fungi Fusarium sambucinum, Plectosporium tabacinum, Gliocladium cibotii and Chaetosphaeria sp., isolated from the roots and shoots of Aphelandra tetragona, were able to transform the benzoxazi-nones 2-benzoxazoline (BOhydroxyone) and -1,4- benzoxazin-3-one (HBOA). Based on 18S rRNA gene sequencing, Lasiodiplodia theobromae isolated from the leaves of Boswellia ovalifoliolata, an endemic medicinal plant from Tirumala Hills, was reported to show resistance to all four heavy metals, Co, Cd, Cu and Zn, up to 600 ppm (Sani et al. 2017). available, producing auxins, cytokinins, gibberellins, siderophores, ammonia, HCN and various hydrolytic enzymes, and ultimately promoting the growth of host plants. 2014) studied the growth promotion potential of Phoma sp. isolated from Tinospora cordifolia and Calotropis procera for maize.
In the study of Rinu et al. 2014), Trichoderma gamsii, isolated from the lateral roots of lentils with diverse plant growth promoting properties, demonstrated its potential in promoting plant growth under greenhouse conditions using two grains and two legumes, suggesting that the potential It can be developed as a bioformulation for application under a mountain ecosystem. 2017) investigated the effect of Penicillium simplicissimum, Leptosphaeria sp., Talaromyces flavus and Acremonium sp. In the study of Asaf et al. 2018), Aspergillus flavus CHS1, an endophytic fungus isolated from the roots of Chenopodium album with multiple growth-promoting activities, was tested for its ability to promote the growth of mutant Waito-C rice. In addition, the strain was used to evaluate its potential to improve soybean growth under salt stress.
2018) evaluated whether the colonization of two fungal endophytes isolated from wild Nicotiana species from areas of drought-prone northern Australia, and a plant virus, yellowtail flower soft spot virus, could improve water stress tolerance in N. Fungal endophyte communities associated with plants play an important role in balancing the ecosystem and in promoting the growth of hosts. Fungal endophytes are therefore receiving greater attention and are of greater interest to chemists, ecologists and microbiologists as a treasure trove of biological resources, due to their diverse vital roles in the ecosystem.
Future Prospects and Conclusion
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