Recent advances in applications of acidophilic fungal 2 microbes for biochemicals 3

The processing of fossil fuels is the major environmental issue today which should be 10 lessen. Biomass is gaining much interest these days as an alternate to energy generation. 11 Lignocellulosic biomass (cellulose, hemicellulose and lignin) is abundant and has been used for a 12 variety of purposes. Among them, the lignin polymer having phenyl-propanoid subunits linked 13 together through C-C bonds or ether linkages, can produce numerous chemicals. It can be 14 depolymerized by microbial activity together with certain enzymes (laccases and peroxidases). Both 15 acetic acid and formic acid production by certain fungi contribute significantly to lignin 16 depolymerization. Natural organic acids production by fungi has many key roles in nature that are 17 strictly dependent upon organic acid producing fungus type. Fungal enzymatic conversion of 18 lignocellulosic is beneficial over other physiochemical processes. Laccases, the copper containing 19 proteins oxidize a broad spectrum of inorganic as well as organic compounds but most specifically 20 phenolic compounds by radical catalyzed mechanism. Similarly, lignin peroxidases (LiP), the heme 21 containing proteins perform a vital part in oxidizing a wide variety of aromatic compounds with 22 H2O2. Lignin depolymerization yields value-added compounds, the important ones are BTX 23 (Benzene, Xylene and Toluene) and phenols as well as certain polymers like polyurethane and 24 carbon fibers. Thus, this review will provide a concept that biological modifications of lignin using 25 acidophilic microbes can generate certain value added and environment friendly chemicals. 26


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The processing as well as the withdrawal of fossil fuels are the major prevailing environmental 30 issues these days. Therefore, it is the utmost need of the time to lessen fossil fuels consumption as 31 much as possible. The only reliable solution to this major issue is to exchange the petroleum products 32 with lesser costly and environmental friendly (green) chemicals. Over 10 million tons of 33 petrochemical materials (phenol and its derivatives) are generated annually. Thus, advancement is

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The production of enzymes has been improved by some specific compounds which act as

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Laccases are multi-copper proteins that are characterized by their electron paramagnetic 211 resonance (EPR) spectrum in three distinctive types:

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 Type-1 copper: attach to two amino acids (cysteine and methionine) and two histidine 213 ligands, because of these enzymes show blue color.

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 Type-2 copper: attach via water and two histidine ligands.

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The catalytic activity is generally dependent on three binding sites with these four types of copper 219 ions. Type-1 copper is the main primary electron acceptor and then electron transferred to the tri-220 nuclear cluster. The oxygen reduction into water also takes place on these binding sites. Laccases 221 remove solely one electron to oxidize its substrate and laccase with its total reduced state contain four 222 electrons consequently electrons gain by oxygen yielding water [88]. Substrate spontaneously forms 223 free radical or a new compound after the removal of proton (Fig. 6)

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A large body of literature has explained ABTS application of lignin degradation using laccase.

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The use of mediators, most probably ABTS is unique for the oxidation of lignin subunits. Many coupled with laccase enhance the catalytic activity of laccase to generate lignin subunits having an 262 average weight of 5300 g/mol [93]. The mechanism of ABTS oxidation indicates that ABTS 2+ di-cation only act as an intermediate, for oxidation of non-phenolic structures. Conversely, ABTS + -cation described the effects of mediators and laccase enzyme on lignin model compounds to fully recognize 267 the laccase reaction owing to the lignin structure complexity [93] (Fig. 8).

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Lignin can be depolymerized into various aromatic components. As these compounds are 372 obtained from lignin, the first and the foremost duty is to eradicate the oxygen containing functional 373 groups by decarboxylation, decarbonylation, dehydroxylation and demethoxylation [123]. Benzene 374 is a resourceful petrochemical building block from which more than 250 products could be formed.