98

Bioremediation for Sustainable Environmental Cleanup

(Deshmukh et al. 2016). VPs also fall in this peroxidase isozymes family, capable to operate on

a number of substrates. Several scientific reports have been documented regarding the PAHs

degradation by fungal peroxidases.

6.3.1.1.2.1 Manganese peroxidase

Manganese peroxidases are the heme peroxidase, principally oxidize the Mn²⁺ ions that persist

within the xenobiotic compounds such as PAHs, into Mn³⁺ which is an extra reactive form and

fixed by fungal chelator, i.e., oxalic acids. Though, Mn³⁺ performs as a low molecular weight

molecule that functions as a soluble redox mediator, which disintegrates both the phenolic and

nonphenolic contaminants and generates free radicals that have the propensity to break reluctantly.

Structurally, MnPs are comprised of two α-helices with haem in between them, two Ca²⁺ ions, and

five disulfide bridges (Sutherland 1992). MnP has pronounced industrial applications viz, beverage,

biofuel, pulp and paper, textile and food industries in addition to PAHs degradation (Karigar and

Rao 2011, Chowdhary et al. 2019). An example of such fungal MnP-mediated PAHs degradation

was documented from I. lacteus, where the experimented PAHs were ANTH and PYR (Kadri

et al. 2017). Another example of WRF is G. lucidum, which can produce 47,444 UL^–1 and 50,977 of

MnP for the degradation of 99.65 and 99.58% of 20 mg L^–1 PHE and PYR, respectively (Agrawal

et al. 2018). In addition to this, 7.21 U g^–1 MnP production was also observed from a WRF Agrocybe

aegerita for the mineralization of 50 mM fluorene (FLR), PYR, CHY and B(a)P (Vipotnik et al.

2021). Further, Trametes sp. is a WRF that can degrade a significant amount of FLR, FLU, PYR,

PHE and ANTH mixture with 69.7 UL^–1 of MnP production (Zhang et al. 2016).

6.3.1.1.2.2 Lignin peroxidase

Lignin peroxidases of fungal origin can oxidize most PAHs and requires manganese and hydrogen

peroxide to function. Generally, LiP can oxidize a number of phenolic and nonphenolic substances.

Such LiP has two locations for Ca²⁺ binding and glycosylation and in addition to that have four

disulfide bridges. All these integral conformations sustain the enzyme’s 3-D structure. Eight minor

and major-helices, structured into two domains, make up the globular configuration of LiPs, which

contains the active center. This active center constitutes the haem-chelater: ferric ion. Due to its

higher redox potential, LiPs can oxidize compounds that other peroxidases are unable to oxidize.

Several steps are involved in each catalytic cycle of LiPs. Firstly, H2O2 produces a radical cation as

an intermediate by oxidizing the native enzyme known as ferryloxo porphyrin. Subsequently, the

first step succeeds by a pair of single electron reduction stages by an electron donor compounds,

i.e., veratryl alcohol to generate an intermediate complex as well as a radical cation. Now,

oxidation of another veratryl alcohol molecule occurs through such a transient composite and

thereafter the transient composite converts to its native state to begin a new catalytic cycle of LiP

(Sigoillot et al. 2012, Wong 2009, Choinowski et al. 1999). Additionally, LiP has a non-specific type

of mechanism toward the substrates. One such example is ANTH bioremediation by utilizing LiP

of P. chrysosporium with metabolites like 9,10-anthraquinone and phthalic, illustrated in Figure 6.6

(Pozdnyakova 2012). In another instance, G. lucidum, a member of WRF can produce 3613 UL^–1

and 3283 UL^–1 of LiP, which is responsible for 99.65 and 99.58% mineralization of 20 mg L^–1 PHE

and PYR, respectively (Agrawal et al. 2018). Further, 85.9% remediation potentiality with 2419

UL^–1 LiP production was also observed from Fusarium sp. in response to the 5 mg L^–1 mixture of

HMW-PAHs [FLU, PYR, B(a)A, CHY, B(b)F, B(k)F, B(a)P, dibenzo(a,h)anthracene, benzo(g,hi)

perylene and indeno(1,2,3-cd)pyrene] (Zhang et al. 2020). Interestingly, 2.24 ± 0.09 Ug^–1 and

2.08 ± 0.04 Ug^–1 of LiP production from A. aegerita was documented with 85.62 and 85.% FLR,

83.64 and 80.42% PYR, 79.24 and 60.32% CHY, 80 and 85.74% B(a)P degradation when treated

with kiwi peels and peanut shells on solid state fermentation condition, respectively (Vipotnik

et al. 2021). In a recent study, Omoni et al. (2022) demonstrated that 2.00 Ug^–1 and 1.10 Ug^–1

of LiP production were achieved by the WRF P. chrysosporium and P. ostreatus for utmost PHE

degradation.