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Bioremediation for Sustainable Environmental Cleanup

soluble and non-hazardous when compared with their parental PAHs compounds, hence lowering

health-risk. C. elegans exhibit a sulfur addition process in which naphthalene (NAP) and ANTH are

converted into 1-naphthyl and 1-anthryl sulfate metabolites, respectively (Lisowska and Długoński

2003). On the other hand, enhancement in PAHs degradation by accelerating the PAHs solubility

can be achieved by conjugation process. P. chrysosporium shows glucose as PAHs conjugates.

According to Sutherland (1992), 7,12-dimethylbenzanthracene can be biotransformed by C. elegans

producing trans-3,4-dihydrodiol metabolites. It can be further metabolized into phenol carried out

by Mucor sp., P. chrysogenum. S. racemosum biosystem via conjugating with glucuronic acid.

ANTH biodegradation can be accomplished by various fungi such as Fusarium sp., Aspergillus sp.,

Penicillium sp., Trichoderma sp., Ulocladium chartarum and Absidia cylindrospora (Giraud et al.

2001). In addition to this, the non-ligninolytic fungi involved in pherenthrene metabolism usually

belong to Alternaria sp., F. culmorum, P. janczewskii, C. elegans, Cladosporium herbarum and

T. hamatum, etc. (Schmidt et al. 2010).

6.3.1.2.1 Cytochrome P450

Cytochrome P450 monooxygenase is a heme thiolate intra-cellular biocatalyst produced by

various species of fungi and bacteria. Usually, CYP450 accomplishes as terminal monooxygenases

which catalyze a wide range of biochemical reactions such as carbon hydroxylations, heteroatom­

oxygenations, dealkylations, epoxidations, reductions and dehalogenations (Bernhardt 2006).

Phenomenal eukaryotic Cytochrome P450 systems consist of P450 monooxygenase and P450

oxidoreductase and both these are typically membrane-associated (Zhuo and Fan 2021). WRF has

employed P450 monooxygenase systems for the oxidative decontamination and eradication of

several xenobiotic compounds, especially various organic pollutants like PAHs. It helps in converting

water-insoluble compounds into water-soluble compounds and cleaves the organic pollutants by

incorporating molecular oxygen. Most of the non-ligninolytic fungi can secrete this class of enzyme.

Examples of CYP450 producing fungi are P. chrysosporium, Cochliobolus lunatus and A. niger

which are evidenced by the bioremediation of PAHs. A significant amount (up to 89%) of B(a)P

degradation by the WRF P. chrysosporium has also been documented (Bhattacharya et al. 2013).

PHE degradation via cytochrome P450 system of P. sanguineus was also observed by Li et al.

(2018). Multiple PAH degrading capability and their transformation from PYR to 1-hydroxypyrene;

PHE to 3-phenanthrol, 4-phenanthrol, 9-phenanthrol; and B(a)P to 3-hydroxy B(a)P by the activity

of cytochrome P450 from P. chrysosporium has also been reported (Syed et al. 2010). Further,

Syed et al. (2011 and 2013) reported HMW-PAH degradation by the similar enzymatic potentiality

of P. chrysosporium. In addition to that, the conversion of PHE to phenanthrene trans-9,10­

dihydrodiol was shown by the P. chrysosporium with its same enzymatic activities (Ning et al.

2010). Ostrem Loss et al. (2019) investigated that PHE was bioremediated by the non-ligninolytic

fungi, P. chrysosporium, by utilizing CYP450 as the key enzyme. Despite the fungal origin,

researchers explored the enhanced CYP450 production by the development of recombinant strain

and subsequently gene expression in white-rot fungus in response to HMW-PAHs; for example,

the expression of genes CYP450-pc-1 and CYP450-pc-2 in P. chrysosporium (Lin et al. 2022). In

another study, the recombinant strain CYP63A2 of P. chrysosporium revealed ameliorated oxidation

capacity towards HMW-PAHs (Syed et al. 2013).

6.4 Production of Biosurfactants

Recent bioremediation studies emphasize on the use of biosurfactants having a microbial origin that

have attributed to the mineralization of PAHs in the environment (Guo and Wen 2021, Mekwichai

et al. 2020, Karlapudi et al. 2018). Greater biodegradable potentiality, lower toxicity, foam

formation and eco-sustainable nature of biosurfactants promote their application in the remediation

of PAHs over chemical surfactants (Pi et al. 2017). Microbial biosurfactants are surface-active