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Bioremediation for Sustainable Environmental Cleanup

Figure 6.4. B(a)P mineralization by P. chrysosporium, C. elegans, A. ochraceus, T. versicolor and P. cinnabarinus

(Majcherczyk et al. 1998, Datta and Samanta 1988, Haemmerli et al. 1986, Cerniglia and Gibson 1980).

consortia of P. ostreatus with Penicillium chrysogenum by 86.15% removal rate and P. ostreatus with

Pseudomonas aeruginosa by 75.1% removal rate, whereas P. ostreatus PO-3 only remediated 64.3%.

On the other hand, the ligninolytic fungi or the WRF are known for their magnificent PAHs­

degrading abilities with their potential intra and extracellular enzymes. In WRF mediated PAHs

remediation process, PAHs oxidation begins with the formation of dihydrodiol by a multi-component

dioxygenase enzyme system which further undergoes ortho or meta ring cleavage pathways and

produces metabolites such as catechol and protocatechuate (Sipilä et al. 2010). Furthermore, some

fungi undergo more extensive PAH decomposition, leading to the breakdown of the benzenoid rings

and the release of CO2. Enzymes involved in WRF-mediated PAHs breakdown mainly belong to the

LiP, laccase, MnP and VP (Gupta and Pathak 2020). The mechanisms involved in PAHs degradation

by both ligninolytic and non-ligninolytic fungi have been depicted in Figure 6.5.

6.3.1.1.1 Laccase

Extracellular enzymes, especially laccase, are crucial features that contribute to PAHs cleanup.

Laccases are benzenediol: oxygen oxidoreductases and are metalloproteins in nature, which belong

to the polyphenol oxidases and consist of four copper atoms of altered types in their catalytic site

(Baldrian 2006). Laccases are one of the key ligninolytic biomolecules that oxidize a broad range of

aromatic compounds holding phenolic moieties, benzenothiols, aromatic amines and hydroxylindols

(Dhagat and Jujjavarapu 2022). Such enzymes utilize the molecular oxygen as an electron acceptor

and organic or inorganic metal complexes as substrates (Zimmerman et al. 2008). Additionally,

laccases use oxygen as an oxidizing agent and reduce it into water molecules (Tavares et al.

2006). Laccases are produced by diversified living systems like plants, fungi, bacteria and insects

(Show et al. 2022). Among microbes, laccases of bacterial origin are reported from some potent