Biodegradation of Xenobiotics in Soil by Fungi

Any substance foreign to a biological system is known as xenobiotic compound. The manufacturing and processing of xenobiotic chemicals on the large scale have led to serious surface and subsurface soil contamination. Biotransformation of the hazardous pollutants to less toxic substances or their complete mineralization represents an economical substitute to clean up soil and water. In principle, fungi by virtue of their enzymes can biodegrade any naturally existing biopolymers and some of the synthetic polymers as well. Degradation of polymers largely depends on the fungal extracellular enzymes, namely, oxidoreductases and hydrolases. White-rot ligninolytic fungal strains such as T. versicolor and P. ostreatus have been recognized to be the major decomposers of biopolymers via laccase-mediated transformation. Moreover, the ligninolytic fungal strains carrying enzyme Mn-peroxidase activity demonstrated the maximum degradation of naphthalene (69 %). Many non-ligninolytic species degrade polycyclic aromatic hydrocarbons (PAHs) via cytochrome P450 monooxygenase and epoxide hydrolase-catalyzed reactions to form transdihydrodiols. Remediation of nitro-aromatics along with their recalcitrant carcinogenic intermediates, possessing the worst degree of toxicity hazardous rating 3, has been described by utilizing fungal species such as Phanerochaete chrysosporium or Pseudomonas sp. ST53. Additionally, white-rot fungi possessing oxidative enzymes have the ability of TNT degradation and mineralization to CO2. On the other hand, fungal laccases have been reported to catalyze the transformation of the model endocrine disruptors, alkylphenols and biphenyls. For instance, T. versicolor catalyzed the partial transformation of nonylphenol into carbon dioxide. Discovering the new beneficial fungal strains in addition to isolation, engineering, and sequencing of new useful enzymes is highly desirable to further strengthen the biodegradation of contaminated soil.