Polycyclic aromatic hydrocarbons (PAHs) are a large group of chemicals. They represent an important concern due to their widespread distribution in the environment, their resistance to biodegradation, their potential to bioaccumulate and their harmful effects. Several pilot treatments have been implemented to prevent economic consequences and deterioration of soil and water quality. As a promising option, fungal enzymes are regarded as a powerful choice for degradation of PAHs. Phanerochaete chrysosporium, Pleurotus ostreatus and Bjerkandera adusta are most commonly used for the degradation of such compounds due to their production of ligninolytic enzymes such as lignin peroxidase, manganese peroxidase and laccase. The rate of biodegradation depends on many culture conditions, such as temperature, oxygen, accessibility of nutrients and agitated or shallow culture. Moreover, the addition of biosurfactants can strongly modify the enzyme activity. The removal of PAHs is dependent on the ionization potential. The study of the kinetics is not completely comprehended, and it becomes more challenging when fungi are applied for bioremediation. Degradation studies in soil are much more complicated than liquid cultures because of the heterogeneity of soil, thus, many factors should be considered when studying soil bioremediation, such as desorption and bioavailability of PAHs. Different degradation pathways can be suggested. The peroxidases are heme-containing enzymes having common catalytic cycles. One molecule of hydrogen peroxide oxidizes the resting enzyme withdrawing two electrons. Subsequently, the peroxidase is reduced back in two steps of one electron oxidation. Laccases are copper-containing oxidases. They reduce molecular oxygen to water and oxidize phenolic compounds.

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Biodegradation of polycyclic aromatic hydrocarbons (PAHs) by fungal enzymes: A review.

Principles of microbial degradation of petroleum hydrocarbons in the environment

• Under cadmium (Cd) stress, Solanum nigrum accumulated threefold more Cd in its leaves and was tolerant to Cd, whereas its low Cd-accumulating relative, Solanum torvum, suffered reduced growth and marked oxidative damage. However, the physiological mechanisms that are responsible for differential Cd accumulation and tolerance between the two Solanum species are largely unknown. • Here, the involvement of antioxidative capacity and the accumulation of organic and amino acids in response to Cd stress in the two Solanum species were assessed. • Solanum nigrum contains higher antioxidative capacity than does S. torvum under Cd toxicity. Metabolomics analysis indicated that Cd treatment also markedly increased the production of several organic and amino acids in S. nigrum. Pretreatment with proline and histidine increased Cd accumulation; moreover, pretreatment with citric acid increased Cd accumulation in leaves but decreased Cd accumulation in roots, which indicates that its biosynthesis could be linked to Cd long-distance transport and accumulation in leaves. • Our data provide novel metabolite evidence regarding the enhancement of citric acid and amino acid biosynthesis in Cd-treated S. nigrum, support the role of these metabolites in improving Cd tolerance and accumulation, and may help to provide a better understanding of stress adaptation in other Solanum species.

Comparative physiological responses of Solanum nigrum and Solanum torvum to cadmium stress

Kun Wu

Papers

Mechanisms of Cd and Cr removal and tolerance by macrofungus Pleurotus ostreatus HAU-2.

Improvement of tolerance to lead by filamentous fungus Pleurotus ostreatus HAU-2 and its oxidative responses.

Contrasting characteristics of anthracene and pyrene degradation by wood rot fungus Pycnoporus sanguineus H1

Diversity of phenanthrene and benz[a]anthracene metabolic pathways in white rot fungus Pycnoporus sanguineus 14