Effects of Natural Metabolites from Fungi, Bacteria, and Plants on the Degradation of Polycyclic Aromatic Hydrocarbons by Pleurotus ostreatus var. Florida.

Abstract

Background: Ligninolytic fungi are promising organisms in developing bioremediation technologies due to their ability to degrade various pollutants. Fungi and their extracellular enzymes in soil inevitably collide with metabolites produced by other organisms. Here, we investigated the effect of some natural metabolites on the degradation of a model mixture of polycyclic aromatic hydrocarbons (PAHs) by the fungus Pleurotus ostreatus var. Florida.

Methods: Fungus was grown in the liquid medium containing PAHs with or without the addition of natural metabolites. The degraded PAHs and the identification of metabolites were checked using high-performance liquid chromatography (HPLC). Enzymatic activities were measured spectrophotometrically using test substrates. The metabolite effects on the pure laccase and versatile peroxidase were also checked. All experimental treatments were analyzed using Excel 2019 (Microsoft Office 2019, USA).

Results: Indole-3-acetic acid (IAA) and salicylic acid increased PAH degradation by 25-70%. However, tryptophan, a precursor to IAA biosynthesis, slightly increased the degradation of only three-ring PAHs. The tested flavonoids reduced the PAH degradations, which may have resulted from the inhibition of mycelial growth by these compounds. Ferulic and cinnamic acids, precursors to lignin biosynthesis, also inhibited PAH degradation. Of the tested fungal metabolites, only veratryl alcohol promoted PAH degradation: the four-ring PAHs became more accessible to fungal degradation (43.5 and 38.1% for fluoranthene and pyrene, respectively). Oxalic and malonic acids, the most actively produced fungal organic acids, reduced the degradation of all PAHs but fluoranthene. HPLC led us to identify 9,10-phenanthrenequinone, 9,10-anthraquinone, and 9-fluorenone as the main metabolites of PAH degradation. P. ostreatus is a strong producer of extracellular laccases and peroxidases, whose involvement in PAH degradation is also well known. In our study, the most vigorous laccase inducers were tryptophan and ferulic acid (40 and 60%, respectively), whereas IAA and salicylic acid were weaker inducers (about 20%). Ferulic and salicylic acids increased versatile peroxidase activity by 1.5-2 times, whereas other effectors reduced it to varying degrees.

Conclusions: These results are important for developing environmental biotechnologies that combine phyto- and mycoremediation.