Phthalate esters (PEs) – the esters of 1,2-benzenedicarboxylic (phthalic) acid – are the most commonly used plasticizers worldwide. Currently, there is an ever-growing concern about persistence, ubiquity and toxicity of PEs. Structurally resembling estrogen, PEs can potentially act as endocrine disrupting chemicals adversely affecting development and reproduction. A promising approach of PEs degradation is their biotranformation by fungal enzymes. The aim of this work is to study the biodegradation of diethyl phthalate (DEP) and dibutyl phthalate (DBP) by white rot fungi from different taxonomic and ecophysiological groups.
The selected fungi were: Trametes hirsuta – the primary colonizer on lignum; Steccherinum ochraceum and Peniophora lycii – the secondary colonizers on lignum; Crucibulum leave – the stramentum colonizer; and Agrocybe praecox – the humus colonizer. The overall oxidase activity and growth inhibition were assessed on malt agar plates containing 0.5, 1.0, and 1.5 g*L^-1 of DEP/DBP.
For biotransformation of phthalates fungal biomass was grown by a submerged method on a glucose-peptone medium. When the maximum biomass was accumulated, the mycelium was transferred to a medium of the same composition with peptone replaced by NaNO₃ and 1 g*L^-1 of phthalates. The samples were taken on days 3, 6, 10, and 14, and PEs were extracted with dichloromethane. The content of DEP and DBP in the extracts was estimated by a thin layer chromatography.
The decrease in the fungal growth rate on an agar medium containing phthalates has been shown. The growth inhibition by DEP was higher than by DBP. Only T. hirsuta and P. lycii were able to grow on a medium with a 1.5 g*L^-1 concentration of DEP. An increase in oxidase activity was shown during the growth on the DEP-containing medium for T. hirsuta and P. lycii, and on a DBP-containing medium – for C. leave, compared with control media without phthalates. T. hirsuta, P. lycii and C. leave completely degraded DBP within 10 days. The rate of DEP destruction by T. hirsuta and P. lycii was significantly lower than that of DBP. This correlated with the growth rate of these fungi on the solid agar media containing corresponding phthalates.
Thus, it was shown that white rot fungi are capable of degradation of phthalates. The effectiveness of biodegradation most probably depends on the enzymatic system of a particular species. The results of this work can be used for development of a phthalate biodegradation technology.