Abstract
Phthalate esters (PEs, Phthalates) are environmentally ubiquitous as a result of their extensive use as plasticizers and additives in diverse consumer products. Considerable concern relates to their reported xenoestrogenicity and consequently, microbial-based attenuation of environmental PE concentrations is of interest to combat harmful downstream effects. Fungal PE catabolism has received less attention than that by bacteria, and particularly fungi dwelling within aquatic environments remain largely overlooked in this respect. We have compared the biocatalytic and biosorptive removal rates of di-n-butyl phthalate (DBP) and diethyl phthalate (DEP), chosen to represent two environmentally prominent PEs of differing structure and hydrophobicity, by marine-, freshwater-, and terrestrial-derived fungal strains. Bisphenol A, both an extensively used plastic additive and prominent environmental xenoestrogen, was included as a reference compound due to its well-documented fungal degradation. Partial pathways of DBP metabolization by the ecophysiologically diverse asco- and basidiomycete strains tested were proposed with the help of UPLC-QTOF-MS analysis. Species specific biochemical reaction steps contributing to DBP metabolism were also observed. The involved reactions include initial cytochrome P450-dependent monohydroxylations of DBP with subsequent further oxidation of related metabolites, de-esterification via either hydrolytic cleavage or cytochrome P450-dependent oxidative O-dealkylation, transesterification, and demethylation steps - finally yielding phthalic acid as a central intermediate in all pathways. Due to the involvement of ecophysiologically and phylogenetically diverse filamentous and yeast-like fungi native to marine, freshwater, and terrestrial habitats the results of this study outline an environmentally ubiquitous pathway for the biocatalytic breakdown of plastic additives. Beyond previous research into fungal PE metabolism which emphasizes hydrolytic de-esterification as the primary catabolic step, a prominent role of cytochrome P450 monooxygenase-catalyzed reactions is established.
Highlights
Environmental plastic pollution poses a global threat to ecosystems and human health
A comparatively weaker effect of piperonyl butoxide (PB) on di-n-butyl phthalate (DBP) removal could be inferred for Phoma sp. (Figure 2 and Table 2). These results clearly indicate the involvement of cytochrome P450 monooxygenases in the first biocatalytic step of DBP removal in these fungi
ultra performance liquid chromatography (UPLC)-QTOF-MS analysis of DBP metabolites in fungal cultures confirmed DBP biotransformation and enabled us to establish the major biochemical reaction steps contributing to DBP metabolization in the Baltic Sea isolate Ascocoryne sp., the freshwater-derived strain Phoma sp., the environmentally ubiquitous mold S. chlorohalonata
Summary
Environmental plastic pollution poses a global threat to ecosystems and human health. Loss can occur at any stage of product lifestyle, with chemical leaching relevant to plasticizers as the absence of covalent binding to the plastic resin leaves their migration unhindered (Cartwright et al, 2000; Gao and Wen, 2016; Hahladakis et al, 2018). PEs have been recorded in atmospheric samples from remote regions of the Atlantic and Arctic Oceans, and are found in human breast milk, blood, and urine (Net et al, 2015). A study published in the International Journal of Hygiene and Environmental Health detected such compounds in urine samples of a remote Bolivian forager-horticulturist group, suggesting widespread exposure even out with industrialized populations (Sobolewski et al, 2017)
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