Simplified extraction of bisphenols from bacterial culture suspensions and solid matrices

Deconstructed Plastic Substrate Preferences of Microbial Populations from the Natural Environment

Over half of the world's plastic waste is landfilled, where it is estimated to take hundreds of years to degrade. Given the continued use and disposal of plastic products, it is vital that we develop fast and effective ways to utilize plastic waste. Here, we explore the potential of tandem chemical and biological processing to process various plastics quickly and effectively. Four samples of compost or sediment were used to set up enrichment cultures grown on mixtures of compounds, including disodium terephthalate and terephthalic acid (monomers of polyethylene terephthalate), compounds derived from the chemical deconstruction of polycarbonate, and pyrolysis oil derived from high-density polyethylene plastics. Established enrichment communities were also grown on individual substrates to investigate the substrate preferences of different taxa. Biomass harvested from the cultures was characterized using 16S rRNA gene amplicon sequencing and shotgun metagenomic sequencing. These data reveal low-diversity microbial communities structured by differences in culture inoculum, culture substrate source plastic type, and time. Microbial populations from the classes Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, and Acidobacteriae were significantly enriched when grown on substrates derived from high-density polyethylene and polycarbonate. The metagenomic data contain abundant aromatic and aliphatic hydrocarbon degradation genes relevant to the biodegradation of deconstructed plastic substrates used here. We show that microbial populations from diverse environments are capable of growth on substrates derived from the chemical deconstruction or pyrolysis of multiple plastic types and that paired chemical and biological processing of plastics should be further developed for industrial applications to manage plastic waste. IMPORTANCE The durability and impermeable nature of plastics have made them a popular material for numerous applications, but these same qualities make plastics difficult to dispose of, resulting in massive amounts of accumulated plastic waste in landfills and the natural environment. Since plastic use and disposal are projected to increase in the future, novel methods to effectively break down and dispose of current and future plastic waste are desperately needed. We show that the products of chemical deconstruction or pyrolysis of plastic can successfully sustain the growth of low-diversity microbial communities. These communities were enriched from multiple environmental sources and are capable of degrading complex xenobiotic carbon compounds. This study demonstrates that tandem chemical and biological processing can be used to degrade multiple types of plastics over a relatively short period of time and may be a future avenue for the mitigation of rapidly accumulating plastic waste.

Biologically mediated abiotic degradation (BMAD) of bisphenol A by manganese-oxidizing bacteria

Bisphenol A (BPA), a chemical of environmental concern, is recalcitrant under anoxic conditions, but is susceptible to oxidative degradation by manganese(IV)-oxide (MnO₂). Microbial Mn(II)-oxidation generates MnO_2-bio; however, BPA degradation in cultures of Mn(II)-oxidizing bacteria has not been explored. We assessed MnO_2-bio-mediated BPA degradation using three Mn(II)-oxidizing bacteria, Roseobacter sp. AzwK-3b, Erythrobacter sp. SD-21, and Pseudomonas putida GB-1. In cultures of all three strains, enhanced BPA degradation was evident in the presence of Mn(II) compared to replicate incubations without Mn(II), suggesting MnO_2-bio mediated BPA degradation. Increased Mn(II) concentrations up to 100 µM resulted in more MnO_2-bio formation but the highest BPA degradation rates were observed with 10 µM Mn(II). Compared to abiotic BPA degradation with 10 μM synthetic MnO₂, live cultures of strain GB-1 amended with 10 μM Mn(II) consumed 9-fold more BPA at about 5-fold higher rates. Growth of strain AzwK-3b was sensitive to BPA and the organism showed increased tolerance against BPA in the presence of Mn(II), suggesting MnO_2-bio alleviated the inhibition by mediating BPA degradation. The findings demonstrate that Mn(II)-oxidizing bacteria contribute to BPA degradation but organism-specific differences exist, and for biologically-mediated-abiotic-degradation (BMAD), Mn-flux, rather than the absolute amount of MnO_2-bio, is the key determinant for oxidation activity.

Bisphenol A degradation pathway and associated metabolic networks in Escherichia coli harboring the gene encoding CYP450

Although bisphenol A (BPA) can be transformed by CYP450, the metabolic networks involved in regulating the transformation processes are not clear. In this study, Escherichia coli harboring the gene encoding CYP450 was used as a model to elucidate the BPA degradation pathway and the associated metabolic network using a proteomic approach. The results showed that CYP450 promotes the transformation of BPA, generating 1,2-bis(4-hydroxyphenyl)-2-propanol and 2,2-bis(4-hydroxyphenyl)-1-propanol, with hydroquinone and 4-(2-hydroxypropan-2-yl)phenol formed in another pathway. The DNA adducts formed by 1,4-benzoquinone were reduced, and CYP450 played a positive role in cellular homeostasis by promoting the transformation of BPA and mismatch repair. An increase in the synthesis of cell membrane lipids was observed after dislodging BPA. BPA disturbed folate metabolism by decreasing the abundance of dihydrofolate reductase, which inhibited microbial metabolism in the absence of CYP450. The findings of this study revealed the molecular mechanism associated with the metabolic network responsible for pollutant tolerance and degradation.

Chlorothalonil biotransformation by cytochrome P450 monooxygenases in Sclerotinia homoeocarpa

Cytochrome P450s have been shown to play a vital role in the xenobiotic detoxification system of Sclerotinia homoeocarpa, the causal agent of the turfgrass disease dollar spot. A previous study indicated that three CYP450s were validated to play a functional role in resistance against different fungicide classes including propiconazole and plant growth regulator, flurprimidol. In this study, we present these CYP450s possess the capability to modify the multi-site mode of action fungicide chlorothalonil. Chlorothalonil is an extensively used contact fungicide and has been shown to persist in soils. High Performance Liquid Chromatography (HPLC) indicated faster rates of chlorothalonil biotransformation by CYP561 and CYP65 overexpression strains when compared to the wild-type and CYP68 overexpression strain. Our GC-MS results show that the primary transformation intermediate found in soils, 4-hydroxy-2,5,6 trichloro-isophthalonitrile is produced by CYP450s' metabolism. These findings suggest fungal CYP450s can biotransform chlorothalonil for biodegradation or detoxification.

Fate of 14C-bisphenol F isomers in an oxic soil and the effects of earthworm

Bisphenol F (BPF) pollution in environment increased, but the studies on its fate and uptake in soil-earthworm systems were limited. Using ¹⁴C-tracers, environmental fate of BPF isomers in an oxic rice soil with/without earthworm Metaphire guillelmi was studied. After 59 days of incubation, mineralization increased in the order of 2,2'-BPF (18.7% ± 0.3% of the initial amount) < 2,4'-BPF (21.7% ± 0.2%) < 4,4'-BPF (26.9% ± 0.1%). About 70% was converted to bound residues (BRs) and most of the BRs resided in the humin fraction by physical entrapment and ester-linkages. M. guillelmi decreased the mineralization and BRs of 4,4'-BPF in soil, indicating that earthworm increased the ecological risk of 4,4'-BPF. About 5.2% ± 0.1% of the initial amount was accumulated in M. guillelmi and mostly in gut. Considerable amounts of the accumulated 4,4'-BPF were present as earthworm-bound residues (earthworm-BRs). The elimination of 4,4'-BPF from M. guillelmi was very slow, and there was still 96.2% of the initial accumulated radioactivity presented in earthworm after 5 days of depuration. The results of this study firstly provide the isomer - specific partitioning of three BPF isomers in an oxic soil and the uptake and depuration of 4,4'-BPF in earthworm during soil incubation.

A Xenobiotic Detoxification Pathway through Transcriptional Regulation in Filamentous Fungi

Fungi are known to utilize transcriptional regulation of genes that encode efflux transporters to detoxify xenobiotics; however, to date it is unknown how fungi transcriptionally regulate and coordinate different phases of detoxification system (phase I, modification; phase II, conjugation; and phase III, secretion). Here we present evidence of an evolutionary convergence between the fungal and mammalian lineages, whereby xenobiotic detoxification genes (phase I coding for cytochrome P450 monooxygenases [CYP450s] and phase III coding for ATP-binding cassette [ABC] efflux transporters) are transcriptionally regulated by structurally unrelated proteins. Following next-generation RNA sequencing (RNA-seq) analyses of a filamentous fungus, Sclerotinia homoeocarpa, the causal agent of dollar spot on turfgrasses, a multidrug resistant (MDR) field strain was found to overexpress phase I and III genes, coding for CYP450s and ABC transporters for xenobiotic detoxification. Furthermore, there was confirmation of a gain-of-function mutation of the fungus-specific transcription factor S. homoeocarpa XDR1 (ShXDR1), which is responsible for constitutive and induced overexpression of the phase I and III genes, resulting in resistance to multiple classes of fungicidal chemicals. This fungal pathogen detoxifies xenobiotics through coordinated transcriptional control of CYP450s, biotransforming xenobiotics with different substrate specificities and ABC transporters, excreting a broad spectrum of xenobiotics or biotransformed metabolites. A Botrytis cinerea strain harboring the mutated ShXDR1 showed increased expression of phase I (BcCYP65) and III (BcatrD) genes, resulting in resistance to fungicides. This indicates the regulatory system is conserved in filamentous fungi. This molecular genetic mechanism for xenobiotic detoxification in fungi holds potential for facilitating discovery of new antifungal drugs and further studies of convergent and divergent evolution of xenobiotic detoxification in eukaryote lineages.IMPORTANCE Emerging multidrug resistance (MDR) in pathogenic filamentous fungi is a significant threat to human health and agricultural production. Understanding mechanisms of MDR is essential to combating fungal pathogens; however, there is still limited information on MDR mechanisms conferred by xenobiotic detoxification. Here, we report for the first time that overexpression of phase I drug-metabolizing monooxygenases (cytochrome P450s) and phase III ATP-binding cassette efflux transporters is regulated by a gain-of-function mutation in the fungus-specific transcription factor in the MDR strains of the filamentous plant-pathogenic fungus Sclerotinia homoeocarpa This study establishes a novel molecular mechanism of MDR through the xenobiotic detoxification pathway in filamentous fungi, which may facilitate the discovery of new antifungal drugs to control pathogenic fungi.

Fate of Bisphenol A in Terrestrial and Aquatic Environments

Bisphenol A (2,2-bis[4-hydroxyphenyl]propane, BPA), the monomer used to produce polycarbonate plastic and epoxy resins, is weakly estrogenic and therefore of environmental and human health interest. Due to the high production volumes and disposal of products made from BPA, polycarbonate plastic and epoxy resins, BPA has entered terrestrial and aquatic environments. In the presence of oxygen, diverse taxa of bacteria, fungi, algae and even higher plants metabolize BPA, but anaerobic microbial degradation has not been documented. Recent reports demonstrated that abiotic processes mediate BPA transformation and mineralization in the absence of oxygen, indicating that BPA is susceptible to degradation under anoxic conditions. This review summarizes biological and nonbiological processes that lead to BPA transformation and degradation, and identifies research needs to advance predictive understanding of the longevity of BPA and its transformation products in environmental systems.