Lignolytic Fungi Research Articles

Application of solid-state fermentation using mushrooms for the production of animal feed.

The increasing growth of agroindustrial activity resulting in excessive amounts of agriwaste has led to the accumulation of a large quantity of lignocellulosic residues all over the world, in particular in deforestation initiatives for the removal of invasive trees in South Africa. These lignocellulosic residues are rich in energy resources and consist of a mixture of natural polymers based on lignin, cellulose, and hemicellulose. The use of lignolytic fungi such as mushrooms in solid-state fermentation could sufficiently degrade the indigestible lignocellulosic components and add medicinal and nutritional value to otherwise unusable, high-energy waste material, which in turn could yield a new method of producing energy-rich fodder for ruminant animals. The digestive type of animal for which the potential feed is developed must be identified and considered before deciding on the bioconversion method and process, as the outcomes for obtaining potentially high-quality feeds for nonruminant and ruminant animals are different. The current study presents data on the bioconversion of lignocellulosic substrate using solid-state fermentation with edible and medicinal mushrooms, Ganoderma lucidumand Pleurotus ostreatus, and a possible new species, to increase digestibility and nutritional value to be applied as ruminant animal feed. The solid-state fermentation process was optimized and the resulting product was analyzed for the degradation of the lignocellulosic components. Results indicated that the solid-state fermentation duration and mushroom species were key components in achieving significant degradation. Data obtained after 18 weeks of degradation indicated a significant (p < 0.05) reduction in the acid detergent fiber, acid detergent lignin, and neutral detergent fiber fractions of the biomass, with up to a 20% reduction in indigestible components. This increase in digestibility could contribute to increased energy availability for ruminant animals.

Review of lignolytic fungi invading wood, and leather and control of selected fungi by using volatile essential oil of plant origin

Several cultural and historical objects are made up of wood and leather that are prone to the attack of wood- and leather-degrading microorganisms. Lignolytic fungi have a huge potential to degrade such historical objects that are made up of wood and leather. To protect these types of objects from lignolytic fungi, several chemical agents are being used which have a significant impact on the environment that necessitates sustainable approaches to control these microorganisms. In the present study, seven lignolytic fungi (four from wood and three from leather) were isolated and were identified as Colletotrichum capsici, Phoma spp., Aspergillus niger, Fusarium oxysporum, Aspergillus flavus, Aspergillus paraciticus and Colletotrichum capsici-1. All these fungi were able to produce a significant quantity of lignin peroxidase enzyme which confirms that these do have the potential to degrade wood and leather objects. 1200 mg/L was found to be the minimum inhibitory concentration for Aspergillus flavus, Colletotrichum capsici, Fusarium oxysporum, Colletotrichum capsici-1 and Aspergillus parasiticus. However, growth of Aspergillus niger and Phoma spp. was invisible at a concentration of 1400 mg/L, which is the minimum inhibitory concentration of Eucalyptus oil for Aspergillus niger and Phoma spp. At a concentration of 1200 mg/L of Eucalyptus oil, growth of Aspergillus flavus, Colletotrichum capsici-1, Fusarium oxysporum, Colletotrichum capsici and Aspergillus parasiticus was completely inhibited, while 100% growth inhibition was found for Aspergillus niger and Phoma spp. at 1400 mg/L of Eucalyptus oil. This study revealed that these lignolytic fungi may causes degradation of wood and leather made historical objects due to the presence of several organic compounds in Eucalyptus oil that have high anti-fungal activity. It was found that Eucalyptus oil has huge potential to control growth of lignolytic fungi including C. capsici, Phoma spp., A. niger, F. oxysporum, A. flavus, A. paraciticus and C. capsici-1 to protect wood and leather made historical objects in a sustainable and environmentally friendly way.

Diversitas dan Potensi Jamur Lignolitik Asal Seresah Daun

One of the biological agents in the biodegradation of organic waste is fungi. Some fungi have the Lignase enzyme, which can degrade Lignin (one of the main organic waste constituents) into simple sugars. The diversity and potential of organic waste degrading fungi still need much research to obtain potential types of fungi that can be developed in organic waste management. This study aimed to determine the diversity and potential of lignolytic fungi in the biodegradation of organic waste. The research was conducted using a descriptive method to take leaf and soil litter samples, isolate and purify fungi, and test lignolytic potential. Based on the isolation results from leaf litter samples, 16 types of fungal isolates were obtained. The lignolytic potential test was carried out using the Bavendamm method. In screening for potential lignolytic ability using the bavendamm method, 7 isolates were found to be positive. The highest lignolytic activity ratio was SR4BD isolate with a ratio value of 1.9. The results showed that the SR4BD isolate was Fusarium sp.

Exploration of Lignocellulolytic Microbes in Oil Palm Rhizosphere on Peat Soils and Their Respiration Activities

Microbial respiration in peatlands plays a role in contributing CO2 emissions. Studies of microbial exploration and respiration on peat soils in oil palm plantations have not been widely reported. This study aims to explore lignocellulolytic microbes found in peat soils in compared with mineral soils planted with 12-year-old oil palm. Exploration is done by growing the samples on the specific medium of each group of microbial functions. In the next stage, the culture obtained was analysed the respiration activity based on the oxidation of peroxidase catalysis using a chromogen substrate (tetramethylbenzidine) and measured using spectrophotometry at a wavelength of 450 nm. The results showed that both in mineral and peat planted with oil palm in a depths of 0-20 cm were found lignolytic fungi with a population of 17 x 102. Similar results were also found in peat with fern vegetation but at a depth of 20-40 cm. Lignolytic bacteria (methylene blue degradation) can be found on peat soils planted with oil palm at a depth of 0-60 cm and the population increases with increasing depth. This bacterium is also found on peat soils with fern vegetation and mineral soils planted with palm. At a depth of 0-20 cm the population of lignolytic bacteria in non-oil palm peat is highest. Cellulolytic bacteria were isolated at a depth of 0-60 cm. Cellulolytic bacterial populations were highest in oil palm peat at all depths compared to other samples. Respiration analysis of several dominant isolates showed fairly high variation between microbial function groups and within the same function group. The lignolytic microbial group degrading methylene blue showed high respiration activity and &nbsp;varies greatly (0.19-1.85 MER). While the respiration activity of cellulolytic bacteria ranged from 0.45 to 0.62 MER.

The effectiveness of various compositions lignolytic and cellulolytic microbes in composting empty fruit bunch palm oil and sugar cane biomass

In sustainable agriculture, the balance of the use of inorganic fertilizers, organic matter and biofertilizers are highly recommended to increase crop production and at the same time maintaining or even improving the soil health and quality. Farm waste such as palm oil empty bunches and chopped sugar cane biomass are abundant and is a useful material to be returned to the soil to fertilize the plants. Constraints of both the material utilization is a very long process of decomposed because it contains lignin and cellulose and difficult to decomposed by microbes. Organic materials palm oil empty bunches and sugar cane biomass inoculated cellulolytic fungi, cellulolytic bacteria, lignolytic fungi, lignolytic bacteria consortia 1%, 2%, 3%, 4%, and without decomposers. The experiments were conducted in randomized block design (RBD) with four replications. Composting each 1 m3 of organic matter carried out aerobically for one month. Largest decrease in cellulose content of palm oil empty bunches and sugar cane biomass obtain on inoculation cellulolytic and lignolytic microbes that was 4% respectively to 64.92% and 61.12%, while the largest decrease in lignin content on palm oil empty bunches contained of 3% decomposer with cellulolytic and lignolytic microbes. While on sugar cane biomass obtained by 4% decomposers cellulolytic and lignolytic microbes. The addition of containing 2% cellulolytic and lignolytic most effective in decreasing the C/N either palm oil empty bunches or sugar cane biomass.

Molecular recognition of wood polyphenols by phase II detoxification enzymes of the white rot Trametes versicolor

Wood decay fungi have complex detoxification systems that enable them to cope with secondary metabolites produced by plants. Although the number of genes encoding for glutathione transferases is especially expanded in lignolytic fungi, little is known about their target molecules. In this study, by combining biochemical, enzymatic and structural approaches, interactions between polyphenols and six glutathione transferases from the white-rot fungus Trametes versicolor have been demonstrated. Two isoforms, named TvGSTO3S and TvGSTO6S have been deeply studied at the structural level. Each isoform shows two distinct ligand-binding sites, a narrow L-site at the dimer interface and a peculiar deep hydrophobic H-site. In TvGSTO3S, the latter appears optimized for aromatic ligand binding such as hydroxybenzophenones. Affinity crystallography revealed that this H-site retains the flavonoid dihydrowogonin from a partially purified wild-cherry extract. Besides, TvGSTO6S binds two molecules of the flavonoid naringenin in the L-site. These data suggest that TvGSTO isoforms could interact with plant polyphenols released during wood degradation.

Anthropogenic N deposition increases soil C storage by reducing the relative abundance of lignolytic fungi

AbstractAtmospheric nitrogen (N) deposition has increased dramatically since preindustrial times and continues to increase across many regions of the Earth. In temperate forests, this agent of global change has increased soil carbon (C) storage, but the mechanisms underlying this response are not understood. One long‐standing hypothesis proposed to explain the accumulation of soil C proposes that higher inorganic N availability may suppress both the activity and abundance of fungi that decay lignin and other polyphenols in soil. In field studies, elevated rates of N deposition have reduced the activity of enzymes mediating lignin decay, but a decline in the abundance of lignolytic fungi has not been definitively documented to date. Here, we tested the hypothesis that elevated rates of anthropogenic N deposition reduce the abundance of lignolytic fungi. We conducted a field experiment in which we compared fungal communities colonizing low‐lignin, high‐lignin, and wood substrates in a northern hardwood forest that is part of a long‐term N deposition experiment. We reasoned that if lignolytic fungi decline under experimental N deposition, this effect should be most evident among fungi colonizing high‐lignin and wood substrates. Using molecular approaches, we provide evidence that anthropogenic N deposition reduces the relative abundance of lignolytic fungi on both wood and a high‐lignin substrate. Furthermore, experimental N deposition increased total fungal abundance on a low‐lignin substrate, reduced fungal abundance on wood, and had no significant effect on fungal abundance on a high‐lignin substrate. We simultaneously examined these responses in the surrounding soil and forest floor, in which we did not observe significant reductions in the relative abundance of lignolytic fungi or in the size of the fungal community; however, we did detect a change in community composition in the forest floor that appears to be driven by a shift away from lignolytic fungi and towards cellulolytic fungi. Our results provide direct evidence that reductions in the abundance of lignolytic fungi are part of the mechanism by which anthropogenic N deposition increases soil C storage.

Isolation and Screening of Lignolytic Fungi from Various Ecological Niches

Lignin is a major noncarbohydrate polyphenolic structural constituent of cell wall of all the vascular plants and is present in association with cellulose and hemicellulose. It is the second most abundant polymer after cellulose. Lignin is well known for its resistance to microbial degradation because of its high molecular weight and various biologically stable carbon-carbon and ether linkages. Seventy two fungal isolates capable of utilizing lignocellulosic biomass were isolated from different ecological samples. When subjected to primary screening by qualitative plate assay method using methyl orange, azure B, guaiacol and tannic acid as indicators for determining the lignolytic potential, 22 isolates were found positive for at least one of the indicators. Six isolates were found to exhibit all the three extracellular enzyme activities on quantitative estimation of laccase, manganese peroxidase and lignin peroxidase activities. Highest laccase activity was produced by ANF238 (3.42U/ml) while highest manganese peroxidase and lignin peroxidase activities were produced by ANF 212 (0.254U/ml) and ANF238 (0.22U/ml) respectively.

Manganese-enhanced degradation of lignocellulosic waste by Phanerochaete chrysosporium: evidence of enzyme activity and gene transcription.

Lignolytic fungi initiate lignocellulose decay by producing extracellular oxidative enzymes. For better understanding the enzymatic degradation of lignocellulose by white-rot fungi, we investigated the effect of manganese on the organic matter loss, manganese peroxidase (MnP) activity, and manganese peroxidase gene (mnp) transcription levels during solid-state fermentation of rice straw with Phanerochaete chrysosporium. The results showed that the addition of manganese improved MnP activity and made it reach the peak earlier, promoted fungal growth at the early period (0-9days), and enhanced the degradation of lignocellulosic waste. The total organic matter loss had a good correlation with fungal biomass during 30days of cultivation, and manganese amendment promoted the ability of P. chrysosporium to degrade lignocellulose. Quantitative real-time RT-PCR revealed the differential expression of mnp1, mnp2, and mnp3: manganese amendment increased the transcription of mnp1 and mnp2 but not mnp3. The results indicated that manganese stimulated mnp transcription levels and played a post-transcriptional role in MnP production. These findings provide opportunity of development in enzymatic degradation of lignocellulosic waste by P. chrysosporium amended with manganese.

Degradation of fluorene and fluoranthene by the basidiomycete Pleurotus ostreatus

The dependence of the degree of fluorene and fluoranthene degradation by the fungus Pleurotus ostreatus D1 on the culture medium composition has been studied. Polycyclic aromatic hydrocarbons (PAHs) have been transformed in Kirk’s medium (under conditions of laccase production) with the formation of a quinone metabolite and 9-fluorenone upon the use of fluoranthene and fluorene as substrates, respectively. More complete degradation with the formation of an intermediate metabolite, phthalic acid that has undergone subsequent utilization, has occurred in basidiomycete-rich medium (under the production of both laccase and versatile peroxidase). The formation of phthalic acid as a metabolite of fluoranthene degradation by lignolytic fungi has been revealed for the first time. The data allow the supposition that both extracellular laccase and laccase on the mycelium surface can participate in the initial stages of PAH metabolism, while versatile peroxidase is necessary for the oxidation of the formed metabolites. A scheme of fluorene metabolism by Pleurotus ostreatus D1 is suggested.

Whole-cell biosensor of cellobiose and application to wood decay detection

Fungal biodegradation of wood is one of the main threats regarding its use as a material. So far, the detection of this decaying process is empirically assessed by loss of mass, when the fungal attack is advanced and woody structure already damaged. Being able to detect fungal attack on wood in earlier steps is thus of special interest for the wood economy. In this aim, we designed here a new diagnostic tool for wood degradation detection based on the bacterial whole-cell biosensor technology. It was designed in diverting the soil bacteria Streptomyces CebR sensor system devoted to cellobiose detection, a cellulolytic degradation by-product emitted by lignolytic fungi since the onset of wood decaying process. The conserved regulation scheme of the CebR system among Streptomyces allowed constructing a molecular tool easily transferable in different strains or species and enabling the screen for optimal host strains for cellobiose detection. Assays are performed in microplates using one-day culture lysates. Diagnostic is performed within one hour by a spectrophotometric measuring of the cathecol deshydrogenase activity. The selected biosensor was able to detect specifically cellobiose at concentrations similar to those measured in decaying wood and in a spruce leachate attacked by a lignolytic fungus, indicating a high potential of applicability to detect ongoing wood decay process.

Evolutionary divergence of Ure2pA glutathione transferases in wood degrading fungi

The intracellular systems of detoxification are crucial for the survival of wood degrading fungi. Within these systems, glutathione transferases could play a major role since this family of enzymes is specifically extended in lignolytic fungi. In particular the Ure2p class represents one third of the total GST number in Phanerochaete chrysosporium. These proteins have been phylogenetically split into two subclasses called Ure2pA and Ure2pB. Ure2pB can be classified as Nu GSTs because of shared structural and functional features with previously characterized bacterial isoforms. Ure2pA can rather be qualified as Nu-like GSTs since they exhibit a number of differences. Ure2pA possess a classical transferase activity, a more divergent catalytic site and a higher structural flexibility for some of them, compared to Nu GSTs. The characterization of four members of this Ure2pA subclass (PcUre2pA4, PcUre2pA5, PcUre2pA6 and PcUre2pA8) revealed specific functional and structural features, suggesting that these enzymes have rapidly evolved and differentiated, probably to adapt to the complex chemical environment associated with wood decomposition.

Bioremediation of distillery effluent by Pleurotus sajor-caju: evaluation of the influence of pH in vinasse derived from molasses

Background The alcohol industry is an excellent representation of the development process in Brazil, it considers the sugar cane as one of the biggest monocultures. As a result of this high production, there is the vinasse, a residue from the alcohol production after the pulp fermentation and distillation of the wine (Pulp after fermentation), ensuing from 8 to 15 liters for each liter of ethanol produced. This high colored effluent and an objectionable odor is rich in nutrients, mainly in organic matter, having a high potencial poluent when it is inaccordingly in the environment [1,2]. Lignolytic fungi can be used to the remediation of the pollutants, such as vinasse, by the action of peroxidases. So, the search is interested in reducing the contaminations caused by the direct application of the vinasse on the earth without a previous treatment. Therefore the objective is to characterize the biodegradation of the residue through the basidiomycetes Pleurotus sajor-cajuCCB 020 and consequently to produce enzymes with biotechnological potential, decoloring the vinasse and minimizing the polluter potential. After the treatment of the vinasse, it shows several goals as the fertirrigation, the water reuse for the washing proccess of the sugar cane and/or other activities related to the industrial process.

Transcriptomic responses of Phanerochaete chrysosporium to oak acetonic extracts: focus on a new glutathione transferase.

The first steps of wood degradation by fungi lead to the release of toxic compounds known as extractives. To better understand how lignolytic fungi cope with the toxicity of these molecules, a transcriptomic analysis of Phanerochaete chrysosporium genes was performed in the presence of oak acetonic extracts. It reveals that in complement to the extracellular machinery of degradation, intracellular antioxidant and detoxification systems contribute to the lignolytic capabilities of fungi, presumably by preventing cellular damages and maintaining fungal health. Focusing on these systems, a glutathione transferase (P. chrysosporium GTT2.1 [PcGTT2.1]) has been selected for functional characterization. This enzyme, not characterized so far in basidiomycetes, has been classified first as a GTT2 compared to the Saccharomyces cerevisiae isoform. However, a deeper analysis shows that the GTT2.1 isoform has evolved functionally to reduce lipid peroxidation by recognizing high-molecular-weight peroxides as substrates. Moreover, the GTT2.1 gene has been lost in some non-wood-decay fungi. This example suggests that the intracellular detoxification system evolved concomitantly with the extracellular ligninolytic machinery in relation to the capacity of fungi to degrade wood.

Induction and suppression of Dichomitus squalens and Ceriporiopsis subvermispora peroxidase activity by manganese sulphate in response to carbon and nitrogen sources

AbstractDelignification is critical in the production of biofuel from a potentially abundant renewable resource, lignocellulosic waste. One of the classes of lignolytic enzymes are peroxidases. Manganese sulphate (Mn2+) has a significant impact on the peroxidase activity of lignolytic fungi. Along with induction, the suppression of peroxidase activity by Mn2+ has been observed. Peroxidase regulation is governed by three critical Mn2+ concentrations: the minimum inductive concentration (MIC), the peak concentration (PC) and the minimum suppressive concentration (MSC). The induction and suppression of enzyme activity were not associated with fungal growth capacity, but with a specific enzyme response to the nutritional conditions. Manipulation of the carbon and nitrogen sources shifted the peroxidase suppression by Mn2+ to high concentrations and, hence, increased the peroxidase tolerance to Mn2+ and, consequently, peak peroxidase activities. The manipulation of carbon and nitrogen sources allowed increasing the peak concentrations of Mn2+ and corresponding peroxidase activity up to 0.5 mg/mL and 180.70 AU (173% increase compared to standard) in C. subvermispora, and up to 0.05 mg/mL and 151.23 AU in D. squalens (91% increase compared to standard). Thus, manipulation of carbon and nitrogen sources is a useful tool in enhancing fungi peroxidase tolerance to Mn2+ and improving the delignification of lignocellulosic biomass by fungi to prepare an easily consumable substrate for economically viable biofuel production.

Comparative efficiency of different pretreatment methods on enzymatic digestibility of Parthenium sp.

The potential of Parthenium sp. as a feedstock for enzymatic saccharification was investigated by using chemical and biological pretreatment methods. Mainly chemical pretreatments (acid and alkali) were compared with biological pretreatment with lignolytic fungi Marasmiellus palmivorus PK-27. Structural and chemical changes as well as crystallinity of cellulose were examined through scanning electron microscopy, fourier transform infra red and X-ray diffraction analysis, respectively after pretreatment. Total reducing sugar released during enzymatic saccharification of pretreated substrates was also evaluated. Among the pretreatment methods, alkali (1% NaOH) treated substrate showed high recovery of acid perceptible polymerised lignin (7.53 ± 0.5 mg/g) and significantly higher amount of reducing sugar (513.1 ± 41.0 mg/gds) compared to uninoculated Parthenium (163.4 ± 21.2) after 48 h of hydrolysis. This is the first report of lignolytic enzyme production from M. palmivorus, prevalent in oil palm plantations in Malaysia and its application in biological delignification of Parthenium sp. Alkali (1% NaOH) treatment proves to be the suitable method of pretreatment for lignin recovery and enhanced yield of reducing sugar which may be used for bioethanol production from Parthenium sp.

Influence of selected biowaste materials pre-treatment on their anaerobic digestion

AbstractThe topic of this study is the pre-treatment of substrates for anaerobic digestion. Two different substrates of algae Scenedesmus subspicatus (SAG 86.81), Chlorella kessleri (LARG/1) and foliage of Prunus serrulata were subjected to anaerobic digestion. A mixture of commercially available cellulolytic enzymes (Analytical science s.r.o., Modra, Slovakia) was used for anaerobic treatment of algae while the foliage of Prunus serrulata was pre-treated by lignolytic fungi. The highest production of methane per mass of volatile solids was reached with untreated Chlorella kessleri at (0.59 ± 0.04) L g−1. The addition of cellulolytic enzymes did not increase the production of methane from the algal substrate; however, a faster substrate degradation and thus also higher speed of methane production at the beginning of cultivation was achieved. After foliage pre-treatment by fungal isolate Pleurotus pulmonarius, isolated from natural habitats, the methane production increased five times. In this way we were able to speed up the processes of biological degradation of ligno-cellulose materials and thereby to increase the production of methane. Our results show the possibility of using algae as a suitable substrate for biogas production. On the other hand, also aerobic pre-treatment of foliage (Pleurotus pulmonarius) presents a successful way for speeding up the degradation of ligno-cellulose waste leading to increased methane yields.

Bioconversion of Municipal Solid Waste (MSW) and Water Hyacinth (WH) into organic manure by fungal consortium

The present study was carried out to assess the degrading efficiency of the fungal consortium (Cellulolytic fungi - Paecilomyces variotti and Chaetomium globosum, lignolytic fungi – Pleurotus florida and Tramates versicolor and actinomycetes - Streptomyces lavendulae and Thermobifida fusca ) in converting the Municipal solid waste (MSW) and Water hyacinth (WH) mixture into an eco-friendly value added organic manure .The results revealed that the biomanure obtained by inoculation of fungal consortium into the municipal solid waste (MSW) and water hyacinth (WH) mixture was found to be efficient in enhancing the rate of decomposition with in 90 days of biodegradation as they showed drastic reduction in the biochemical parameters like organic carbon (21.09 per cent), cellulose (20.56 per cent), phenolic content(0.46 mg g-1) and reducing sugars (0.67 mg g-1). C:N ratio was narrowed down from 92:1 to 15:1, while nitrogen content increased to 1.39 per cent from 0.37 percent compared to uninoculated control (uninoculated MSW-WH compost). ?-glucosidase and urease enzyme activities were much pronounced upto 75 days from 0.05 to 1.69 Ul -1enzyme protein (?-glucosidase) and from 0.93 to 1.89 µ mol of ammonia formed mg -1enzyme protein (urease) in fungal consortium inoculated MSW-WH over the uninoculated MSW-WH compost.

Biochemistry of microbial polyvinyl alcohol degradation

Effect of minor chemical structures such as 1,2-diol content, ethylene content, tacticity, a degree of polymerization, and a degree of saponification of the main chain on biodegradability of polyvinyl alcohol (PVA) is summarized. Most PVA-degraders are Gram-negative bacteria belonging to the Pseudomonads and Sphingomonads, but Gram-positive bacteria also have PVA-degrading abilities. Several examples show symbiotic degradation of PVA by different mechanisms. Penicillium sp. is the only reported eukaryotic degrader. A vinyl alcohol oligomer-utilizing fungus, Geotrichum fermentans WF9101, has also been reported. Lignolytic fungi have displayed non-specific degradation of PVA. Extensive published studies have established a two-step process for the biodegradation of PVA. Some bacteria excrete extracellular PVA oxidase to yield oxidized PVA, which is partly under spontaneous depolymerization and is further metabolized by the second step enzyme (hydrolase). On the other hand, PVA (whole and depolymerized to some extent) must be taken up into the periplasmic space of some Gram-negative bacteria, where PVA is oxidized by PVA dehydrogenase, coupled to a respiratory chain. The complete pva operon was identified in Sphingopyxis sp. 113P3. Anaerobic biodegradability of PVA has also been suggested.

Engineered Nanomaterial Transformation under Oxidative Environmental Conditions: Development of an in vitro Biomimetic Assay

Once released into the environment, engineered nanomaterials may be transformed by microbially mediated redox processes altering their toxicity and fate. Little information currently exists on engineered nanomaterial transformation under environmentally relevant conditions. Here, we report the development of an in vitro biomimetic assay for investigation of nanomaterial transformation under simulated oxidative environmental conditions. The assay is based on the extracellular hydroquinone-driven Fenton's reaction used by lignolytic fungi. We demonstrate the utility of the assay using CdSe(core)/ZnS(shell) quantum dots (QDs) functionalized with poly(ethylene glycol). QD transformation was assessed by UV-visible spectroscopy, inductively coupled plasma-optical emission spectroscopy, dynamic light scattering, transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). QDs were readily degraded under simulated oxidative environmental conditions: the ZnS shell eroded and cadmium was released from the QD core. TEM, electron diffraction analysis, and EDX of transformed QDs revealed formation of amorphous Se aggregates. The biomimetic hydroquinone-driven Fenton's reaction degraded QDs to a larger extent than did H202 and classical Fenton's reagent (H2O2 + Fe2+). This assay provides a new method to characterize transformations of nanoscale materials expected to occur under oxidative environmental conditions.