Biodegradation Of Organic Contaminants Research Articles

Enhancing in situ biodegradation in groundwater using pump and treat remediation: a proof of concept and modelling analysis of controlling variables.

A remediation approach which uses pump and treatment (PAT) to enhance the biodegradation of organic contaminants by increasing dispersive mixing between plumes and groundwater was evaluated for a phenol-contaminated aquifer, using a reactive transport model which simulates kinetic reactions between an electron donor (ED) in the plume and electron acceptor (EA) in the groundwater. The influence of system design and operation was examined in six modelling scenarios. Injection or extraction of groundwater increases biodegradation above no action and the location, pumping rate, and distance between well(s) are important variables which influence biodegradation. An increase in pumping rate, distance of the wells from the plume centreline, and changing the flow direction increase dispersive mixing between the plume and groundwater. This increases plume spreading and the plume fringe interface, providing a greater flux of dissolved EAs for biodegradation. In general, injection of groundwater containing natural EAs enhances biodegradation more than extraction. The enhancement of biodegradation is sensitive to the relative fluxes of ED and EA, as controlled by the arrangement of the wells. In the best performing scenario, biodegradation was enhanced by 128%, compared with no action.

Characterization of Hsp17, a Novel Small Heat Shock Protein, in Sphingomonas melonis TY under Heat Stress.

Bacteria are constantly exposed to a variety of environmental stresses. Temperature is considered one of the most important environmental factors affecting microbial growth and survival. As ubiquitous environmental microorganisms, Sphingomonas species play essential roles in the biodegradation of organic contaminants, plant protection, and environmental remediation. Understanding the mechanism by which they respond to heat shock will help further improve cell resistance by applying synthetic biological strategies. Here, we assessed the transcriptomic and proteomic responses of Sphingomonas melonis TY to heat shock and found that stressful conditions caused significant changes in functional genes related to protein synthesis at the transcriptional level. The most notable changes observed were increases in the transcription (1,857-fold) and protein expression (11-fold) of Hsp17, which belongs to the small heat shock protein family, and the function of Hsp17 in heat stress was further investigated in this study. We found that the deletion of hsp17 reduced the capacity of the cells to tolerate high temperatures, whereas the overexpression of hsp17 significantly enhanced the ability of the cells to withstand high temperatures. Moreover, the heterologous expression of hsp17 in Escherichia coli DH5α conferred to the bacterium the ability to resist heat stress. Interestingly, its cells were elongated and formed connected cells following the increase in temperature, while hsp17 overexpression restored their normal morphology under high temperature. In general, these results indicate that the novel small heat shock protein Hsp17 greatly contributes to maintaining cell viability and morphology under stress conditions. IMPORTANCE Temperature is generally considered the most important factor affecting metabolic functions and the survival of microbes. As molecular chaperones, small heat shock proteins can prevent damaged protein aggregation during abiotic stress, especially heat stress. Sphingomonas species are widely distributed in nature, and they can frequently be found in various extreme environments. However, the role of small heat shock proteins in Sphingomonas under high-temperature stress has not been elucidated. This study greatly enhances our understanding of a novel identified protein, Hsp17, in S. melonis TY in terms of its ability to resist heat stress and maintain cell morphology under high temperature, leading to a broader understanding of how microbes adapt to environmental extremes. Furthermore, our study will provide potential heat resistance elements for further enhancing cellular resistance as well as the synthetic biological applications of Sphingomonas.

Functional Genes Profile of Atmospheric Dust in the East Mediterranean Suggests Widespread Anthropogenic Influence on Aerobiome Composition

AbstractThe microbiome of atmospheric dust events has raised increasing interest in the last decade, resulting in numerous studies that characterized the different parameters affecting the composition of the atmospheric microbiome, that is, the aerobiome. However, less is known about the functional profile of the aerobiome and how it compares with other environments. Here, we describe the results of shotgun metagenome analysis conducted on a representative set of particulate matter (PM) samples taken in Israel under dusty and nondusty conditions. We compared the functional profiles of these samples to local metagenomes collected from soils, sea, and leaf surfaces and to PM collected in Saudi Arabia, in order to link between the sampled aerosols and potential sources that contribute to the aerobiome. We found that PM samples collected in Israel most resembled Saudi Arabian dust and Israeli soils in both community composition and functional genes profile. In addition, we found significant differences in the abundances of genes associated with anthropogenic activity. Specifically, the examined dust exhibited a significantly higher abundance of genes associated with the biodegradation of organic contaminants, mostly benzoate and aminobenzoate, compared with all other examined environments. These preliminary results suggest that an anthropogenic impact on the aerobiome composition and functional profile is widespread, and pave the path to understanding the role of dust storms in disseminating microorganisms in various environments, spreading various traits, and affecting humans, livestock, plants, and ecosystem health.

Combining flowform cascade with constructed wetland to enhance domestic wastewater treatment

This study reports the performance of a new combined flowform cascade (FC) and constructed wetland (CW) system to enhance nitrogen removal and biological degradation of urban wastewater. A series of 8 FC units at the flow rate of 200 L/h could markedly increase the dissolved oxygen level in the wastewater from the initial value of 0.2 mg/L to 5.6 mg/L, thus providing suitable aerobic condition in the front zone of the CW for nitrification and biodegradation of organic contaminants. The results demonstrate that the combined FC/CW system could achieve the sequence of aerobic and anoxic conditions for nitrification and denitrification, respectively. By using a series of FC units for aeration, the CW system could enhance the removal of total nitrogen from 49.4% to 71.2% and biochemical oxygen demand from 80.9% to 86.1% when the hydraulic loading rate was 31.25 m3/m2⋅day. On the other hand, the FC units exerted negligible effects on the phosphate and total suspended solid removals of the CW system. Thus, the combined FC/CW process exhibited phosphate and total suspended solid removals comparable to those of the CW alone.

Elucidating the Role of O2 Uncoupling in the Oxidative Biodegradation of Organic Contaminants by Rieske Non-heme Iron Dioxygenases.

Oxygenations of aromatic soil and water contaminants with molecular O2 catalyzed by Rieske dioxygenases are frequent initial steps of biodegradation in natural and engineered environments. Many of these non-heme ferrous iron enzymes are known to be involved in contaminant metabolism, but the understanding of enzyme–substrate interactions that lead to successful biodegradation is still elusive. Here, we studied the mechanisms of O2 activation and substrate hydroxylation of two nitroarene dioxygenases to evaluate enzyme- and substrate-specific factors that determine the efficiency of oxygenated product formation. Experiments in enzyme assays of 2-nitrotoluene dioxygenase (2NTDO) and nitrobenzene dioxygenase (NBDO) with methyl-, fluoro-, chloro-, and hydroxy-substituted nitroaromatic substrates reveal that typically 20–100% of the enzyme’s activity involves unproductive paths of O2 activation with generation of reactive oxygen species through so-called O2 uncoupling. The 18O and 13C kinetic isotope effects of O2 activation and nitroaromatic substrate hydroxylation, respectively, suggest that O2 uncoupling occurs after generation of FeIII-(hydro)peroxo species in the catalytic cycle. While 2NTDO hydroxylates ortho-substituted nitroaromatic substrates more efficiently, NBDO favors meta-substituted, presumably due to distinct active site residues of the two enzymes. Our data implies, however, that the O2 uncoupling and hydroxylation activity cannot be assessed from simple structure–reactivity relationships. By quantifying O2 uncoupling by Rieske dioxygenases, our work provides a mechanistic link between contaminant biodegradation, the generation of reactive oxygen species, and possible adaptation strategies of microorganisms to the exposure of new contaminants.

Predicted functional genes for the biodegradation of xenobiotics in groundwater and sediment at two contaminated naval sites.

The goals of this study were to predict the genes associated with the biodegradation of organic contaminants and to examine microbial community structure in samples from two contaminated sites. The approach involved a predictive bioinformatics tool (PICRUSt2) targeting genes from twelve KEGG xenobiotic biodegradation pathways (benzoate, chloroalkane and chloroalkene, chlorocyclohexane and chlorobenzene, toluene, xylene, nitrotoluene, ethylbenzene, styrene, dioxin, naphthalene, polycyclic aromatic hydrocarbons, and metabolism of xenobiotics by cytochrome P450). Further, the predicted phylotypes associated with functional genes early in each pathway were determined. Phylogenetic analysis indicated a greater diversity in the sediment compared to the groundwater samples. The most abundant genera for sediments/microcosms included Pseudomonas, Methylotenera, Rhodococcus, Stenotrophomonas, and Brevundimonas, and the most abundant for the groundwater/microcosms included Pseudomonas, Cupriavidus, Azospira, Rhodococcus, and unclassified Burkholderiaceae. Genes from all twelve of the KEGG pathways were predicted to occur. Seven pathways contained less than twenty-five genes. The predicted genes were lowest for xenobiotics metabolism by cytochrome P450 and ethylbenzene biodegradation and highest for benzoate biodegradation. Notable trends include the occurrence of the first genes for trinitrotoluene and 2,4-dinitrotoluene degradation. Also, the complete path from toluene to benzoyl-CoA was predicted. Twenty-two of the dioxin pathway genes were predicted, including genes within the first steps. The following phylotypes were associated with the greatest number of pathways: unclassified Burkholderiaceae, Burkholderia-Caballeronia-Paraburkholderia, Pseudomonas, Rhodococcus, unclassified Betaproteobacteria, and Polaromonas. This work illustrates the value of PICRUSt2 for predicting biodegradation potential and suggests that a subset of phylotypes could be important for the breakdown of organic contaminants or their metabolites. KEY POINTS: • The approach is a low-cost alternative to shotgun sequencing. • The genes and phylotypes encoding for xenobiotic degradation were predicted. • A subset of phylotypes were associated with many pathways.

The effects of heavy metal exposure in agriculture soil on chlorophyll content of agriculture crops: A meta-analysis approach

Soil can be contaminated by the accumulation of heavy metals and metalloids through emissions from rapidly developing industrial areas. Due to the possibility of chemical change (speciation) and their bioavailability, the presence of toxic metals in the soil can greatly inhibit the biodegradation of organic contaminants. The researchers aimed to analyse the effect of heavy metal levels in agricultural soil on chlorophyll levels in agricultural crops through a meta-analysis method which is expected to provide results in the form of a summary of data that already exists in journals that have been published so far. Here we present a meta-analysis of 6 studies (56 data collected) published between 1997 and 2020 that reported the effects of heavy metal content on plant chlorophyll content. Based on the meta-analysis of the effect of heavy metal exposure in agricultural soil on the chlorophyll content of agricultural crops, the value “effect size overall” was -0.285 in the range of -0.380 to -0.190, where most of the values “effect size” were on the left. Plants growing on soil contaminated with heavy metals result in decreased growth due to changes in physiological and biochemical activities, especially when heavy metals inhibit plant growth and development. Furthermore, environmental risk assessment due to mercury exposure is very important to control the transport and accumulation of mercury in the biosphere to reduce the impact of mercury on the environment.

Enhancing the treatment of petrochemical wastewater using redox mediator suspended biofilm carriers

The treatment efficiency of petrochemical wastewater via the traditional activated sludge process is generally unsatisfactory due to the complex and toxic features of petroleum compounds. Redox mediator (RM) can improve the biodegradation of organic contaminants by participating in the microbial extracellular electron transfer process. However, the continuous dosing of the soluble redox mediator would lead to secondary pollution and rise operation cost. In this study, an insoluble and economical redox mediator material (biochar) was introduced into high-density polyethylene (HDPE) to prepare suspended biofilm carriers (RM-modified carriers), and applied in anaerobic/oxic (A/O) reactors. The reactor filled with RM-modified carriers (R3) showed the removal efficiency of chemical oxygen demand (COD) and phenol in the anaerobic zone were 34.6 % and 43.0 % respectively at organic loading rates (OLRs) of 22.2 kg COD/(m3·d), which increased by 6.8 % and 8.3 % respectively compared with that of the reactor filled with conventional HDPE carriers (R2), and increased by 12.4 % and 17.7 % respectively compared with that of the reactor without filled with carriers (R1). Microbial analysis proved that the relative abundance of Bacteroides that participated in electron transfer of R3 improved by approximately 6.3 % compared with that of R2. These findings demonstrated that RM-modified carriers improved the abundance of relevant functional bacteria and enhanced the degradation efficiency of the contaminants in petrochemical wastewater.

Bioaccessibility of 14C-phenanthrene from root amended contaminated soil

Plants and their roots, in particular, may be important in stimulating microbial degradation of organic contaminants in soil. It is also known that bioaccessibility is important in controlling the biodegradation of organic contaminants in soil. This study aimed to assess the impact of plant roots on the biodegradation and bioaccessibility of 14C-phenanthrene in soil in the presence of plant root biomass. To do this, changes in the 14C-phenanthrene mineralisable and hydroxypropyl-β-cyclodextrin (HPCD) extractable fractions were evaluated. After 1, 25, 50 and 100 days of PAH-soil contact time, 12/14C-phenanthrene-spiked soil was amended with roots from two grasses and one legume. Mineralisation and HPCD extractability of 14C-phenanthrene were measured after 1, 21 and 42 days PAH-root-soil contact time. Findings revealed that mineralisation of 14C-phenanthrene was enhanced following the amendment with plant root biomass regardless their species or form, especially in the soils that been aged for ≥50 days soil-PAH contact time. Overall, this study showed that greater levels of phenanthrene biodegradation may be achieved by incorporating root biomass into the contaminated soil, particularly where indigenous catabolic activity has developed. The findings reported here contribute to the understanding of how plant root biomass may impact on contaminant bioaccessibility and stimulate the more effective indigenous biodegradation of hydrocarbons in soil.

The Interactive Effects of Crude Oil and Corexit 9500 on Their Biodegradation in Arctic Seawater.

The risk of petroleum spills coupled with the potential application of chemical dispersants as a spill response strategy necessitates further understanding of the fate of oil and dispersants and their interactive effects during biodegradation. Using Arctic seawater mesocosms amended with either crude oil, Corexit 9500, or both together, we quantified the chemical losses of crude oil and Corexit 9500 and identified microbial taxa implicated in their biodegradation based on shifts in the microbial community structure over a 30-day time course. Chemical analyses included total petroleum hydrocarbons (TPH), n-alkanes, branched alkanes, and polycyclic aromatic hydrocarbons (PAHs) for oil loss and the surfactant components dioctyl sodium sulfosuccinate (DOSS), Span 80, Tween 80, Tween 85, and the DOSS metabolite ethylhexyl sulfosuccinate (EHSS) for Corexit loss. Changes to the microbial communities and identification of key taxa were determined by 16S rRNA gene amplicon sequencing. The nonionic surfactants of Corexit 9500 (Span 80 and Tweens 80 and 85) biodegraded rapidly, dropping to below the limits of detection within 5 days and prior to any detectable initiation of oil biodegradation. This resulted in no observable suppression of petroleum biodegradation in the presence of Corexit compared to that of oil alone. In contrast, biodegradation of DOSS was delayed in the presence of oil, based on the prolonged presence of DOSS and accumulation of the degradation intermediate EHSS that did not occur in the absence of oil. Microbial analyses revealed that oil and Corexit enriched different overall microbial communities, with the presence of both resulting in a community composition that shifted from one more similar to that of Corexit only to one reflecting the oil-only community over time, in parallel with the degradation of predominantly Corexit and then oil components. Some microbial taxa (Oleispira, Pseudofulvibacter, and Roseobacter) responded to either oil or Corexit, suggesting that some organisms may be capable of utilizing both substrates. Together, these findings reveal interactive effects of crude oil and Corexit 9500 on chemical losses and microbial communities as they biodegrade, providing further insight into their fate when copresent in the environment.IMPORTANCE Chemical dispersants such as Corexit 9500 are commonly used in oil spill response and are currently under consideration for use in the Arctic, where their fate and effects have not been well studied. This research was performed to determine the interactive effects of the copresence of crude oil and Corexit 9500 on the degradation of components from each mixture and the associated microbial community structure over time in Arctic seawater. These findings will help yield a better understanding of the biodegradability of dispersant components applied to an oil spill, the temporal microbial community response to dispersed oil, and the fundamental microbial ecology of organic contaminant biodegradation processes in the Arctic marine environment.

The impact of enhanced and non-enhanced biochars on the catabolism of 14C-phenanthrene in soil

Abstract Biochar is a by-product from the pyrolysis of biomass and has a great potential in soil amendment due to its carbon and nutrient-rich properties. The aim of this study was to investigate the impact of increasing amounts (0, 0.01, 0.1, 0.2, 0.5 and 1.0%) of two types of biochar (so-called enhanced and non-enhanced) to soil on the biodegradation of 14C-phenanthrene. Enhanced biochar contains inoculants which are designed to potentially stimulate microbial activity and promote biological function in soil. After 100 d of incubation, the addition of 0.5% and 1% enhanced (EbioC) and non-enhanced biochars (NEbioC) led to longer lag phases, reduced rates and extents of 14C-phenanthrene in amended soil. However, in soils amended with 0.01%, 0.1% and 0.2% amendments, extents of mineralisation of 14C-phenanthrene increased and were found to be higher in the EBioC — as compared to the NEbioC-amended soils. Increasing soil-phenanthrene contact time also increased 14C-phenanthrene mineralisation in soil which had received smaller amounts of EBioC. Application of both EbioC and NEbioC also enriched the soil microbial populations during the incubation. However, it was found that phenanthrene-degrading microbial populations declined as soil contact time increased; this was particularly true for soils receiving larger amounts due to reduction in the mobile/bioaccessible fraction of the phenanthrene in soil. The findings revealed the importance of the type and amount of biochar that may be added to soil to stimulate or enhance organic contaminant biodegradation.

Organic Contaminant Biodegradation by Oxidoreductase Enzymes in Wastewater Treatment.

Organic contaminants (OCs), such as pharmaceuticals, personal care products, flame retardants, and plasticisers, are societally ubiquitous, environmentally hazardous, and structurally diverse chemical compounds whose recalcitrance to conventional wastewater treatment necessitates the development of more effective remedial alternatives. The engineered application of ligninolytic oxidoreductase fungal enzymes, principally white-rot laccase, lignin peroxidase, and manganese peroxidase, has been identified as a particularly promising approach for OC remediation due to their strong oxidative power, broad substrate specificity, low energy consumption, environmental benignity, and cultivability from lignocellulosic waste. By applying an understanding of the mechanisms by which substrate properties influence enzyme activity, a set of semi-quantitative physicochemical criteria (redox potential, hydrophobicity, steric bulk and pKa) was formulated, against which the oxidoreductase degradation susceptibility of twenty-five representative OCs was assessed. Ionisable, compact, and electron donating group (EDG) rich pharmaceuticals and antibiotics were judged the most susceptible, whilst hydrophilic, bulky, and electron withdrawing group (EWG) rich polyhalogenated compounds were judged the least susceptible. OC susceptibility scores were in general agreement with the removal rates reported for experimental oxidoreductase treatments (R2 = 0.60). Based on this fundamental knowledge, and recent developments in enzyme immobilisation techniques, microbiological enzymic treatment strategies are proposed to formulate a new generation of biological wastewater treatment processes for the biodegradation of environmentally challenging OC compounds.

Mass Transfer Limitation during Slow Anaerobic Biodegradation of 2-Methylnaphthalene.

While they are theoretically conceptualized to restrict biodegradation of organic contaminants, bioavailability limitations are challenging to observe directly. Here we explore the onset of mass transfer limitations during slow biodegradation of the polycyclic aromatic hydrocarbon 2-methylnaphthalene (2-MN) by the anaerobic, sulfate-reducing strain NaphS2. Carbon and hydrogen compound specific isotope fractionation was pronounced at high aqueous 2-MN concentrations (60 μM) (εcarbon = -2.1 ± 0.1‰/εhydrogen = -40 ± 7‰) in the absence of an oil phase but became significantly smaller (εcarbon = -0.9 ± 0.3‰/εhydrogen = -6 ± 3‰) or nondetectable when low aqueous concentrations (4 μM versus 0.5 μM) were in equilibrium with 80 or 10 mM 2-MN in hexadecane, respectively. This masking of isotope fractionation directly evidenced mass transfer limitations at (sub)micromolar substrate concentrations. Remarkably, oil-water mass transfer coefficients were 60-90 times greater in biotic experiments than in the absence of bacteria (korg-aq2-MN = 0.01 ± 0.003 cm h-1). The ability of isotope fractionation to identify mass transfer limitations may help study how microorganisms adapt and navigate at the brink of bioavailability at low concentrations. For field surveys our results imply that, at trace concentrations, the absence of isotope fractionation does not necessarily indicate the absence of biodegradation.

Sorption and biodegradation of pharmaceuticals in aerobic activated sludge system: A combined experimental and theoretical mechanistic study

Understanding removal mechanisms of emerging organic contaminants in conventional activated sludge systems is of fundamental and engineering importance. In this study, we selected six environmentally relevant pharmaceuticals as target organic contaminants, namely, metronidazole (MTZ), bezafibrate (BZF), ibuprofen (IBP), sulfamethoxazole (SMX), carbamazepine (CBZ), and ciprofloxacin (CIP) for the mechanistic investigation for their removal. We demonstrated that sorption and biodegradation were the dominant pathways for contaminant removal, while volatilization and hydrolysis were negligible. The sorption removal process varied for the selected pharmaceuticals in the batch system. Then, first-order rate model was used to fit the biodegradation kinetics, and their first-order rate constants (kbio) were ranged from 3.67 × 10−3 to 10.2 L g−1 d−1, in order of CBZ < CIP < SMX < MTZ < BZF < IBP. In order to elucidate the biodegradation mechanism, we calculated a total of twelve geometrical, electrostatic, and quantum chemical descriptors with density functional theory (DFT) approach. Then, correlation analysis was conducted to investigate kbio with these theoretical descriptors. Our results indicate that electrophilicity index (ω), a measure of electrophilic power, influences the biodegradation kinetics to the greatest extent. The ω corresponds to the process where the pharmaceutical molecule acts as an electrophile, adding electron density from a nucleophile. The combined experimental and theoretical results provide insight into the intrinsic nature of biodegradation of organic contaminants of emerging concern during conventional activated sludge treatment.

A new biostimulation approach based on the concept of remaining P for soil bioremediation

C:N:P ratio is generally adopted to estimate the amount of nitrogen and phosphorus to be added to soils to accelerate biodegradation of organic contaminants. However, differences in P fixation among soils lead to varying amounts of available P when a specific dose of the element is applied to different soils. Thus, the application of fertilizers to achieve a previously established C:P ratio leads to biodegradation rates that can be lower than the theoretical maximum. In this study, we developed an equation to estimate the dose of P required to maximize organic contaminant biodegradation in soils as a function of remaining P (P-rem), using diesel as a model contaminant. The soils were contaminated with diesel and received six doses of P. CO2 emission was used to estimate biodegradation of hydrocarbons. Biodegradation increased with P doses. The P level that provided the highest hydrocarbon biodegradation rate showed linear and negative correlation with P-rem. The result shows that the requirement for P decreases as the P-rem of the soil increases (or the P-fixing capacity decreases). The dose of P recommended to maximize hydrocarbon biodegradation rate in soil can be estimated by the formula P (mg/dm3) = 436.5–5.39 × P-rem (mg/L).

Influence of compost and biochar on microbial communities and the sorption/degradation of PAHs and NSO-substituted PAHs in contaminated soils

Diffusely contaminated soils often remain untreated as classical remediation approaches would be disproportionately expensive. Adding compost can accelerate the biodegradation of organic contaminants and adding biochar can immobilize contaminants through sorption. The combined use of compost and biochar to reduce polycyclic aromatic hydrocarbon (PAH) and NSO-substituted PAH contamination has, however, not previously been systematically investigated. We have therefore investigated the processes involved (i) through sorption batch experiments, (ii) by monitoring changes in bacterial, fungal and archaeal communities using denaturing gradient gel electrophoresis, and (iii) through degradation experiments with fluorene, phenanthrene, pyrene, carbazole, dibenzothiophene, and dibenzofuran. Sorption coefficients for organic contaminants in soils increased tenfold following 10% compost addition and up to a hundredfold with further addition of 5% biochar. The rate of PAH and NSO-PAH degradation increased up to twofold following compost addition despite increased sorption, probably due to the introduction of additional microbial species into the autochthonous soil communities. In contrast, degradation of PAHs and NSO-PAHs in soil-compost-biochar mixtures slowed down up to tenfold due to the additional sorption, although some degradation still occurred. The combined use of biochar and compost may therefore provide a strategy for immobilizing PAHs and NSO-PAHs and facilitating degradation of remaining accessible contaminant fractions.

Efficient phytoremediation of organic contaminants in soils using plant-endophyte partnerships.

Soil pollution with organic contaminants is one of the most intractable environmental problems today, posing serious threats to humans and the environment. Innovative strategies for remediating organic-contaminated soils are critically needed. Phytoremediation, based on the synergistic actions of plants and their associated microorganisms, has been recognized as a powerful in situ approach to soil remediation. Suitable combinations of plants and their associated endophytes can improve plant growth and enhance the biodegradation of organic contaminants in the rhizosphere and/or endosphere, dramatically expediting the removal of organic pollutants from soils. However, for phytoremediation to become a more widely accepted and predictable alternative, a thorough understanding of plant-endophyte interactions is needed. Many studies have recently been conducted on the mechanisms of endophyte-assisted phytoremediation of organic contaminants in soils. In this review, we highlight the superiority of organic pollutant-degrading endophytes for practical applications in phytoremediation, summarize alternative strategies for improving phytoremediation, discuss the fundamental mechanisms of endophyte-assisted phytoremediation, and present updated information regarding the advances, challenges, and new directions in the field of endophyte-assisted phytoremediation technology.

Modelling functional resilience of microbial ecosystems: Analysis of governing processes

Functional stability of microbial ecosystems subjected to disturbances is essential for maintaining microbial ecosystem services such as the biodegradation of organic contaminants in terrestrial environments. Functional responses to disturbances are thus an important aspect which is, however, not well understood yet. Here, we present a microbial simulation model to investigate key processes for the recovery of biodegradation. We simulated single disturbances with different spatiotemporal characteristics and monitored subsequent recovery of the biodegradation dynamics. After less intense disturbance events local regrowth governs biodegradation recovery. After highly intense disturbance events the disturbance pattern's spatial configuration is decisive and processes governing local functional recovery vary depending on habitat location with respect to the spatial disturbance pattern. Local regrowth may be unimportant when bacterial dispersal from undisturbed habitats is high. Hence, our results suggest that spatial dynamics are crucial for the robust delivery of the ecosystem service biodegradation under disturbances in terrestrial environments.

Bacterial mineralization of phenanthrene on thermally activated palygorskite: A 14C radiotracer study.

Clay-bacterial interaction can significantly influence the biodegradation of organic contaminants in the environment. A moderate heat treatment of palygorskite could alter the physicochemical properties of the clay mineral and thus support the growth and function of polycyclic aromatic hydrocarbon (PAH)-degrading bacteria. By using 14C-labelled phenanthrene and a model bacterium Burkholderia sartisoli, we studied the mineralization of phenanthrene on the surface of a moderately heat-treated (up to 400°C) palygorskite. The heat treatment at 400°C induced a reduction of binding sites (e.g., by the elimination of organic matter and/or channel shrinkage) in the palygorskite and thus imparted a weaker sequestration of phenanthrene on its surface and within the pores. As a result, a supplement with the thermally modified palygorskite (400°C) significantly increased (20-30%; p<0.05) the biomineralization of total phenanthrene in a simulated soil slurry system. These results are highly promising to develop a clay mineral based technology for the bioremediation of PAH contaminants in water and soil environments.

Carcinogenic risk evaluation for human health risk assessment from soils contaminated with heavy metals

Human activities have progressively increased in recent years. Consequently, significant environment deterioration resulted. Soils have a particularly varied vulnerability to heavy metal pollution, especially in the vicinity of industrial areas. Heavy metal contamination of soil may induce risks and hazards to humans and the ecosystem, while toxic metals in soil can severely inhibit the biodegradation of organic contaminants. This paper is focused on human health risk assessment from extremely contaminated soil with heavy metals, mainly with carcinogenic elements. The study refers to an agricultural area in the vicinity of an old metallurgical processing industrial facility. The contaminants evaluated in the present paper are beryllium (Be), cadmium (Cd), chromium (Cr), nickel (Ni) and lead (Pb). Contamination level is pointed out through laboratory analysis results of soil samples taken from 0–0.2 m, 0.2–0.4 m soil layers and up to 2.1 m soil depth. Some heavy metal concentrations (Cd, Cr and Pb) exceed the intervention thresholds for sensitive areas, as they are stipulated in the national regulation in Romania. The identified average concentration levels of Cd, CrVI and Pb in the first layer of the investigated land are 23.83, 7.71 and 704.22 mg/kgd.w, respectively. The results show that the potential risk of human health is relevant (higher than the acceptable one after World Health Organization) and a possible solution for the remediation should become a major concern for the investigated area.