Enhancing phytoremediation through the use of transgenics and endophytes

Up-regulation of growth-related gene expression in tobacco by volatile compounds released by Bacillus velezensis WSW007

In order to investigate the mechanism of plant growth promoting (PGP) effects of strain Bacillus velezensis WSW007, its PGP traits and production of volatile organic compounds (VOCs) were tested. The effects of VOCs produced by strain WSW007 on plant growth were observed by co-culturing this strain with tobacco seedlings in I-plates. Meanwhile, the effects of VOCs on tobacco gene expression were analysed by a transcriptome analysis and VOCs were identified by solid phase micro extraction coupled with gas chromatography-mass spectrometry (SPME-GC-MS) analysis. As results, strains WSW007 produced acetic acid and siderophore, and could solubilize phosphate; while it also significantly increased the fresh weight of tobacco seedlings via production of VOCs. In transcriptome analysis, plants co-cultured with strain WSW007 presented the highest up-regulated expression for the genes involved in plant growth and development processes, implying that the bacterial VOCs played a role as regulator of plant gene expression. Conclusively, the up-regulation in expression of growth- and development-related genes via VOCs production is an important PGP mechanism in strain B. velezensis WSW007.

Phytoremediation: a transgenic perspective in omics era

Phytoremediation is an environmental safety strategy that might serve as a viable preventative approach to reduce soil contamination in a cost-effective manner. Using plants to remediate pollution from the environment is referred to as phytoremediation. In the past few decades, plants have undergone genetic manipulation to overcome inherent limitations by using genetically modified plants. This review illustrates the eco-friendly process of cleaning the environment using transgenic strategies combined with omics technologies. Herbicides tolerance and phytoremediation abilities have been established in genetically modified plants. Transgenic plants have eliminated the pesticides atrazine and metolachlor from the soil. To expand the application of genetically engineered plants for phytoremediation process, it is essential to test strategies in the field and have contingency planning. Omics techniques were used for understanding various genetic, hormonal, and metabolic pathways responsible for phytoremediation in soil. Transcriptomics and metabolomics provide useful information as resources to understand the mechanisms behind phytoremediation. This review aims to highlight the integration of transgenic strategies and omics technologies to enhance phytoremediation efficiency, emphasizing the need for field testing and comprehensive planning for successful implementation.

SbYS1 and SbWRKY72 regulate Cd tolerance and accumulation in sweet sorghum

MAIN CONCLUSION

SbYS1 and its upstream transcription factor SbWRKY72 were involved in Cd tolerance and accumulation and are valuable for developing sweet sorghum germplasm with high-Cd tolerance or accumulation ability through genetic manipulation. Cadmium (Cd) is highly toxic and can severely affect human health. Sweet sorghum, as an energy crop, shows great potential in extracting cadmium from Cd-contaminated soils. However, its molecular mechanisms of Cd-tolerance and -accumulation remain largely unknown. Here, we isolated a YSL family gene SbYS1 from the sweet sorghum genotype with high Cd accumulation ability and the expression of SbYS1 in roots was induced by cadmium. GUS staining experiment exhibited that SbYS1 was expressed in the epidermis and parenchyma tissues of roots. Further subcellular localization analysis suggested that SbYS1 was localized in the endoplasmic reticulum and plasma membrane. Yeast transformed with SbYS1 exhibited a sensitive phenotype compared to the control when exposed to Cd-NA (chelates of cadmium and nicotianamine), indicating that SbYS1 may absorb cadmium in the form of Cd-NA. Arabidopsis overexpressing SbYS1 had a longer root length and accumulated less Cd in roots and shoots. SbWRKY72 bound to the promoter of SbYS1 and negatively regulated the expression of SbYS1. Transgenic Arabidopsis of SbWRKY72 showed higher sensitivity to cadmium and increased cadmium accumulation in roots. Our results provide references for improving the phytoremediation efficiency of sweet sorghum by genetic manipulation in the future.

Culturable Bacterial Endophytes of Wild White Poplar (Populus alba L.) Roots: A First Insight into Their Plant Growth-Stimulating and Bioaugmentation Potential

The white poplar (Populus alba L.) has good potential for a green economy and phytoremediation. Bioaugmentation using endophytic bacteria can be considered as a safe strategy to increase poplar productivity and its resistance to toxic urban conditions. The aim of our work was to find the most promising strains of bacterial endophytes to enhance the growth of white poplar in unfavorable environmental conditions. To this end, for the first time, we performed whole-genome sequencing of 14 bacterial strains isolated from the tissues of the roots of white poplar in different geographical locations. We then performed a bioinformatics search to identify genes that may be useful for poplar growth and resistance to environmental pollutants and pathogens. Almost all endophytic bacteria obtained from white poplar roots are new strains of known species belonging to the genera Bacillus, Corynebacterium, Kocuria, Micrococcus, Peribacillus, Pseudomonas, and Staphylococcus. The genomes of the strains contain genes involved in the enhanced metabolism of nitrogen, phosphorus, and metals, the synthesis of valuable secondary metabolites, and the detoxification of heavy metals and organic pollutants. All the strains are able to grow on media without nitrogen sources, which indicates their ability to fix atmospheric nitrogen. It is concluded that the strains belonging to the genus Pseudomonas and bacteria of the species Kocuria rosea have the best poplar growth-stimulating and bioaugmentation potential, and the roots of white poplar are a valuable source for isolation of endophytic bacteria for possible application in ecobiotechnology.

Interactions with microbial consortia have variable effects in organic carbon and production of exometabolites among genotypes of Populus trichocarpa

Poplar is a short-rotation woody crop frequently studied for its significance as a sustainable bioenergy source. The successful establishment of a poplar plantation partially depends on its rhizosphere-a dynamic zone governed by complex interactions between plant roots and a plethora of commensal, mutualistic, symbiotic, or pathogenic microbes that shape plant fitness. In an exploratory endeavor, we investigated the effects of a consortium consisting of ectomycorrhizal fungi and a beneficial Pseudomonas sp. strain GM41 on plant growth (including height, stem girth, leaf, and root growth) and as well as growth rate over time, across four Populus trichocarpa genotypes. Additionally, we compared the level of total organic carbon and plant exometabolite profiles across different poplar genotypes in the presence of the microbial consortium. These data revealed no significant difference in plant growth parameters between the treatments and the control across four different poplar genotypes at 7 weeks post-inoculation. However, total organic carbon and exometabolite profiles were significantly different between the genotypes and the treatments. These findings suggest that this microbial consortium has the potential to trigger early signaling responses in poplar, influencing its metabolism in ways crucial for later developmental processes and stress tolerance.

Endophytic Bacillus sp. R1 and Its Roles in Assisting Phytoremediation and Alleviating the Toxicity of Aluminum Combined Phenanthrene Contaminations in Brassica napus

The release of organic and inorganic contaminants into soil from industry, agriculture, and urbanization has become a major issue of international concern, particularly the heavy metals such as aluminum (Al) and the chemical phenanthrene (PHE). Due to their potential toxicity and non-biodegrade in the environment, efficient remediation methods are urgently needed. Recently, research has comprehensively discussed using plants and their endophytes in bioremediation efforts. Endophytic Bacillus sp. R1, isolated from Brassica napus permanently contaminated with Al and PHE, has growth-promoting properties and can efficiently detoxify these contaminants. The pot experiment indicated that compared to the Al combined PHE contaminated soil alone treatment, the R1 treatment led to increased Al accumulation in canola roots across different levels of PHE, Al, and combined PHE and Al contamination. However, Al accumulation in canola shoots and seeds remained unchanged for all treatments. Moreover, PHE in canola roots and shoots was decreased by R1 inoculation and thereby reducing 26.12-60.61% PHE translocated into canola seeds. Additionally, R1 inoculation significantly increased the proportion of extractable Al and, decreased the proportion of acid-soluble inorganic Al and humic-acid Al, but did not affect the concentration of organically complexed Al. In summary, endophyte R1 can degrade PHE, improve canola roots' Al uptake by increasing soil available Al, and scavenge the reactive oxygen species through production of antioxidant enzymes to help alleviate the toxicity of canola co-contaminated with aluminum and phenanthrene.

Exploring the role of microbes for the management of persistent organic pollutants

Persistent organic pollutants (POPs) are chemicals which have been persisting in the environment for many years due to their longer half-lives. POPs have gained attention over the last few decades due to the unsustainable management of chemicals which led to their widespread and massive contamination of biota from different strata and environments. Due to the widespread distribution, bio-accumulation and toxic behavior, POPs have become a risk for organisms and environment. Therefore, a focus is required to eliminate these chemicals from the environment or transform into non-toxic forms. Among the available techniques for the removal of POPs, most of them are inefficient or incur high operational costs. As an alternative to this, microbial bioremediation of POPs such as pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pharmaceuticals and personal care products is much more efficient and cost-effective. Additionally, bacteria play a vital role in the biotransformation and solubilization of POPs, which reduces their toxicity. This review specifies the Stockholm Convention that evaluates the risk profile for the management of existing as well as emerging POPs. The sources, types and persistence of POPs along with the comparison of conventional elimination and bioremediation methods of POPs are discussed comprehensively. This study demonstrates the existing bioremediation techniques of POPs and summaries the potential of microbes which serve as enhanced, cost-effective, and eco-friendly approach for POPs elimination.

Oil-Contaminated Soil Remediation with Biodegradation by Autochthonous Microorganisms and Phytoremediation by Maize (Zea mays)

Biological methods are currently the most commonly used methods for removing hazardous substances from land. This research work focuses on the remediation of oil-contaminated land. The biodegradation of aliphatic hydrocarbons and PAHs as a result of inoculation with biopreparations B1 and B2 was investigated. Biopreparation B1 was developed on the basis of autochthonous bacteria, consisting of strains Dietzia sp. IN118, Gordonia sp. IN101, Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN119, Rhodococcus globerulus IN113 and Raoultella sp. IN109, whereas biopreparation B2 was enriched with fungi, such as Aspergillus sydowii, Aspergillus versicolor, Candida sp., Cladosporium halotolerans, Penicillium chrysogenum. As a result of biodegradation tests conducted under ex situ conditions for soil inoculated with biopreparation B1, the concentrations of TPH and PAH were reduced by 31.85% and 27.41%, respectively. Soil inoculation with biopreparation B2 turned out to be more effective, as a result of which the concentration of TPH was reduced by 41.67% and PAH by 34.73%. Another issue was the phytoremediation of the pre-treated G6-3B2 soil with the use of Zea mays. The tests were carried out in three systems (system 1-soil G6-3B2 + Zea mays; system 2-soil G6-3B2 + biopreparation B2 + Zea mays; system 3-soil G6-3B2 + biopreparation B2 with γ-PGA + Zea mays) for 6 months. The highest degree of TPH and PAH reduction was obtained in system 3, amounting to 65.35% and 60.80%, respectively. The lowest phytoremediation efficiency was recorded in the non-inoculated system 1, where the concentration of TPH was reduced by 22.80% and PAH by 18.48%. Toxicological tests carried out using PhytotoxkitTM, OstracodtoxkitTM and Microtox® Solid Phase tests confirmed the effectiveness of remediation procedures and showed a correlation between the concentration of petroleum hydrocarbons in the soil and its toxicity. The results obtained during the research indicate the great potential of bioremediation practices with the use of microbial biopreparations and Zea mays in the treatment of soils contaminated with petroleum hydrocarbons.

Arsenic (As) oxidation by core endosphere microbiome mediates As speciation in Pteris vittata roots

Pteris vittata is an arsenic(As)-hyperaccumulator that may be employed in phytoremediation of As-contaminated soils. P. vittata-associated microbiome are adapted to elevated As and may be important for host survival under stresses. Although P. vittata root endophytes could be critical for As biotransformation in planta, their compositions and metabolisms remain elusive. The current study aims to characterize the root endophytic community composition and As-metabolizing potentials in P. vittata. High As(III) oxidase gene abundances and rapid As(III) oxidation activity indicated that As(III) oxidation was the dominant microbial As-biotransformation processes compared to As reduction and methylization in P. vittata roots. Members of Rhizobiales were the core microbiome and the dominant As(III) oxidizers in P. vittata roots. Acquasition of As-metabolising genes, including both As(III) oxidase and As(V) detoxification reductase genes, through horizontal gene transfer was identified in a Saccharimonadaceae genomic assembly, which was another abundant population residing in P. vittata roots. Acquisition of these genes might improve the fitness of Saccharimonadaceae population to elevated As concentrations in P. vittata. Diverse plant growth promoting traits were encoded by the core root microbiome populations Rhizobiales. We propose that microbial As(III) oxidation and plant growth promotion are critical traits for P. vittata survival in hostile As-contaiminated sites.

Trends in Harnessing Plant Endophytic Microbiome for Heavy Metal Mitigation in Plants: A Perspective

Plant microbiomes represent dynamic entities, influenced by the environmental stimuli and stresses in the surrounding conditions. Studies have suggested the benefits of commensal microbes in improving the overall fitness of plants, besides beneficial effects on plant adaptability and survival in challenging environmental conditions. The concept of 'Defense biome' has been proposed to include the plant-associated microbes that increase in response to plant stress and which need to be further explored for their role in plant fitness. Plant-associated endophytes are the emerging candidates, playing a pivotal role in plant growth, adaptability to challenging environmental conditions, and productivity, as well as showing tolerance to biotic and abiotic stresses. In this article, efforts have been made to discuss and understand the implications of stress-induced changes in plant endophytic microbiome, providing key insights into the effects of heavy metals on plant endophytic dynamics and how these beneficial microbes provide a prospective solution in the tolerance and mitigation of heavy metal in contaminated sites.

Biotechnology Advances in Bioremediation of Arsenic: A Review

Arsenic is a highly toxic metalloid widespread in the Earth's crust, and its contamination due to different anthropogenic activities (application of agrochemicals, mining, waste management) represents an emerging environmental issue. Therefore, different sustainable and effective remediation methods and approaches are needed to prevent and protect humans and other organisms from detrimental arsenic exposure. Among numerous arsenic remediation methods, those supported by using microbes as sorbents (microbial remediation), and/or plants as green factories (phytoremediation) are considered as cost-effective and environmentally-friendly bioremediation. In addition, recent advances in genetic modifications and biotechnology have been used to develop (i) more efficient transgenic microbes and plants that can (hyper)accumulate or detoxify arsenic, and (ii) novel organo-mineral materials for more efficient arsenic remediation. In this review, the most recent insights from arsenic bio-/phytoremediation are presented, and the most relevant physiological and molecular mechanisms involved in arsenic biological routes, which can be useful starting points in the creation of more arsenic-tolerant microbes and plants, as well as their symbiotic associations are discussed.

Use of Biostimulants as a New Approach for the Improvement of Phytoremediation Performance—A Review

Environmental pollution is one of the most pressing global issues, and it requires priority attention. Environmental remediation techniques have been developed over the years and can be applied to polluted sites, but they can have limited effectiveness and high energy consumption and costs. Bioremediation techniques, on the other hand, represent a promising alternative. Among them, phytoremediation is attracting particular attention, a green methodology that relies on the use of plant species to remediate contaminated sites or prevent the dispersion of xenobiotics into the environment. In this review, after a brief introduction focused on pollution and phytoremediation, the use of plant biostimulants (PBs) in the improvement of the remediation effectiveness is proposed. PBs are substances widely used in agriculture to raise crop production and resistance to various types of stress. Recent studies have also documented their ability to counteract the deleterious effects of pollutants on plants, thus increasing the phytoremediation efficiency of some species. The works published to date, reviewed and discussed in the present work, reveal promising prospects in the remediation of polluted environments, especially for heavy metals, when PBs derived from humic substances, protein and amino acid hydrolysate, inorganic salts, microbes, seaweed, plant extracts, and fungi are employed.

Phytoremediation of Heavy Metals: An Indispensable Contrivance in Green Remediation Technology

Environmental contamination is triggered by various anthropogenic activities, such as using pesticides, toxic chemicals, industrial effluents, and metals. Pollution not only affects both lotic and lentic environments but also terrestrial habitats, substantially endangering plants, animals, and human wellbeing. The traditional techniques used to eradicate the pollutants from soil and water are considered expensive, environmentally harmful and, typically, inefficacious. Thus, to abate the detrimental consequences of heavy metals, phytoremediation is one of the sustainable options for pollution remediation. The process involved is simple, effective, and economically efficient with large-scale extensive applicability. This green technology and its byproducts have several other essential utilities. Phytoremediation, in principle, utilizes solar energy and has an extraordinary perspective for abating and assembling heavy metals. The technique of phytoremediation has developed in contemporary times as an efficient method and its success depends on plant species selection. Here in this synthesis, we are presenting a scoping review of phytoremediation, its basic principles, techniques, and potential anticipated prospects. Furthermore, a detailed overview pertaining to biochemical aspects, progression of genetic engineering, and the exertion of macrophytes in phytoremediation has been provided. Such a promising technique is economically effective as well as eco-friendly, decontaminating and remediating the pollutants from the biosphere.

Unraveling the effects of arbuscular mycorrhizal fungi on cadmium uptake and detoxification mechanisms in perennial ryegrass (Lolium perenne)

Cadmium (Cd) is a major environmental pollutant and one of the most toxic metals in the environment. Arbuscular mycorrhizal fungi (AMF) assisted phytoremediation can be used to remove Cd from polluted soils but the role of AMF, which mediate in Cd accumulation and tolerance, remains poorly understood. Here we inoculated Lolium perenne with two different AMF species (Glomus etunicatum and Glomus mosseae). Mycorrhizal L. perenne and non-mycorrhizal controls were exposed to Cd stress and we tested the effects of AMF mycorrhization on Cd uptake and subsequent tolerance, as well as the underlying mechanisms. Mycorrhizal infection increased root Cd²⁺ uptake and we observed that net Cd²⁺ influx was coupled with net Ca²⁺ influx. The inactivation of Ca²⁺ transporter channels decreased Cd²⁺ uptake in non-inoculated roots to a greater extent than in inoculated roots, indicating that AMF activates additional ion transport channels. In consequence, inoculated plants exhibited higher Cd accumulation in both roots and shoots than non-inoculated controls. However, AMF-inoculated plants showed higher chlorophyll concentrations, photosynthesis, and growth under Cd, indicating lower Cd toxicity in AMF-inoculated plants, despite the increase in Cd uptake. We observed that AMF-inoculated favored the isolation of Cd within cell walls and vacuoles, and had higher concentrations of superoxide dismutase activity and glutathione concentration in roots than non-inoculated plants, consequently experiencing less stress upon Cd exposure. Our results highlight the potential and mechanism of AMF for enhancing phytoremediation of L. perenne in heavy metal contaminated environments.

Highly efficient detoxification of dinitrotoluene by transgenic switchgrass overexpressing bacterial nitroreductase

Dinitrotoluene (DNT) has been extensively used in manufacturing munitions, polyurethane foams and other important chemical products. However, it is highly toxic and mutagenic to most organisms. Here, we synthesized a codon-optimized bacterial nitroreductase gene, NfsI, for plant expression. The kinetic analysis indicates that the recombinant NfsI can detoxify both 2,4-DNT and its sulfonate (DNTS), while it has a 97.6-fold higher catalytic efficiency for 2,4-DNT than DNTS. Furthermore, we overexpressed NfsI in switchgrass (Panicum virgatum L.), which is a multiple-purpose crop used for fodder and biofuel production as well as phytoremediation. The 2,4-DNT treatment inhibited root elongation of wild-type switchgrass plants and promoted reactive oxygen species (ROS) accumulation in roots. In contrast, overexpression of NfsI in switchgrass significantly alleviated 2,4-DNT-induced root growth inhibition and ROS overproduction. Thus, the NfsI overexpressing transgenic switchgrass plant removed 94.1% 2,4-DNT after 6 days, whose efficiency was 1.7-fold higher than control plants. Moreover, the comparative transcriptome analysis suggests that 22.9% of differentially expressed genes induced by 2,4-DNT may participate in NfsI-mediated 2,4-DNT detoxification in switchgrass. Our work sheds light on the function of NfsI during DNT phytoremediation for the first time, revealing the application potential of switchgrass plants engineered with NfsI.

Enhanced phytoremediation of TNT and cobalt co-contaminated soil by AfSSB transformed plant

2,4,6-trinitrotoluene (TNT) and cobalt (Co) contaminants have posed a severe environmental problem in many countries. Phytoremediation is an environmentally friendly technology for the remediation of these contaminants. However, the toxicity of TNT and cobalt limit the efficacy of phytoremediation application. The present research showed that expressing the Acidithiobacillus ferrooxidans single-strand DNA-binding protein gene (AfSSB) can improve the tolerance of Arabidopsis and tall fescue to TNT and cobalt. Compared to control plants, the AfSSB transformed Arabidopsis and tall fescue exhibited enhanced phytoremediation of TNT and cobalt separately contaminated soil and co-contaminated soil. The comet analysis revealed that the AfSSB transformed Arabidopsis suffer reduced DNA damage than control plants under TNT or cobalt exposure. In addition, the proteomic analysis revealed that AfSSB improves TNT and cobalt tolerance by strengthening the reactive superoxide (ROS) scavenging system and the detoxification system. Results presented here serve as strong theoretical support for the phytoremediation potential of organic and metal pollutants mediated by single-strand DNA-binding protein genes. SUMMARIZES: This is the first report that AfSSB enhances phytoremediation of 2,4,6-trinitrotoluene and cobalt separately contaminated and co-contaminated soil.

Water Purification of Classical and Emerging Organic Pollutants: An Extensive Review

The main techniques used for organic pollutant removal from water are adsorption, reductive and oxidative processes, phytoremediation, bioremediation, separation by membranes and liquid–liquid extraction. In this review, strengths and weaknesses of the different purification techniques are discussed, with particular attention to the newest results published in the scientific literature. This study highlighted that adsorption is the most frequently used method for water purification, since it can balance high organic pollutants removal efficiency, it has the possibility to treat a large quantity of water in semi-continuous way and has acceptable costs.

Agronomic traits and ionomics influence on Cd accumulation in various sorghum (Sorghum bicolor (L.) Moench) genotypes

Cd is a common pollutant that contaminates the ecological environment of soil-crop systems and threatens food security and human health. Sorghum (Sorghum bicolor (L.) Moench) has a great potential for use as energy feedstock and Cd phytoremediation. Therefore, the identification of sorghum genotypes with high Cd accumulation is of great significance to Cd pollution remediation and production of bioenergy. A total of 126 biomass sorghum genotypes grown in a Cd-polluted field were investigated, and their agronomic traits were analyzed, including plant height, leaf number, shoot dry weight (SDW), soil and plant analyzer development (SPAD) value, and concentration of metal ions at seedling stage. Plant height was an important factor for screening potential biomass sorghum species because it presented a significant correlation with the Cd concentration in shoots and SDW (P < 0.01). The highest and lowest Cd concentration in sorghum shoots were 7.88 and 0.99 mg kg^-1, respectively. The Cd concentration presented a negative and significant correlation with Mn in sorghum shoots (r = -0.303, P < 0.01), which was in agreement with the results that sorghum species with high Cd concentrations have lower Mn concentrations. In the mature stage, sorghum 12530 presented higher Cd concentration and dry weight in shoots compared with other genotypes. In summary, plant height, SDW, and concentration of Mn in sorghum shoots are critical parameters that synthetically influence the accumulation of Cd in sorghum shoots.

Endophyte roles in nutrient acquisition, root system architecture development and oxidative stress tolerance

Plants associate with communities of microbes (bacteria and fungi) that play critical roles in plant development, nutrient acquisition and oxidative stress tolerance. The major share of plant microbiota is endophytes which inhabit plant tissues and help them in various capacities. In this article, we have reviewed what is presently known with regard to how endophytic microbes interact with plants to modulate root development, branching, root hair formation and their implications in overall plant development. Endophytic microbes link the interactions of plants, rhizospheric microbes and soil to promote nutrient solubilization and further vectoring these nutrients to the plant roots making the soil-plant-microbe continuum. Further, plant roots internalize microbes and oxidatively extract nutrients from microbes in the rhizophagy cycle. The oxidative interactions between endophytes and plants result in the acquisition of nutrients by plants and are also instrumental in oxidative stress tolerance of plants. It is evident that plants actively cultivate microbes internally, on surfaces and in soils to acquire nutrients, modulate development and improve health. Understanding this continuum could be of greater significance in connecting endophytes with the hidden half of the plant that can also be harnessed in applied terms to enhance nutrient acquisition through the development of favourable root system architecture for sustainable production under stress conditions.

An endophytic bacterial strain, Enterobacter cloacae TMX-6, enhances the degradation of thiamethoxam in rice plants

Thiamethoxam (TMX) has been widely used over the last two decades. TMX residue in the environment has drawn great public attention. An endophytic bacterial strain, TMX-6, capable of degrading TMX was isolated from wild Ophiopogon japonicus and was identified as Enterobacter cloacae by morphology and 16S ribosomal DNA sequence analysis. After being marked with green fluorescent protein plasmid, TMX-6 was successfully inoculated in the rice plants (Oryza sativa L.). The numbers of TMX-6 in non-TMX treated rice plants ranged from 3.9 to 4.6 log CFU g^-1 in the roots, and from 2.7 to 4.0 log CFU g^-1 in the shoots; while ranged from 3.9 to 5.3 log CFU g^-1 in roots and from 2.7 to 4.1 log CFU g^-1 in shoots of TMX treated rice plants. Nearly 28%, 33%, 77% and 99% of TMX was removed from the hydroponic medium (HM), HM with strain TMX-6, HM with uninoculated rice and HM with inoculated rice, respectively, at the end of a 21-day (d) experiment period, and the correspondent half-lives of TMX were 46.2, 38.5, 9.9 and 4.7 d, respectively. Eleven TMX metabolites were identified in both inoculated and uninoculated rice plants through metabolomics data analysis. The intensity of TMX- NH, TMX-urea and clothianidin increased more than 3 times in inoculated rice plants on day 6. This demonstrates the usefulness of the strain TMX-6 to enhance the degradation of TMX-contaminated substrates and reduce levels of toxic insecticides in crop plants.

Bioaugmenting the poplar rhizosphere to enhance treatment of 1,4-dioxane

1,4-Dioxane is a highly mobile and persistent groundwater pollutant that often forms large dilute plumes. Because of this, utilizing aggressive pump-and-treat and ex-situ technologies such as advanced oxidation can be prohibitively expensive. In this study, we bioaugmented the poplar rhizosphere with dioxane-degrading bacteria Mycobacterium dioxanotrophicus PH-06 or Pseudonocardia dioxanivorans CB1190 to enhance treatment of 1,4-dioxane in bench-scale experiments. All treatments tested removed 10 mg/L dioxane to near health advisory levels (<4 μg/L). However, PH-06-bioaugmented poplar significantly outperformed all other treatments, reaching <4 μg/L in only 13 days. Growth curve experiments confirmed that PH-06 could not utilize root extract as an auxiliary carbon source for growth. Despite this limitation, our findings suggest that PH-06 is a strong bioaugmentation candidate to enhance the treatment of dioxane by phytoremediation. In addition, we confirmed that CB1190 could utilize both 1,4-dioxane and root extract as substrates. Finally, we demonstrated the large-scale production of these two strains for use in the field. Overall, this study shows that combining phytoremediation and bioaugmentation is an attractive strategy to treat dioxane-contaminated groundwater to low risk-based concentrations (~1 μg/L).

Aquatic Macrophytes in Constructed Wetlands: A Fight against Water Pollution

There is growing concern among health institutions worldwide to supply clean water to their populations, especially to more vulnerable communities. Although sewage treatment systems can remove most contaminants, they are not efficient at removing certain substances that can be detected in significant quantities even after standard treatments. Considering the necessity of perfecting techniques that can remove waterborne contaminants, constructed wetland systems have emerged as an effective bioremediation solution for degrading and removing contaminants. In spite of their environmentally friendly appearance and efficiency in treating residual waters, one of the limiting factors to structure efficient artificial wetlands is the choice of plant species that can both tolerate and remove contaminants. For sometimes, the chosen plants composing a system were not shown to increase wetland performance and became a problem since the biomass produced must have appropriated destination. We provide here an overview of the use and role of aquatic macrophytes in constructed wetland systems. The ability of plants to remove metals, pharmaceutical products, pesticides, cyanotoxins and nanoparticles in constructed wetlands were compared with the removal efficiency of non-planted systems, aiming to evaluate the capacity of plants to increase the removal efficiency of the systems. Moreover, this review also focuses on the management and destination of the biomass produced through natural processes of water filtration. The use of macrophytes in constructed wetlands represents a promising technology, mainly due to their efficiency of removal and the cost advantages of their implantation. However, the choice of plant species composing constructed wetlands should not be only based on the plant removal capacity since the introduction of invasive species can become an ecological problem.

Unravelling the Role of Rhizospheric Plant-Microbe Synergy in Phytoremediation: A Genomic Perspective

Background

Accretion of organic and inorganic contaminants in soil interferes in the food chain, thereby posing a serious threat to the ecosystem and adversely affecting crop productivity and human life. Both endophytic and rhizospheric microbial communities are responsible for the biodegradation of toxic organic compounds and have the capability to enhance the uptake of heavy metals by plants via phytoremediation approaches. The diverse set of metabolic genes encoding for the production of biosurfactants and biofilms, specific enzymes for degrading plant polymers, modification of cell surface hydrophobicity and various detoxification pathways for the organic pollutants, plays a significant role in bacterial driven bioremediation. Various genetic engineering approaches have been demonstrated to modulate the activity of specific microbial species in order to enhance their detoxification potential. Certain rhizospheric bacterial communities are genetically modified to produce specific enzymes that play a role in degrading toxic pollutants. Few studies suggest that the overexpression of extracellular enzymes secreted by plant, fungi or rhizospheric microbes can improve the degradation of specific organic pollutants in the soil. Plants and microbes dwell synergistically, where microbes draw benefit by nutrient acquisition from root exudates whereas they assist in plant growth and survival by producing certain plant growth promoting metabolites, nitrogen fixation, phosphate solubilization, auxin production, siderophore production, and inhibition or suppression of plant pathogens. Thus, the plant-microbe interaction establishes the foundation of the soil nutrient cycle as well as decreases soil toxicity by the removal of harmful pollutants.

Conclusion

The perspective of integrating genetic approach with bioremediation is crucial to evaluate connexions among microbial communities, plant communities and ecosystem processes with a focus on improving phytoremediation of contaminated sites.

Novel Integration of Geopolymer Pavers, Silva Cells and Poplar Trees for In-Situ Treatment of Car-Wash Wastewater

This paper presents an eco-friendly, low-impact development (LID) approach, developed and implemented at a car wash site for a cleaner and greener environment. In this approach, the contaminated water discharged after car washing is treated as it is directed through an engineered, ecology-based water-management design. The design involves poplar (Populus deltoides) trees, Silva Cells®, and Fly-ash based Geopolymer concrete pavers working collectively to minimize the percolation of contaminants into the soil. In this novel system, each component has a vital role. For instance, the extensive roots of the poplar trees enable water filtration owing to phytoremediation effect; while the Silva Cells® promote stormwater management, planting of poplar trees and serve as a foundation for paver blocks. Lastly, the paver blocks made from industrial waste allow it to withstand urban load and infiltrate water runoff, thereby reducing runoff quantities. To evaluate the efficacy of contaminant uptake by this system, pH, electrical conductivity and turbidity, which are indicators of water quality levels, were monitored pre- and post-treatment. The percentage change in total dissolved solids indicates the potential of this treatment system for effective treatment of the contaminated car wash water.

Implementation of Floating Treatment Wetlands for Textile Wastewater Management: A Review

The textile industry is one of the most chemically intensive industries, and its wastewater is comprised of harmful dyes, pigments, dissolved/suspended solids, and heavy metals. The treatment of textile wastewater has become a necessary task before discharge into the environment. The textile effluent can be treated by conventional methods, however, the limitations of these techniques are high cost, incomplete removal, and production of concentrated sludge. This review illustrates recent knowledge about the application of floating treatment wetlands (FTWs) for remediation of textile wastewater. The FTWs system is a potential alternative technology for textile wastewater treatment. FTWs efficiently removed the dyes, pigments, organic matter, nutrients, heavy metals, and other pollutants from the textile effluent. Plants and bacteria are essential components of FTWs, which contribute to the pollutant removal process through their physical effects and metabolic process. Plants species with extensive roots structure and large biomass are recommended for vegetation on floating mats. The pollutant removal efficiency can be enhanced by the right selection of plants, managing plant coverage, improving aeration, and inoculation by specific bacterial strains. The proper installation and maintenance practices can further enhance the efficiency, sustainability, and aesthetic value of the FTWs. Further research is suggested to develop guidelines for the selection of right plants and bacterial strains for the efficient remediation of textile effluent by FTWs at large scales.

Ochrobactrum intermedium and saponin assisted phytoremediation of Cd and B[a]P co-contaminated soil by Cd-hyperaccumulator Sedum alfredii

Pot-culture experiments were conducted to investigate the potential of microorganism-saponin assisted phytoremediation of cadmium (Cd) and benzo(a)pyrene (B[a]P) co-contaminated soil using Cd-hyperaccumulator Sedum alfredii. Results showed that B[a]P-degrading bacterium (Ochrobactrum intermedium B[a]P-16) inoculation significantly increased root (by 22.1-24.1%) and shoot (by 20.5-23.4%) biomass of S. alfredii, whereas the application of saponin had no effect on the growth of S. alfredii. The saponin solution at 2 g L^-1 extracted more Cd and B[a]P than water, saponin enhanced Cd and B[a]P bioavailability in soil and thus promoted their uptake and accumulation in S. alfredii. The activity of B[a]P-16, dehydrogenase and polyphenol oxidase in co-contaminated soil was promoted by growing S. alfredii, and the application of B[a]P-16 and saponins caused a significant (P < 0.05) increase in both enzyme activities. The maximum B[a]P removal rate (82.0%) and Cd phytoextraction rate (19.5%) were obtained by co-application of S. alfredii with B[a]P-16 and saponin. The B[a]P-16 and plant promoted biodegradation were the predominant contributors towards removal of B[a]P from soil. A significant (P < 0.05) synergistic effect of B[a]P-16 and saponin on B[a]P and Cd removal efficiency was observed in this study. It is suggested that planting S. alfredii with application of B[a]P-16 and saponin would be an effective method for phytoremediation of soil co-contaminated with Cd and PAHs.

Combined Effects of Compost and Medicago Sativa in Recovery a PCB Contaminated Soil

The effectiveness of adding compost and the plant Medicago sativa in improving the quality of a soil historically contaminated by polychlorinated biphenyls (PCBs) was tested in greenhouse microcosms. Plant pots, containing soil samples from an area contaminated by PCBs, were treated with the compost and the plant, separately or together. Moreover, un-treated and un-planted microcosms were used as controls. At fixed times (1, 133 and 224 days), PCBs were analysed and the structure (cell abundance, phylogenetic characterization) and functioning (cell viability, dehydrogenase activity) of the natural microbial community were also measured. The results showed the effectiveness of the compost and plant in increasing the microbial activity, cell viability, and bacteria/fungi ratio, and in decreasing the amount of higher-chlorinated PCBs. Moreover, a higher number of α-Proteobacteria, one of the main bacterial groups involved in the degradation of PCBs, was found in the compost and plant co-presence.

Application of Floating Aquatic Plants in Phytoremediation of Heavy Metals Polluted Water: A Review

Heavy-metal (HM) pollution is considered a leading source of environmental contamination. Heavy-metal pollution in ground water poses a serious threat to human health and the aquatic ecosystem. Conventional treatment technologies to remove the pollutants from wastewater are usually costly, time-consuming, environmentally destructive, and mostly inefficient. Phytoremediation is a cost-effective green emerging technology with long-lasting applicability. The selection of plant species is the most significant aspect for successful phytoremediation. Aquatic plants hold steep efficiency for the removal of organic and inorganic pollutants. Water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes) and Duck weed (Lemna minor) along with some other aquatic plants are prominent metal accumulator plants for the remediation of heavy-metal polluted water. The phytoremediation potential of the aquatic plant can be further enhanced by the application of innovative approaches in phytoremediation. A summarizing review regarding the use of aquatic plants in phytoremediation is gathered in order to present the broad applicability of phytoremediation.

Molecular mechanisms in phytoremediation of environmental contaminants and prospects of engineered transgenic plants/microbes

Concerns about emerging environmental contaminants have been growing along with industrialization and urbanization around the globe. Among various options for remediating these contaminants, phytotechnology is suggested as a feasible option to maintain the environmental sustainability. The recent advances in phytoremediation, genetic/molecular/omics/metabolic engineering, and nanotechnology are opening new paths for efficient treatment of emerging organic/inorganic contaminants. In this respect, elucidation of molecular mechanisms and genetic engineering of hyperaccumulator plants is expected to enhance remediation of environmental contaminants. This review was organized to offer valuable insights into the molecular mechanisms of phytoremediation and the prospects of transgenic hyperaccumulators with enhanced stress tolerance to diverse contaminants such as heavy metals and metalloids, xenobiotics, explosives, poly aromatic hydrocarbons (PAHs), petroleum hydrocarbons, pesticides, and nanoparticles. The roles of genoremediation and nanoparticles in augmenting the phytoremediation technology are also described in an interrelated framework with biotechnological prospects (e.g., plant molecular nano-farming). Finally, political debate on the preferential use of crops versus non-crop hyperaccumulators in genoremediation, limitations of transgenics in phytotechnologies, and their public acceptance issues are discussed in the policy framework.

Phytoremediation and detoxification of xenobiotics in plants: herbicide-safeners as a tool to improve plant efficiency in the remediation of polluted environments. A mini-review

Phytoremediation is a widely studied and applied technology, based on the use of plants and their associated microorganisms to decontaminate polluted sites. In recent years, different strategies have been investigated to improve the phytoremediation efficiency of the selected plants. In this context, some studies have shown that herbicide-safeners, chemicals applied to crops to enhance their tolerance to herbicides, can increase the phytoremediation of soils and water polluted by organic and inorganic contaminants. Safeners, by inducing the xenobiotic detoxification and the antioxidant metabolism in plants, can enhance their removal potential in the cleaning process. In this review, after a short survey of phytoremediation technologies and the biochemical mechanisms activated by plants to tolerate and detoxify heavy metals and herbicides, the use of herbicide-safeners as a tool to increase the phytoremediation performance is reviewed and discussed.

Endophyte: Understanding the Microbes and its Applications

The ability of endophytes to colonize every plant tissue has led to the opportunity of using the microorganism in a lot of biological applications. Endophytes are beneficial to their host cells as such its application is observed in every aspects of life. This study therefore endeavored to give an analysis of endophytes, what they were and what they had been used for till the present time. Sampling of several literature studies in endophytes was done in this study to enable a complete understanding of the mechanism of application of the actions of endophytes, so as to be able to do a thorough assessment of the current state in the knowledge of the microbes. From the complete analysis of the literature on the application and use of endophytes, in nutrient asquition and increase the stress tolerance in plants. This study provided a platform for further research gaps through the presentation of what endophytes were, what they had been used for till date, the mechanism of operation of the micro-organism and the type of interaction between them and their hosts. There are still ways to improve on the methods of application of endophytes as a type of biological organism. This will be done by adjusting to the current trends in biological studies using molecular mechanization, following an intensive further study on endophyte mechanisms.

Endophytic Bacteria in in planta Organopollutant Detoxification in Crops

Microbe-assisted organopollutant removal, or in planta crop decontamination, is based on an interactive system between organopollutant-degrading endophytic bacteria (DEB_OP) and crops in alleviating organic toxins in plants. This script focuses on the fast-growing body of literature that has recently bloomed in organopollutant control in agricultural plants. The various facets of DEB_OP under study include their colonization, distribution, plant growth-promoting mechanisms, and modes of action in the detoxification process in plants. Also, an assessment of the biotechnological advances, advantages, and bottlenecks in accelerating the implementation of this decontamination strategy will be undertaken. The highlighted key research directions from this review will shape the future of agro-environmental sustainability and preservation of human health.

Hazardous heavy metals contamination of vegetables and food chain: Role of sustainable remediation approaches - A review

This review emphasizes the role of toxic metal remediation approaches due to their broad sustainability and applicability. The rapid developmental processes can incorporate a large quantity of hazardous and unseen heavy metals in all the segments of the environment, including soil, water, air and plants. The released hazardous heavy metals (HHMs) entered into the food chain and biomagnified into living beings via food and vegetable consumption and originate potentially health-threatening effects. The physical and chemical remediation approaches are restricted and localized and, mainly applied to wastewater and soils and not the plant. The nanotechnological, biotechnological and genetical approaches required to more rectification and sustainability. A cellular, molecular and nano-level understanding of the pathways and reactions are responsible for potentially toxic metals (TMs) accumulation. These approaches can enable the development of crop varieties with highly reduced concentrations of TMs in their consumable foods and vegetables. As a critical analysis by authors observed that nanoparticles could provide very high adaptability for both in-situ and ex-situ remediation of hazardous heavy metals (HHMs) in the environment. These methods could be used for the improvement of the inbuilt genetic potential and phytoremediation ability of plants by developing transgenic. These biological processes involve the transfer of gene of interest, which plays a role in hazardous metal uptake, transport, stabilization, inactivation and accumulation to increased host tolerance. This review identified that use of nanoremediation and combined biotechnological and, transgenic could help to enhance phytoremediation efficiency in a sustainable way.

Colonization of polycyclic aromatic hydrocarbon-degrading bacteria on roots reduces the risk of PAH contamination in vegetables

This is a primary investigation on the mitigation of polycyclic aromatic hydrocarbon (phenanthrene as a model PAH) contamination in vegetables including water spinach (Ipomoea aquatica Forsk), pakchoi (Brassica campestris) and Chinese cabbage (Brassica chinensis) using a gfp-labeled PAH-degrading bacterium (RS1-gfp). Effective root colonization led to dense RS1-gfp populations inhabiting the rhizosphere and endosphere of the vegetables, which subsequently led to a reduction in phenanthrene accumulation and risk in vegetables. When compared with the controls without RS1-gfp, the amount of phenanthrene accumulation due to strain RS1-gfp colonization reduced by up to ~93.7% in roots and ~75.2% in shoots of vegetables, respectively. The estimated incremental lifetime cancer risk (ILCR) for adults due to phenanthrene in vegetables was reduced by 24.6%-48% through RS1-gfp inoculation. The proposed method was developed to circumvent the risk of phenanthrene contamination in vegetables by inoculating PAH-degrading bacteria. The findings provide an in-depth understanding of PAH detoxification in agricultural plants grown on contaminated sites by exploiting bacteria like RS1-gfp, which portray both rhizo- and endophytic lifestyles.

Microcosm Experiment to Assess the Capacity of a Poplar Clone to Grow in a PCB-Contaminated Soil

Polychlorinated byphenyls (PCBs) are a class of Persistent Organic Pollutants extremely hard to remove from soil. The use of plants to promote the degradation of PCBs, thanks to synergic interactions between roots and the natural soil microorganisms in the rhizosphere, has been proved to constitute an effective and environmentally friendly remediation technique. Preliminary microcosm experiments were conducted in a greenhouse for 12 months to evaluate the capacity of the Monviso hybrid poplar clone, a model plant for phytoremediation, to grow in a low quality and PCB-contaminated soil in order to assess if this clone could be subsequently used in a field experiment. For this purpose, three different soil conditions (Microbiologically Active, Pre-sterilized and Hypoxic soils) were set up in order to assess the capacity of this clone to grow in the polluted soil in these different conditions and support the soil microbial community activity. The growth and physiology (chlorophyll content, chlorophyll fluorescence, ascorbate, phenolic compounds and flavonoid contents) of the poplar were determined. Moreover, chemical analyses were performed to assess the concentrations of PCB indicators in soil and plant roots. Finally, the microbial community was evaluated in terms of total abundance and activity under the different experimental conditions. Results showed that the poplar clone was able to grow efficiently in the contaminated soil and to promote microbial transformations of PCBs. Plants grown in the hypoxic condition promoted the formation of a higher number of higher-chlorinated PCBs and accumulated lower PCBs in their roots. However, plants in this condition showed a higher stress level than the other microcosms, producing higher amounts of phenolic, flavonoid and ascorbate contents, as a defence mechanism.

Review: Endophytic microbes and their potential applications in crop management

Endophytes are microbes (mostly bacteria and fungi) present asymptomatically in plants. Endophytic microbes are often functional in that they may carry nutrients from the soil into plants, modulate plant development, increase stress tolerance of plants, suppress virulence in pathogens, increase disease resistance in plants, and suppress development of competitor plant species. Endophytic microbes have been shown to: (i) obtain nutrients in soils and transfer nutrients to plants in the rhizophagy cycle and other nutrient-transfer symbioses; (ii) increase plant growth and development; (iii) reduce oxidative stress of hosts; (iv) protect plants from disease; (v) deter feeding by herbivores; and (vi) suppress growth of competitor plant species. Because of the effective functions of endophytic microbes, we suggest that endophytic microbes may significantly reduce use of agrochemicals (fertilizers, fungicides, insecticides, and herbicides) in the cultivation of crop plants. The loss of endophytic microbes from crop plants during domestication and long-term cultivation could be remedied by transfer of endophytes from wild relatives of crops to crop species. Increasing atmospheric carbon dioxide levels could reduce the efficiency of the rhizophagy cycle due to repression of reactive oxygen used to extract nutrients from microbes in roots. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparison of heavy metal accumulation ability in rainwater by 10 sponge city plant species

Rainwater heavy metal contamination is a growing problem worldwide, which damages the environment and human health. A primary challenge of sponge city designers is selecting suitable plants capable of surviving the toxic metals present in city rainwater. The concept of a sponge city to tackle urban surface-rainwater flooding and related urban rainwater management issues was established by People's Republic of China in 2014. Therefore, we studied the ability of sponge city plants to accumulate heavy metals from rainwater. Ophiopogon japonicus (Linn. f.) Ker-Gawl., Carex heterostachya Bge., Cornus officinalis Sieb. et Zucc., Sedum spectabile Boreau., Typha orientalis Presl., Lythrum salicaria L., Fatsia japonica (Thunb.) Decne. et Planch., Ilex chinensis Sims., Rosa chinensis Jacq., and Buxus bodinieri Levl. were selected as test plants, and their ability to accumulate four heavy metals (lead [Pb], cadmium [Cd], copper [Cu], and zinc [Zn]) was compared. Growth response and heavy metal accumulation across different species were compared over a 28-day enrichment cycle. The results showed that (1) Plant growth responses to heavy metals were significantly different. The most tolerant to heavy metals was Lythrum salicaria and the least tolerant was Rosa chinensis. (2) Concentrations of the heavy metals differed among sponge city plant species. In general, the concentration of Zn was highest, followed by Cu, Cd, and Pb. (3) The accumulation content of the same metal in different test species was related to the bioconcentration factor of the metal and the plant biomass. At the end of the enrichment cycle, Ophiopogon japonicus had the largest accumulation content for Pb, Cu, and Zn, and Lythrum salicaria had the highest accumulation content for Cd. (4) Considering the growth responses of plants and their final accumulation of heavy metals after the enrichment cycle, we concluded that Lythrum salicaria, Typha orientalis, and Ophiopogon japonicus are suitable for use in sponge cities to restore heavy metal-contaminated rainwater.

Vegetation type impacts microbial interaction with antimony contaminants in a mining-contaminated soil environment

Antimony (Sb) contamination is a growing environmental concern due to the increasing use of this metalloid in mining and industrial activities. The remediation of Sb-contaminated soil is a lengthy and costly process. Phytoremediation has been suggested as a cost-effective method for the long-term management of Sb-contaminated sites. Various plant types have been found to thrive in contaminated sites and have the potential to remediate Sb contamination; however, their impacts on Sb speciation and the indigenous microbial community remain unclear. In the current study, soils from three types of vegetation environment (i.e., grass, forest, and agricultural) were collected from two Sb mining areas in Guizhou, China. Comparisons of geochemical and microbiological properties among the three vegetation types revealed that vegetation was a major driver of soil biogeochemical characteristics. Contaminant fractions (i.e., extractable fractions of Sb and As) had a greater influence on microbial communities in grass and forest soil, whereas pH had a greater impact in agricultural soil. This difference may indicate distinct microbe-environment interactions in agricultural soil affected by anthropogenic activity. The dominant taxa, including Flavobacterium, Geobacter, Janthinobacterium, Clostridium, and Mycobacterium responded positively to various contaminant fractions, indicating that the community had adapted to the chronically contaminated environment. However, the regulation of these dominant genera by geochemical properties appears to be taxon-specific. Our results demonstrate that vegetation type has a substantial impact on Sb and As biogeochemical cycles, and should be considered in future remediation efforts.

On the Ecology of Selenium Accumulation in Plants

Plants accumulate and tolerate Se to varying degrees, up to 15,000 mg Se/kg dry weight for Se hyperaccumulators. Plant Se accumulation may exert positive or negative effects on other species in the community. The movement of plant Se into ecological partners may benefit them at low concentrations, but cause toxicity at high concentrations. Thus, Se accumulation can protect plants against Se-sensitive herbivores and pathogens (elemental defense) and reduce surrounding vegetation cover via high-Se litter deposition (elemental allelopathy). While hyperaccumulators negatively impact Se-sensitive ecological partners, they offer a niche for Se-tolerant partners, including beneficial microbial and pollinator symbionts as well as detrimental herbivores, pathogens, and competing plant species. These ecological effects of plant Se accumulation may facilitate the evolution of Se resistance in symbionts. Conversely, Se hyperaccumulation may evolve driven by increasing Se resistance in herbivores, pathogens, or plant neighbors; Se resistance also evolves in mutualist symbionts, minimizing the plant's ecological cost. Interesting topics to address in future research are whether the ecological impacts of plant Se accumulation may affect species composition across trophic levels (favoring Se resistant taxa), and to what extent Se hyperaccumulators form a portal for Se into the local food chain and are important for Se cycling in the local ecosystem.

Characterization and Initial Application of Endophytic Bacillus safensis Strain ZY16 for Improving Phytoremediation of Oil-Contaminated Saline Soils

Hydrocarbon-degrading and plant-growth-promoting bacterial endophytes have proven useful for facilitating the phytoremediation of petroleum-contaminated soils with high salinity. In this study, we identified Bacillus safensis strain ZY16 as an endophytic bacterium that can degrade hydrocarbons, produce biosurfactants, tolerate salt, and promote plant growth. The strain was isolated from the root of Chloris virgata Sw., a halotolerant plant collected from the Yellow River Delta. ZY16 survived in Luria-Bertani (LB) broth with 0–16% (w/v) sodium chloride (NaCl) and grew well in LB broth supplemented with 0–8% NaCl, indicating its high salt tolerance. The endophytic strain ZY16 effectively degraded C₁₂–C₃₂n-alkanes of diesel oil effectively, as well as common polycyclic aromatic hydrocarbons under hypersaline conditions. For example, in mineral salts (MS) liquid medium supplemented with 6% NaCl, ZY16 degraded n-undecane, n-hexadecane, n-octacosane, naphthalene, phenanthrene, and pyrene, with degradation percentages of 94.5, 98.2, 64.8, 72.1, 59.4, and 27.6%, respectively. In addition, ZY16 produced biosurfactant, as confirmed by the oil spreading technique, surface tension detection, and emulsification of para-xylene and paraffin. The biosurfactant production ability of ZY16 under hypersaline conditions was also determined. Moreover, ZY16 showed plant-growth-promoting attributes, such as siderophore and indole-3-acetic acid production, as well as phosphate solubilization. To assess the enhanced phytoremediation of saline soils polluted by hydrocarbons and the plant-growth-promotion ability of ZY16, a pot trial with and without inoculation of the endophyte was designed and performed. Inoculated and non-inoculated plantlets of C. virgata Sw. were grown in oil-polluted saline soil, with oil and salt contents of 10462 mg/kg and 0.51%, respectively. After 120 days of growth, significant enhancement of both the aerial and underground biomass of ZY16-inoculated plants was observed. The soil total petroleum hydrocarbon degradation percentage (a metric of phytoremediation) after incubation with ZY16 was 63.2%, representing an elevation of 25.7% over phytoremediation without ZY16 inoculation. Our study should promote the application of endophytic B. safensis ZY16 in phytoremediation by extending our understanding of the mutualistic interactions between endophytes and their host plants.

Enhancement of heavy metal tolerance and accumulation efficiency by expressing Arabidopsis ATP sulfurylase gene in alfalfa

Transgenic alfalfa (Medicago sativa L.) plants overexpressing the Arabidopsis ATP sulfurylase gene were generated using Agrobacterium-mediated genetic transformation to enhance their heavy metal accumulation efficiency. The ATP sulfurylase gene was cloned from Arabidopsis, following exposure to vanadium (V) and lead (Pb), and transferred into an Agrobacterium tumefaciens binary vector. This was co-cultivated with leaf explants of the alfalfa genotype Regen SY. Co-cultivated leaf explants were cultured on callus and somatic embryo induction medium, followed by regeneration medium for regenerating complete transgenic plants. The transgenic nature of the plants was confirmed using PCR and southern hybridization. The expression of Arabidopsis ATP sulfurylase gene in the transgenic plants was evaluated through RT-PCR. The selected transgenic lines showed increased tolerance to a mixture of five heavy metals and also demonstrated enhanced metal uptake ability under controlled conditions. The transgenic lines were fertile and did not exhibit any apparent morphological abnormality. The results of this study indicated an effective approach to improve the heavy metal accumulation ability of alfalfa plants which can then be used for the remediation of contaminated soil in arid regions.

Acetaminophen detoxification in cucumber plants via induction of glutathione S-transferases

Many pharmaceutical and personal care products (PPCPs) enter agroecosystems during reuse of treated wastewater and biosolids, presenting potential impacts on plant development. Here, acetaminophen, one of the most-used pharmaceuticals, was used to explore roles of glutathione (GSH) conjugation in its biotransformation in crop plants. Acetaminophen was taken up by plants, and conjugated quickly with GSH. After exposure to 5 mg L^-1 acetaminophen for 144 h, GSH-acetaminophen conjugates were 15.2 ± 1.3 nmol g^-1 and 1.2 ± 0.1 nmol g^-1 in cucumber roots and leaves, respectively. Glutathione-acetaminophen was also observed in common bean, alfalfa, tomato, and wheat. Inhibition of cytochrome P450 decreased GSH conjugation. Moreover, the GSH conjugate was found to further convert to cysteine and N-acetylcysteine conjugates. Glutathione S-transferase activity was significantly elevated after exposure to acetaminophen, while levels of GSH decreased by 55.4% in roots after 48 h, followed by a gradual recovery thereafter. Enzymes involved in GSH synthesis, regeneration and transport were consistently induced to maintain the GSH homeostasis. Therefore, GST-mediated conjugation likely played a crucial role in minimizing phytotoxicity of acetaminophen and other PPCPs in plants.

Integrating natural and engineered remediation strategies for water quality management within a low-impact development (LID) approach

The objective of this paper is to demonstrate an interdisciplinary strategy combining both engineering- and biology-based approaches for stormwater and wastewater treatment. The work involves a novel and environmentally friendly surface material that can withstand urban load over its design service life, allows preliminary treatment through filtration, and diverts water to the subsurface to conduct secondary treatment below the surface through phytoremediation via the extensive rooting systems of trees. The present study highlights an interdisciplinary low-impact development (LID) approach developed for a polluted industrial wastewater site, for a cleaner and greener environment. The LID system involves (i) rhizofiltration and phytoremediation methods for removing heavy metals and organic pollutants using a hybrid poplar and aspen species; (ii) porous infrastructure produced using industrial waste, referred to as geopolymer pavers; and (iii) use of Silva cells as a tree-friendly and load support system. The design of the pavers over the Silva cells is innovative as it can deal with rainwater runoff and urban transportation loads simultaneously. The proposed system has the ability to extract heavy metals that are common in urban runoff or domestic and industrial effluents thus preserving the ecosystem naturally. The test site is only 15 m², but designed for a water-retention capacity of 2 m³ (roughly 1:100 year design volume draining a 10 × 10 m parking lot), and remediation levels for Cu and Zn are expected to reach 180 mg/kg dry weight and 1200 mg/kg dry weight, respectively.

Low-thermal remediation of mercury-contaminated soil and cultivation of treated soil

In this study, low-thermal technology was used to treat the mercury contaminated farmland soil from a chemical plant in Guizhou Province, China. A series of field planting experiments were also aimed at determining the content of total and methyl-Hg in crop plants after thermal treatment. The results showed that the mercury concentration in soils was reduced about 70% from 255.74 mg/kg to 80.63 mg/kg when treated at 350 °C for 30 min in engineering-scale experiments, and the treated soil retained most of its original soil. Organic-bound and residual mercury in treated soil were reduced by 64.1 and 56.4% by means of a sequential extraction procedure, respectively. The total and methyl-mercury concentrations in crops decreased significantly, and the degree of soil mercury accumulation to crop roots has been reduced significantly. The total Hg concentrations in potato and corn were lower than the mercury tolerance limits for food in China, and the Hg concentration of radish was close to the limit. The technology provides a more sustainable remediation method for treating mercury-contaminated farmland soil in future engineering applications.

Expression of the human gene CYP1A2 enhances tolerance and detoxification of the phenylurea herbicide linuron in Arabidopsis thaliana plants and Escherichia coli

The phenylurea herbicide, linuron (LIN), is used to control various types of weeds. Despite its efficient role in controlling weeds, it presents a persistent problem to the environment. In the current study, phytoremediation properties of transgenic CYP1A2 Arabidopsis thaliana plants to LIN were assessed. CYP1A2 gene was firstly cloned and expressed in bacteria before proceeding to plants. In presence of LIN, The growth of CYP1A2 expressing bacteria was superior compared to control bacteria transformed with the empty bacterial expression vector pET22b(+). No clear morphological changes were detected on CYP1A2 transgenic plants. However, significant resistance to LIN herbicide application either via spraying the foliar parts of the plant or via supplementation of the herbicide in the growth medium was observed for CYP1A2 transformants. Plant growth assays under LIN stress provide strong evidence for the enhanced capacity of transgenic lines to grow and to tolerate high concentrations of LIN compared to control plants. HPLC analyses showed that detoxification of LIN by bacterial extracts and/or transgenic plant leaves is improved as compared to the corresponding controls. Our data indicate that over expression of the human CYP1A2 gene increases the phytoremediation capacity and tolerance of Arabidopsis thaliana plants to the phenylurea herbicide linuron.