Engineering a catabolic pathway in plants for the degradation of 1,2-dichloroethane

Plants are increasingly being employed to clean up environmental pollutants such as heavy metals; however, a major limitation of phytoremediation is the inability of plants to mineralize most organic pollutants. A key component of organic pollutants is halogenated aliphatic compounds that include 1,2-dichloroethane (1,2-DCA). Although plants lack the enzymatic activity required to metabolize this compound, two bacterial enzymes, haloalkane dehalogenase (DhlA) and haloacid dehalogenase (DhlB) from the bacterium Xanthobacter autotrophicus GJ10, have the ability to dehalogenate a range of halogenated aliphatics, including 1,2-DCA. We have engineered the dhlA and dhlB genes into tobacco (Nicotiana tabacum ‘Xanthi’) plants and used 1,2-DCA as a model substrate to demonstrate the ability of the transgenic tobacco to remediate a range of halogenated, aliphatic hydrocarbons. DhlA converts 1,2-DCA to 2-chloroethanol, which is then metabolized to the phytotoxic 2-chloroacetaldehyde, then chloroacetic acid, by endogenous plant alcohol dehydrogenase and aldehyde dehydrogenase activities, respectively. Chloroacetic acid is dehalogenated by DhlB to produce the glyoxylate cycle intermediate glycolate. Plants expressing only DhlA produced phytotoxic levels of chlorinated intermediates and died, while plants expressing DhlA together with DhlB thrived at levels of 1,2-DCA that were toxic to DhlA-expressing plants. This represents a significant advance in the development of a low-cost phytoremediation approach toward the clean-up of halogenated organic pollutants from contaminated soil and groundwater

Monodehydroascorbate reductase mediates TNT toxicity in plants

The explosive 2,4,6-trinitrotoluene (TNT) is a highly toxic and persistent environmental pollutant. Due to the scale of affected areas, one of the most cost-effective and environmentally friendly means of removing explosives pollution could be the use of plants. However, mechanisms of TNT phytotoxicity have been elusive. Here, we reveal that phytotoxicity is caused by reduction of TNT in the mitochondria, forming a nitro radical that reacts with atmospheric oxygen, generating reactive superoxide. The reaction is catalyzed by monodehydroascorbate reductase 6 (MDHAR6), with Arabidopsis deficient in MDHAR6 displaying enhanced TNT tolerance. This discovery will contribute toward the remediation of contaminated sites. Moreover, in an environment of increasing herbicide resistance, with a shortage in new herbicide classes, our findings reveal MDHAR6 as a valuable plant-specific target

Industry-Informed Workshops to Develop Graduate Skill Sets in the Circular Economy Using Systems Thinking

Increasing demand for chemicals worldwide, depleting resources, consumer pressure, stricter legislation, and the rising cost of waste disposal are placing increasing pressure on chemical and related industries. For any organization to survive in the current arena of growing climate change laws and regulations, and increasing public influence, the issue of sustainability must be fundamental to the way it operates. A sustainable manufacturing approach will enable economic growth to be combined with environmental and social sustainability and will be realized via collaboration between a multidisciplinary community including chemists, biologists, engineers, environmental scientists, economists, experts in management, and policy makers. Hence, employees with new skills, knowledge, and experience are essential. To realize this approach, the design and development of a series of workshops encompassing systems thinking are presented here. After close consultation with industry, an annual program of interactive workshops has been designed for graduate students to go beyond examining the "greening" of chemical reactions, processes, and products, and instead embed a systems thinking approach to learning. The workshops provide a valuable insight into the issues surrounding sustainable manufacturing covering change management, commercialization, environmental impact, circular economy, legislation, and bioresources incorporating the conversion of waste into valuable products. The multidisciplinary course content incorporates industrial case studies, providing access to real business issues, and is delivered by experts from academic departments across campus and industry

Investigating the toxicity, uptake, nanoparticle formation and genetic response of plants to gold.

We have studied the physiological and genetic responses of Arabidopsis thaliana L. (Arabidopsis) to gold. The root lengths of Arabidopsis seedlings grown on nutrient agar plates containing 100 mg/L gold were reduced by 75%. Oxidized gold was subsequently found in roots and shoots of these plants, but gold nanoparticles (reduced gold) were only observed in the root tissues. We used a microarray-based study to monitor the expression of candidate genes involved in metal uptake and transport in Arabidopsis upon gold exposure. There was up-regulation of genes involved in plant stress response such as glutathione transferases, cytochromes P450, glucosyl transferases and peroxidases. In parallel, our data show the significant down-regulation of a discreet number of genes encoding proteins involved in the transport of copper, cadmium, iron and nickel ions, along with aquaporins, which bind to gold. We used Medicago sativa L. (alfalfa) to study nanoparticle uptake from hydroponic culture using ionic gold as a non-nanoparticle control and concluded that nanoparticles between 5 and 100 nm in diameter are not directly accumulated by plants. Gold nanoparticles were only observed in plants exposed to ionic gold in solution. Together, we believe our results imply that gold is taken up by the plant predominantly as an ionic form, and that plants respond to gold exposure by up-regulating genes for plant stress and down-regulating specific metal transporters to reduce gold uptake

Phytocat - a bio-derived Ni catalyst for rapid de-polymerization of polystyrene using a synergistic approach

Environmentally-friendly recycling of polystyrene and disposal of metal-containing plant biomass from phytoremediation sites are major challenges. Strategies beyond waste-to-energy that can harness the circular chemical potential of such feed-stocks are needed. We present a “triple-green” approach using microwave irradiation (250 °C, 200 W, <10 min) for the accelerated de-polymerization of polystyrene and valorization of nickel-contaminated biomass to yield valuable chemical building blocks. Biomass from soil-grownStackhousia tryoniiplants that naturally hyperaccumulate nickel (1.5 wt%), alongside non-hyperaccumulator, hydroponically-grown willow (Salix viminalis, 0.1 wt% Ni) was tested. The presence of naturally-bound nickel in carbonized biomass (Ni-phytocat) fromS. tryoniiandS. viminaliswas shown to significantly accelerate de-polymerization (74% and 69% styrene selectivity; 18 kJ g−1and 24 kJ g−1microwave energy consumed, respectively) when compared to controlS. viminalis(<0.01 wt% Ni; 56%; 42 kJ g−1) and activated carbon (57%; 36 kJ g−1). The Ni-phytocat offered significant advantage in enabling rapid de-polymerization of polystyrene with up to 91% conversion efficiency as compared to control phytocat (up to 82%) and activated carbon (up to 79%) within 5 min. Use of this synergistic effect of bio-derived Ni and microwaves to maximize the de-polymerization efficiency is proposed

Diphenylarsinic acid sorption mechanisms in soils using batch experiments and EXAFS spectroscopy

Diphenylarsinic acid (DPAA) is a phenyl arsenic compound derived from chemical warfare weapons. Macroscopic and microscopic work on DPAA sorption will provide useful information in predicting the partitioning and mobility of DPAA in the soil-water environment. Here, batch experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to investigate the sorption mechanisms of DPAA. The DPAA sorption data from 11 soil types was found to fit the Freundlich equation, and the sorption capacity, K-f, was significantly and positively correlated with oxalate-extractable Fe2O3. The K-f values of eight of the 11 untreated soils (1.51-113.04) significantly decreased upon removal of amorphous metal (hydr)oxides (0.51-13.37). When both amorphous and crystalline metal (hydr)oxides were removed from the untreated soils, the K-f values either decreased or slightly increased (0.65-3.09). Subsequent removal of soil organic matter from these amorphous and crystalline metal (hydr)oxide-depleted samples led to further decreases in K-f to 0.02-1.38, with only one exception (Sulfic Aquic-Orthic Halosols). These findings strongly suggest that ligand exchange reactions with amorphous metal (hydr)oxides contribute most to DPAA sorption on soils. EXAFS data provide further evidence that DPAA primarily formed bidentate binuclear (C-2) and monodentate mononuclear (V-1) coring-sharing complexes with As-Fe distances of 3.34 and 3.66 angstrom, respectively, on Fe (hydr)oxides. Comparison of these results with earlier studies suggests that C-2 and V-1 complexes of DPAA may be favored under low and high surface coverages, respectively, with the formation of V-1 bonds possibly conserving the sorption sites or decreasing the steric hindrance derived from phenyl substituents. (C) Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature 202