Phytoremediation of triphenylmethane dyes by overexpressing a Citrobacter sp. triphenylmethane reductase in transgenic Arabidopsis

Sol-Gel Obtaining of TiO2/TeO2 Nanopowders with Biocidal and Environmental Applications

TiO2/TeO2 powders were obtained by an aqueous sol-gel method. Telluric acid (H6TeO6) and titanium butoxide were used as precursors. The as-prepared gel was step-wisely heated in the temperature range 200–700 °C and subsequently characterized by XRD, IR, and UV-Vis analysis and SEM. Mixtures containing TiO2 (anatase), α-TeO2 (paratellurite), and TiTe3O8 were established by XRD as final products, depending on heating temperature. The thermal stability of the obtained gels in the temperature range 100–400 °C was investigated. It was found by IR spectroscopy that the samples heated up to 300–400 °C consist mainly of an organic–inorganic amorphous phase which is transformed into an inorganic one above these temperatures. The microstructure of the gels was verified by scanning electron microscopy (SEM). The photocatalytic degradation of the synthesized nanopowders toward Malachite green organic dye (MG) was examined in order to evaluate the potential applications for environmental remediation. The prepared TiO2/TeO2 samples showed up to 60% decoloration efficiency after 120 min exposure to UV-light. The composition exhibited good antimicrobial activity against E. coli K12. The properties of the obtained material were investigated by the reactions of complete catalytic oxidation of different alkanes and toluene, and it could be suggested that TiO2/TeO2 powders are promising material for use as an active phase in environmental catalysts.

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.

Harnessing microbial gene pools to remediate persistent organic pollutants using genetically modified plants--a viable technology?

It has been 14 years since the international community came together to legislate the Stockholm Convention on Persistent Organic Pollutants (POPs), restricting the production and use of specific chemicals that were found to be environmentally stable, often bioaccumulating, with long-term toxic effects. Efforts are continuing to remove these pollutants from the environment. While incineration and chemical treatment can be successful, these methods require the removal of tonnes of soil, at high cost, and are damaging to soil structure and microbial communities. The engineering of plants for in situ POP remediation has had highly promising results, and could be a more environmentally-friendly alternative. This review discusses the characterization of POP-degrading bacterial pathways, and how the genes responsible have been harnessed using genetic modification (GM) to introduce these same abilities into plants. Recent advances in multi-gene cloning, genome editing technologies and expression in monocot species are accelerating progress with remediation-applicable species. Examples include plants developed to degrade 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), trichloroethylene (TCE), and polychlorinated biphenyls (PCBs). However, the costs and timescales needed to gain regulatory approval, along with continued public opposition, are considerable. The benefits and challenges in this rapidly developing and promising field are discussed.

Malachite green decolorization by the filamentous fungus Myrothecium roridum--Mechanistic study and process optimization

The filamentous fungus Myrothecium roridum isolated from a dye-contaminated area was investigated in terms of its use for the treatment of Malachite green (MG). The mechanisms involved in this process were established. Peroxidases and cytochrome P-450 do not mediate MG elimination. The laccase of M. roridum IM 6482 was found to be responsible for the decolorization of 8-11% of MG. Thermostable low-molecular-weight factors (LMWF) resistant to sodium azide were found to be largely involved in dye decomposition. In addition, MG decolorization by M. roridum IM 6482 occurred in a non-toxic manner. Data from antimicrobial tests showed that MG toxicity decreased after decolorization. To optimize the MG decolorization process, the effects of operational parameters (such as the medium pH and composition, process temperature and culture agitation) were examined. The results demonstrate that M. roridum IM 6482 may be used effectively as an alternative to traditional decolorization agents.

Phytoremediation of textile dyes and effluents: Current scenario and future prospects

Phytoremediation has emerged as a green, passive, solar energy driven and cost effective approach for environmental cleanup when compared to physico-chemical and even other biological methods. Textile dyes and effluents are condemned as one of the worst polluters of our precious water bodies and soils. They are well known mutagenic, carcinogenic, allergic and cytotoxic agents posing threats to all life forms. Plant based treatment of textile dyes is relatively new and hitherto has remained an unexplored area of research. Use of macrophytes like Phragmites australis and Rheum rhabarbarum have shown efficient removal of Acid Orange 7 and sulfonated anthraquinones, respectively. Common garden and ornamental plants namely Aster amellus, Portulaca grandiflora, Zinnia angustifolia, Petunia grandiflora, Glandularia pulchella, many ferns and aquatic plants have also been advocated for their dye degradation potential. Plant tissue cultures like suspension cells of Blumea malcolmii and Nopalea cochenillifera, hairy roots of Brassica juncea and Tagetes patula and whole plants of several other species have confirmed their role in dye degradation. Plants' oxidoreductases such as lignin peroxidase, laccase, tyrosinase, azo reductase, veratryl alcohol oxidase, riboflavin reductase and dichlorophenolindophenol reductase are known as key biodegrading enzymes which break the complex structures of dyes. Schematic metabolic pathways of degradation of different dyes and their environmental fates have also been proposed. Degradation products of dyes and their fates of metabolism have been reported to be validated by UV-vis spectrophotometry, high performance liquid chromatography, high performance thin layer chromatography, Fourier Transform Infrared Spectroscopy, gas chromatograph-mass spectroscopy and several other analytical tools. Constructed wetlands and various pilots scale reactors were developed independently using the plants of P. australis, Portulaca grandiflora, G. pulchella, Typha domingensis, Pogonatherum crinitum and Alternanthera philoxeroides. The developed phytoreactors gave noteworthy treatments, and significant reductions in biological oxygen demand, chemical oxygen demand, American Dye Manufacturers Institute color removal value, total organic carbon, total dissolved solids, total suspended solids, turbidity and conductivity of the dye effluents after phytoremediation. Metabolites of dyes and effluents have been assayed for phytotoxicity, cytotoxicity, genotoxicity and animal toxicity and were proved to be non/less toxic than untreated compounds. Effective strategies to handle fluctuating dye load and hydraulics for in situ treatment needs scientific attention. Future studies on development of transgenic plants for efficacious phytodegradation of textile dyes should be focused.